More

Identifying south facing mountain land, above an elevation, within a slope range, less than fixed distance from major roadways


This odd question comes from believing that such an analysis is plausible in a GIS system.

Only, I don't how to accomplish the various discrete steps implied from the Title, nor where to get a topo map that already has the iso-elevation contour lines developed in some GIS format, nor how to color in areas which face SW-to-SE, nor how to decipher the physical slope from the proximity of iso-elevation lines.

All these things, sensible to the engineer in me, but wondering what set of stackexchange questions (or other resources) might even begin to answer my question…

… in my ideal world, I scan in a USGS Topo map for the region of my interest, and out the other end of my QGIS black-box procedure comes a map with polygons lit up as my areas of interest.

What tools and techniques… ? Learning resources… ?

[and, if anyone wants to suggest 4 other appropriate tags, let me know… ]


The following is a rough outline of what you might do. I won't include a great deal of detail, you can research further using these terms and/or ask new more specific questions.

Note: you will need to careful of coordinate systems. Firstly that they are the same for your datasets, and second that they use metric (metres) horizontal units (not actually essential, but there are a number of "gotchas" that will creep in otherwise). You may need to reproject one or more datasets.

  1. Get a Digital Elevation Model (DEM) in raster format from the NED (alternatives are SRTM or Aster, both downloadable free from earthexplorer.usgs.gov).
  2. Get roadway data in vector format. I don't know the best source for this, I just googled and came up with the NHPN dataset for U.S. Roadways.
  3. Use QGIS to calculate Slope and Aspect from your DEM (QGIS Toolbar->Raster->Terrain Analysis->Slope/Aspect… )
  4. Convert your roadway data to raster with the same dimensions and pixel size as your DEM (QGIS Toolbar->Raster->Conversion->Rasterize).
    • Hint - the Rasterize tool can create a new raster or burn values into an existing one. The easiest way to ensure your roadway/highway/interstate raster has the same dimensions as your DEM is to rasterize into an existing raster with those dimensions. To create an empty raster based on your DEM dimensions, in the Raster Calculator (QGIS Toolbar->Raster->Raster Calculator) create an expression that will ensure all output values are zero, something like"[email protected]" = 99999
  5. Use QGIS to calculate distance to interstates raster (QGIS Toolbar->Raster->Analysis->Proximity)
  6. Use the QGIS Toolbar->Raster->Raster Calculator to create an expression that specifies your criteria, something like:("[email protected]" > 1000) AND (("[email protected]" >= 135) AND ( "[email protected]" <= 225)) AND (("[email protected]" >= 10) AND ("[email protected]" <= 35)) AND ("[email protected]" <= 10000)
  7. Convert to polygon (vector) format if desired - QGIS Toolbar->Raster->Conversion->Polygonize

Abstract

Hill areas have gained considerable attention in recent years because of continuously increasing demand for infrastructure facilities. Spatial planning of infrastructure facilities is a challenging task in hill areas because of topographical variations, ecological sensitivity, and extreme climatic conditions. This becomes more critical because of the lack of an integrated quantitative approach for the assessment of land for its suitability. The paper aims at the spatial suitability assessment for planning infrastructure facilities at site level in hill areas. This has been accomplished in four stages identification of the criteria, determination of weights of the criteria, spatial suitability assessment of the site, and scenario generation. In the first stage, a structured literature survey was done for the identification of the criteria influencing spatial planning of infrastructure facilities in the hill areas. In the second stage, an expert questionnaire survey was conducted for determining the percentage influence of the criteria and the responses were analysed through the analytical hierarchy process. In the third stage, spatial suitability map was generated in geographic information system for locating the infrastructure facilities. The vulnerability map was created for identifying the hazard prone areas. In the fourth stage, the developed suitability map and vulnerability map were aggregated to generate the scenario. A case study was taken for the implementation of the developed methodology which is useful for decision making for practitioners involved in the planning of infrastructure facilities in hill areas.


Physical features

The Canadian Rockies include the Mackenzie and Selwyn mountains of the Yukon and Northwest Territories (sometimes called the Arctic Rockies) and the ranges of western Alberta and eastern British Columbia. The Northern Rockies include the Lewis and Bitterroot ranges of western Montana and northeastern Idaho. These ranges formed along the eastern edge of a region of carbonate sedimentation some 17 miles (27 km) thick, which had accumulated from the late Precambrian to early Mesozoic time (i.e., between about 1 billion and 190 million years ago). This structural depression, known as the Rocky Mountain Geosyncline, eventually extended from Alaska to the Gulf of Mexico and became a continuous seaway during the Cretaceous Period (about 145 to 66 million years ago). The ranges of the Canadian and Northern Rockies were created when thick sheets of Paleozoic limestones were thrust eastward over Mesozoic rocks during the mountain-building episode called the Laramide Orogeny (65 to 35 million years ago). Some of these thrust sheets have moved 20 to 30 miles (32 to 48 km) to their present positions. The western margin of the Canadian Rockies and Northern Rockies is marked by the Rocky Mountain Trench, a graben (downfaulted, straight, flat-bottomed valley) up to 3,000 feet (900 metres) deep and several miles wide that has been glaciated and partially filled with deposits from glacial meltwaters.

The Columbia Icefield is situated on the continental divide in the Canadian Rockies at elevations of 10,000 to 13,000 feet (3,000 to 4,000 metres) above sea level. It includes the large Athabasca Glacier, which is nearly five miles long and about a mile wide. Glaciers in this ice field, while continuing to move, are thinning and retreating. The Canadian Rockies are about equally divided between drainage to the east (Atlantic and Arctic oceans) and west (Pacific Ocean).

The Middle Rockies include the Bighorn and Wind River ranges in Wyoming, the Wasatch Range of southeastern Idaho and northern Utah, and the Uinta Mountains of northeastern Utah the Absaroka Range, extending from northwestern Wyoming into Montana, serves as a link between the Northern and Middle Rockies. While the massive deposition of carbonates was occurring in the Canadian and Northern Rockies from the late Precambrian to the early Mesozoic, a considerably smaller quantity of clastic sediments was accumulating in the Middle Rockies. Mountain building there resulted from compressional folding and high-angle faulting, except for the low-angle thrust-faulting in southwestern Wyoming and southeastern Idaho. The granitic core of the anticlinal mountains often has been upfaulted, and many ranges are flanked by Paleozoic sedimentary rocks (e.g., shales, siltstones, and sandstones) that have been eroded into hogback ridges. This same mountain-building process is occurring today in the Andes Mountains of South America. Most mountain building in the Middle Rockies occurred during the Laramide Orogeny, but the mountains of the spectacular Teton Range attained their height less than 10 million years ago by moving more than 20,000 vertical feet relative to the floor of Jackson Hole along an east-dipping fault.

The Bighorn, Wind River, and Uinta ranges all form sharp ridge lines that rise above surrounding basins. The Wind River Range supports a large area of glaciers, including Dinwoody Glacier. These glaciers, however, are retreating fairly rapidly.

Geologic events in the Middle Rockies strongly influenced the direction of stream courses. A special feature of the past 10 million years was the creation of rivers that flowed from basin floors into canyons across adjacent mountains and onto the adjacent plains. This phenomenon resulted from superposition of the streams. The stream courses were initially established in the late Miocene Epoch (about 11.6 to 5.3 million years ago), when the basins were largely filled by deposits of Neogene and Paleogene age (i.e., about 2.6 to 66 million years old) that locally extended across lower segments of mountain axes. During the subsequent regional excavation of the basin fills—which began about five million years ago—the streams maintained their courses across the mountains and cut deep, transverse canyons.

The Yellowstone-Absaroka region of northwestern Wyoming is a distinctive subdivision of the Middle Rockies. A large magma chamber beneath the area has filled several times and caused the surface to bulge, only to then empty in a series of volcanic eruptions of basaltic and rhyolitic lava and ash. Three such cycles have occurred in the past two million years, the most recent of which occurred about 600,000 years ago. The magma chamber is currently filling again, and the land surface in Yellowstone is rising or tilting a slight amount each year.

The Southern Rockies include the Front Range and the Wet and Sangre de Cristo mountains along the eastern slope and the Park, Gore, and Sawatch ranges and the San Juan Mountains along the western slope. The eastern and western ranges are separated by a series of high basins: from north to south they are North Park, the Arkansas River valley, and the San Luis Valley. The Southern Rockies extend northward into southern Wyoming in three prongs: the Laramie and Medicine Bow mountains and the Sierra Madre.

Only about 5,000 feet of sediment accumulated during middle Mesozoic times (about 200 to 150 million years ago) in the region now occupied by the Southern Rockies. Mountain building in these ranges resulted from compressional folding and high-angle faulting during the Laramide Orogeny, as the Mesozoic sedimentary rocks were arched upward over a massive batholith of crystalline rock. Some 10,000 vertical feet of the sedimentary rocks were then eroded otherwise the Front Range would be approximately twice its present height. The Southern Rockies experienced less of the low-angle thrust-faulting that characterizes the Canadian and Northern Rockies and the western portions of the Middle Rockies.

The ranges of the Southern Rockies are higher than those of the Middle or Northern Rockies, with many peaks exceeding elevations of 14,000 feet. Colorado has 53 peaks over this elevation, the highest being Mount Elbert in the Sawatch Range, which at 14,433 feet (4,399 metres) is the highest point in the Rockies. These ranges were heavily eroded by several episodes of glaciation—the most recent ended about 7,500 years ago, and no active glaciers remain—resulting in spectacular alpine scenery. River valleys have been deepened in the past two million years, first from the direct action of glacier ice and subsequently by glacial meltwaters. Looping, knife-edged moraines occur in most valleys, marking the downslope extent of past glaciations.

The physiographic province called the Colorado Plateau in southeastern Utah, southwestern Colorado, northern Arizona, and northwestern New Mexico is another high-elevation region of the western United States, although it lacks the history of folding, faulting, and volcanic activity of adjacent regions. The uplifts in the Colorado Plateau are not as great as those elsewhere in the Rockies, and therefore less erosion has occurred Precambrian rocks have been exposed only in the deepest canyons, such as the Grand Canyon.

The plateau is actually a series of plateaus at different elevations arranged in a stairstep sequence through faulting. The horizontal sedimentary rocks have been dissected by the Green and Colorado rivers and their tributaries into a network of deep canyons. Some of these canyons are deeply entrenched meanders, such as the dramatic Goosenecks section of the San Juan River near Mexican Hat, Utah, where erosion through the canyon walls separating opposite sides of a meandering river loop has created a natural bridge.

The Grand Canyon of the Colorado River cuts across the southern end of the Kaibab Upwarp in the southern plateau region. The canyon is up to 6,600 feet (2,000 metres) deep and exposes a remarkable sequence of sedimentary rocks. Weak rock types, such as shale and softer sandstone layers, form low-sloping benches, while more resistant rock types, such as limestone and harder sandstone layers, comprise cliff-forming units. Because of the alternating sequence of weak and resistant rocks in the canyon walls, a cliff-and-bench topography has formed that is typical of much of the Colorado Plateau region. The headward erosion of streams into the plateau surface eventually isolates sections of the plateau into mesas, buttes, monuments, and spires. Bedrock that has been fractured into series of parallel joints can weather into high rock walls known as fins. Subsequent weathering leads to the creation of natural arches. The same weathering processes on cliffs can create niches, which have been exploited by cliff-dwelling Native American cultures in the past.

Four mountain groups—the La Sal, Henry, Abajo, and Carrizo—are notable. From a central pipelike intrusion reaching deep into Earth’s crust, magma has been injected between layers of sedimentary rock, causing the overlying beds to bulge up in domes about one mile across. These domes are called laccoliths, and each of these mountain massifs is made up of a group of laccoliths.


Physiography

The arrangement of the ranges in the system can be visualized as being in the shape of an extremely elongated H with a closed base. From north to south the west side of the H is made up of the ranges of the Queen Charlotte Islands and Vancouver Island, the Olympic Mountains, and the Washington, Oregon, and California Coast Ranges. From north to south the east side of the H consists of the Canadian Coast Mountains, the Cascade Range, and the Sierra Nevada. The Klamath Mountains of southern Oregon and northern California make up the east-west cross in the centre of the H, while the Transverse Ranges bend eastward from the California Coast Ranges to form the closed base of the H. Inside the H north of the Klamath Mountains are the drowned inside passage of British Columbia, the Puget Sound Lowland of Washington, and the Willamette River valley of Oregon. Inside the H south of the Klamath Mountains is the Central Valley of California.

Coastal plains are either narrow or nonexistent along the entire north-south extent of the coastal ranges. Offshore a narrow continental shelf drops abruptly into ocean depths. In places, waves have cut notches and terraces as the land has risen episodically. More-resistant igneous rocks stand as sea cliffs with undercut notches. Softer sedimentary rocks have been eroded to form embayments. There is evidence for the periodic rise and fall of the coast as a result of tectonic activity.

The ranges of Vancouver Island and the Queen Charlotte Islands have been heavily glaciated. Stream valleys have been deepened by glaciers to produce a fjordlike coast, with relatively short streams draining the interior. Southward, across the Juan de Fuca Strait, the Olympic Mountains rise to almost 8,000 feet (2,440 metres). The highest and most spectacular of the Coast Ranges, they consist of folded sedimentary and metamorphic rock and also have been heavily glaciated. Drainage is radial from the highest peaks among the major streams are the Hoh, Quinault, and Elwha.

The Canadian Coast Mountains and North Cascades differ structurally from the Middle and South Cascades. These northern ranges consist of a dissected upland of late Paleozoic rock (i.e., about 300 million years old) that has been folded, metamorphosed, and intruded by granites. Ridges in the North Cascades rise to elevations between 6,000 and 8,000 feet (1,830 to 2,440 metres) above these ridges stand the composite volcanic cones of Glacier Peak and Mount Baker. The Coast Mountains of British Columbia are considerably lower, with the highest elevations reaching 3,000 to 4,000 feet (910 to 1,220 metres) in the south. The higher peaks, however, often are glacier-covered. All the ranges have been heavily dissected by running water both before and after the Pleistocene Epoch (about 2,600,000 to 11,700 years ago). During the Pleistocene they were covered by a cordilleran ice sheet, the glaciers of which occupied and deepened many existing stream valleys. On the east side of the North Cascades, Lake Chelan is in a glacially formed valley, and its deepest points are more than 1,500 feet (460 metres) below the surface. In the Coast Mountains glacial action has produced a spectacular fjorded coast. Farther south in southern British Columbia and Washington are deep glacial valleys opening out onto the Fraser River delta and the Puget Sound Lowland.

The Middle Cascades, which extend southward from west-central Washington into Oregon, are an uplifted and faulted region consisting of volcanics from the Cenozoic Era (i.e., the past 65 million years). These volcanics consist of successive layers of tuffs, breccias, and mudflows, covered by basaltic flows. The range can be divided into eastern and western sections, the western being the oldest. Capping the higher, eastern part of the range is a more recent layer of Cenozoic andesites and basalts. Elevations reach 4,000 to 6,000 feet (1,220 to 1,830 metres), with a number of volcanic peaks—such as Mounts Rainier and Hood—standing high above the general surface relief. Rainier, at 14,410 feet (4,392 metres), is the highest peak in the Pacific mountain system, unless the Sierra Nevada is included in it, which makes its Mount Whitney (14,494 feet [4,418 metres]) the system’s tallest mountain.

The Columbia River cuts through the Middle Cascades in a magnificent gorge. On the southern (Oregon) side are numerous hanging valleys with streams that plunge in spectacular waterfalls into the gorge. The 620-foot (190-metre) single drop at Multnomah Falls is second in height in the United States only to Yosemite Falls in California. About 12,000 to 10,000 years ago, a large lake ( Lake Missoula) was impounded by an ice dam in western Montana. On several occasions the dam gave way and released enormous quantities of water, which then rapidly drained to the sea. Those floods deepened and widened the existing Columbia River valley and were largely responsible for the present profile of the gorge.

The South Cascades, extending from southern Oregon into northern California, differ from the Middle Cascades in that they were not uplifted. Even so, two of the major volcanoes in the western United States, Lassen Peak and Mount Shasta, surmount the range. The Pit River provides a low-elevation passage across these mountains.

The Klamath Mountains are the oldest of the Pacific coastal mountains, dating to the early Paleozoic Era (i.e., about 500 million years ago). They are extremely complex, probably resulting from the collision of tectonic plates in the early Triassic Period (about 250 million to 245 million years ago). Later they were intruded by granite batholiths. The Klamath Mountains have been glaciated in their higher elevations and have been heavily dissected by streams the major watercourse crossing them is the Rogue River.

Both the Coast and the Transverse ranges were formed by plate collisions. The Washington and Oregon Coast Ranges consist of folded gray mudstones and siltstones oriented in a north-south direction. The major streams are antecedent to the uplift and have been drowned in their lower courses, producing estuaries. In addition to the Columbia, these include the Umpqua and Siuslaw rivers. The California Coast Ranges also are made up of folded and faulted sedimentary rocks. The major faults trend northwest-southeast, however, and the rivers tend to follow these lines of weakness. The San Andreas Fault, passing through the southern California ranges, more or less bisects them before heading offshore near San Francisco. North of San Francisco Bay are the Napa, Russian, Eel, and Klamath rivers, while the Salinas River is the major coastal stream south of the bay. The eastern section of the Transverse Ranges consists of granites and metamorphic rocks, while the western portion resembles the sedimentary structure of the Coast Ranges streams draining them include the Santa Clara and Santa Ana rivers.


Identifying south facing mountain land, above an elevation, within a slope range, less than fixed distance from major roadways - Geographic Information Systems

Flight Environment

PREVAILING WINDS

    Hadley cell - Low latitude air movement toward the equator that with heating, rises vertically, with poleward movement in the upper atmosphere. This forms a convection cell that dominates tropical and sub-tropical climates.

There are two main forces which affect the movement of air in the upper levels. The pressure gradient causes the air to move horizontally, forcing the air directly from a region of high pressure to a region of low pressure. The Coriolis force, however, deflects the direction of the flow of the air (to the right in the Northern Hemisphere) and causes the air to flow parallel to the isobars.

Winds in the upper levels will blow clockwise around areas of high pressure and counterclockwise around areas of low pressure.

The speed of the wind is determined by the pressure gradient. The winds are strongest in regions where the isobars are close together.

Surface friction plays an important role in the speed and direction of surface winds. As a result of the slowing down of the air as it moves over the ground, wind speeds are less than would be expected from the pressure gradient on the weather map and the direction is changed so that the wind blows across the isobars into a center of low pressure and out of a center of high pressure.

The effect of friction usually does not extend more than a couple of thousand feet into the air. At 3000 feet above the ground, the wind blows parallel to the isobars with a speed proportional to the pressure gradient.

Even allowing for the effects of surface friction, the winds, locally, do not always show the speed and direction that would be expected from the isobars on the surface weather map. These variations are usually due to geographical features such as hills, mountains and large bodies of water. Except in mountainous regions, the effect of terrain features that cause local variations in wind extends usually no higher than about 2000 feet above the ground.

Land and sea breezes are caused by the differences in temperature over land and water. The sea breeze occurs during the day when the land area heats more rapidly than the water surface. This results in the pressure over the land being lower than that over the water. The pressure gradient is often strong enough for a wind to blow from the water to the land.

The land breeze blows at night when the land becomes cooler. Then the wind blows towards the warm, low-pressure area over the water.

Land and sea breezes are very local and affect only a narrow area along the coast.

Hills and valleys substantially distort the airflow associated with the prevailing pressure system and the pressure gradient. Strong up and down drafts and eddies develop as the air flows up over hills and down into valleys. Wind direction changes as the air flows around hills. Sometimes lines of hills and mountain ranges will act as a barrier, holding back the wind and deflecting it so that it flows parallel to the range. If there is a pass in the mountain range, the wind will rush through this pass as through a tunnel with considerable speed. The airflow can be expected to remain turbulent and erratic for some distance as it flows out of the hilly area and into the flatter countryside.

Daytime heating and nighttime cooling of the hilly slopes lead to day to night variations in the airflow. At night, the sides of the hills cool by radiation. The air in contact with them becomes cooler and therefore denser and it blows down the slope into the valley. This is a katabatic wind (sometimes also called a mountain breeze). If the slopes are covered with ice and snow, the katabatic wind will blow, not only at night, but also during the day, carrying the cold dense air into the warmer valleys. The slopes of hills not covered by snow will be warmed during the day. The air in contact with them becomes warmer and less dense and, therefore, flows up the slope. This is an anabatic wind (or valley breeze).

In mountainous areas, local distortion of the airflow is even more severe. Rocky surfaces, high ridges, sheer cliffs, steep valleys, all combine to produce unpredictable flow patterns and turbulence.

Air flowing across a mountain range usually rises relatively smoothly up the slope of the range, but, once over the top, it pours down the other side with considerable force, bouncing up and down, creating eddies and turbulence and also creating powerful vertical waves that may extend for great distances downwind of the mountain range. This phenomenon is known as a mountain wave. Note the up and down drafts and the rotating eddies formed downstream.

If the air mass has a high moisture content, clouds of very distinctive appearance will develop.

Cap Cloud. Orographic lift causes a cloud to form along the top of the ridge. The wind carries this cloud down along the leeward slope where it dissipates through adiabatic heating. The base of this cloud lies near or below the peaks of the ridge the top may reach a few thousand feet above the peaks.

Lenticular (Lens Shaped) Cloudsform in the wave crests aloft and lie in bands that may extend to well above 40,000 feet.

Rotor Cloudsform in the rolling eddies downstream. They resemble a long line of stratocumulus clouds, the bases of which lie below the mountain peaks and the tops of which may reach to a considerable height above the peaks. Occasionally these clouds develop into thunderstorms.

The clouds, being very distinctive, can be seen from a great distance and provide a visible warning of the mountain wave condition. Unfortunately, sometimes they are embedded in other cloud systems and are hidden from sight. Sometimes the air mass is very dry and the clouds do not develop.

The severity of the mountain wave and the height to which the disturbance of the air is affected is dependent on the strength of the wind, its angle to the range and the stability or instability of the air. The most severe mountain wave conditions are created in strong airflows that are blowing at right angles to the range and in stable air. A jet stream blowing nearly perpendicular to the mountain range increases the severity of the wave condition.

The mountain wave phenomenon is not limited only to high mountain ranges, such as the Rockies, but is also present to a lesser degree in smaller mountain systems and even in lines of small hills.

Mountain waves present problems to pilots for several reasons:

Vertical Currents. Downdrafts of 2000 feet per minute are common and downdrafts as great as 5000 feet per minute have been reported. They occur along the downward slope and are most severe at a height equal to that of the summit. An airplane, caught in a downdraft, could be forced to the ground.

Turbulence is usually extremely severe in the air layer between the ground and the tops of the rotor clouds.

Wind Shear. The wind speed varies dramatically between the crests and troughs of the waves. It is usually most severe in the wave nearest the mountain range.

Altimeter Error. The increase in wind speed results in an accompanying decrease in pressure, which in turn affects the accuracy of the pressure altimeter.

Icing. The freezing level varies considerably from crest to trough. Severe icing can occur because of the large supercooled droplets sustained in the strong vertical currents.

When flying over a mountain ridge where wave conditions exist:

(1) Avoid ragged and irregular shaped clouds—the irregular shape indicates turbulence.
(2) Approach the mountain at a 45-degree angle. It you should suddenly decide to turn back, a quick turn can be made away from the high ground.
(3) Avoid flying in cloud on the mountain crest (cap cloud) because of strong downdrafts and turbulence.
(4) Allow sufficient height to clear the highest ridges with altitude to spare to avoid the downdrafts and eddies on the downwind slopes.
(5) Always remember that your altimeter can read over 3000 ft. in error on the high side in mountain wave conditions.

A gust is a rapid and irregular fluctuation of varying intensity in the upward and downward movement of air currents. It may be associated with a rapid change in wind direction. Gusts are caused by mechanical turbulence that results from friction between the air and the ground and by the unequal heating of the earth's surface, particularly on hot summer afternoons.

A squall is a sudden increase in the strength of the wind of longer duration than a gust and may be caused by the passage of a fast moving cold front or thunderstorm. Like a gust, it may be accompanied by a rapid change of wind direction.

Diurnal (daily) variation of wind is caused by strong surface heating during the day, which causes turbulence in the lower levels. The result of this turbulence is that the direction and speed of the wind at the higher levels (e.g., 3000 feet) tends to be transferred to the surface. Since the wind direction at the higher level is parallel to the isobars and its speed is greater than the surface wind, this transfer causes the surface wind to veer and increase in speed.

At night, there is no surface heating and therefore less turbulence and the surface wind tends to resume its normal direction and speed. It backs and decreases. See VEERING AND BACKING section below for more info.

Friction between the moving air mass and surface features of the earth (hills, mountains, valleys, trees, buildings, etc.) is responsible for the swirling vortices of air commonly called eddies. They vary considerably in size and intensity depending on the size and roughness of the surface obstruction, the speed of the wind and the degree of stability of the air. They can spin in either a horizontal or vertical plane. Unstable air and strong winds produce more vigorous eddies. In stable air, eddies tend to quickly dissipate. Eddies produced in mountainous areas are especially powerful.

The bumpy or choppy up and down motion that signifies the presence of eddies makes it difficult to keep an airplane in level flight.

Dust devils are phenomena that occur quite frequently on the hot dry plains of mid-western North America. They can be of sufficient force to present a hazard to pilots of light airplanes flying at low speeds.

They are small heat lows that form on clear hot days. Given a steep lapse rate caused by cool air aloft over a hot surface, little horizontal air movement, few or no clouds, and the noonday sun heating flat arid soil surfaces to high temperatures, the air in contact with the ground becomes super-heated and highly unstable. This surface layer of air builds until something triggers an upward movement. Once started, the hot air rises in a column and draws more hot air into the base of the column. Circulation begins around this heat low and increases in velocity until a small vigorous whirlwind is created. Dust devils are usually of short duration and are so named because they are made visible by the dust, sand and debris that they pick up from the ground.

Dust devils pose the greatest hazard near the ground where they are most violent. Pilots proposing to land on superheated runways in areas of the mid-west where this phenomenon is common should scan the airport for dust swirls or grass spirals that would indicate the existence of this hazard.

Tornadoes are violent, circular whirlpools of air associated with severe thunderstorms and are, in fact, very deep, concentrated low-pressure areas. They are shaped like a tunnel hanging out of the cumulonimbus cloud and are dark in appearance due to the dust and debris sucked into their whirlpools. They range in diameter from about 100 feet to one half mile and move over the ground at speeds of 25 to 50 knots. Their path over the ground is usually only a few miles long although tornadoes have been reported to cut destructive swaths as long as 100 miles. The great destructiveness of tornadoes is caused by the very low pressure in their centers and the high wind speeds, which are reputed to be as great as 300 knots.

Wind speeds for aviation purposes are expressed in knots (nautical miles per hour). In the weather reports on US public radio and television, however, wind speeds are given in miles per hour while in Canada speeds are given in kilometers per hour.

In a discussion of wind direction, the compass point from which the wind is blowing is considered to be its direction. Therefore, a north wind is one that is blowing from the north towards the south. In aviation weather reports, area and aerodrome forecasts, the wind is always reported in degrees true. In ATIS broadcasts and in the information given by the tower for landing and take-off, the wind is reported in degrees magnetic.

The wind veers when it changes direction clockwise. Example: The surface wind is blowing from 270°. At 2000 feet it is blowing from 280°. It has changed in a right-hand, or clockwise, direction.

The wind backs when it changes direction anti-clockwise. Example: The wind direction at 2000 feet is 090° and at 3000 feet is 085°. It is changing in a left-hand, or anti-clockwise, direction.

In a descent from several thousand feet above the ground to ground level, the wind will usually be found to back and also decrease in velocity, as the effect of surface friction becomes apparent. In a climb from the surface to several thousand feet AGL, the wind will veer and increase.

At night, surface cooling reduces the eddy motion of the air. Surface winds will back and decrease. Conversely, during the day, surface heating increases the eddy motion of the air. Surface winds will veer and increase as stronger winds aloft mix to the surface. See DIURNAL VARIATIONS section above for more info.

Wind shear is the sudden tearing or shearing effect encountered along the edge of a zone in which there is a violent change in wind speed or direction. It can exist in a horizontal or vertical direction and produces churning motions and consequently turbulence. Under some conditions, wind direction changes of as much as 180 degrees and speed changes of as much as 80 knots have been measured.

The effect on airplane performance of encountering wind shear derives from the fact that the wind can change much faster than the airplane mass can be accelerated or decelerated. Severe wind shears can impose penalties on an airplane's performance that are beyond its capabilities to compensate, especially during the critical landing and take-off phase of flight.


In Cruising Flight

In cruising flight, wind shear will likely be encountered in the transition zone between the pressure gradient wind and the distorted local winds at the lower levels. It will also be encountered when climbing or descending through a temperature inversion and when passing through a frontal surface. Wind shear is also associated with the jet stream. Airplanes encountering wind shear may experience a succession of updrafts and downdrafts, reductions or gains in headwind, or windshifts that disrupt the established flight path. It is not usually a major problem because altitude and airspeed margins will be adequate to counteract the shear's adverse effects. On occasion, however, the wind shear may be severe enough to cause an abrupt increase in load factor, which might stall the airplane or inflict structural damage.


Near the Ground

Wind shear, encountered near the ground, is more serious and potentially very dangerous. There are four common sources of low level wind shear: thunderstorms, frontal activity, temperature inversions and strong surface winds passing around natural or manmade obstacles.

Frontal Wind Shear. Wind shear is usually a problem only in fronts with steep wind gradients. If the temperature difference across the front at the surface is 5°C or more and if the front is moving at a speed of about 30 knots or more, wind shear is likely to be present. Frontal wind shear is a phenomenon associated with fast moving cold fronts but can be present in warm fronts as well.


Thunderstorms. Wind shear, associated with thunderstorms, occurs as the result of two phenomena, the gust front and downbursts. As the thunderstorm matures, strong downdrafts develop, strike the ground and spread out horizontally along the surface well in advance of the thunderstorm itself. This is the gust front. Winds can change direction by as much as 180° and reach speeds as great as 100 knots as far as 10 miles ahead of the storm. The downburst is an extremely intense localized downdraft flowing out of a thunderstorm. The power of the downburst can exceed aircraft climb capabilities. The downburst (there are two types of downbursts: macrobursts and microbursts) usually is much closer to the thunderstorm than the gust front. Dust clouds, roll clouds, intense rainfall or virga (rain that evaporates before it reaches the ground) are due to the possibility of downburst activity but there is no way to accurately predict its occurrence.


Temperature Inversions. Overnight cooling creates a temperature inversion a few hundred feet above the ground that can produce significant wind shear, especially if the inversion is coupled with the low-level jet stream.

As a nocturnal inversion develops, the wind shear near the top of the inversion increases. It usually reaches its maximum speed shortly after midnight and decreases in the morning as daytime heating dissipates the inversion. This phenomenon is known as the low-level nocturnal jet stream. The low level jet stream is a sheet of strong winds, thousands of miles long, hundreds of miles wide and hundreds of feet thick that forms over flat terrain such as the prairies. Wind speeds of 40 knots are common, but greater speeds have been measured. Low level jet streams are responsible for hazardous low level shear.

As the inversion dissipates in the morning, the shear plane and gusty winds move closer to the ground, causing windshifts and increases in wind speed near the surface.


Surface Obstructions. The irregular and turbulent flow of air around mountains and hills and through mountain passes causes serious wind shear problems for aircraft approaching to land at airports near mountain ridges. Wind shear is a phenomenon associated with the mountain wave. Such shear is almost totally unpredictable but should be expected whenever surface winds are strong.

Wind shear is also associated with hangars and large buildings at airports. As the air flows around such large structures, wind direction changes and wind speed increases causing shear.

Wind shear occurs both horizontally and vertically. Vertical shear is most common near the ground and can pose a serious hazard to airplanes during take-off and landing. The airplane is flying at lower speeds and in a relatively high drag configuration. There is little altitude available for recovering and stall and maneuver margins are at their lowest. An airplane encountering the wind shear phenomenon may experience a large loss of airspeed because of the sudden change in the relative airflow as the airplane flies into a new, moving air mass. The abrupt drop in airspeed may result in a stall, creating a dangerous situation when the airplane is only a few hundred feet off the ground and very vulnerable.

Narrow bands of exceedingly high speed winds are known to exist in the higher levels of the atmosphere at altitudes ranging from 20,000 to 40,000 feet or more. They are known as jet streams. As many as three major jet streams may traverse the North American continent at any given time. One lies across Northern Canada and one across the U.S. A third jet stream may be as far south as the northern tropics but it is somewhat rare. A jet stream in the mid latitudes is generally the strongest.

The jet stream appears to be closely associated with the tropopause and with the polar front. It typically forms in the break between the polar and the tropical tropopause where the temperature gradients are intensified. The mean position of the jet stream shears south in winter and north in summer with the seasonal migration of the polar front. Because the troposphere is deeper in summer than in winter, the tropopause and the jets will nominally be at higher altitudes in the summer.

Long, strong jet streams are usually also associated with well-developed surface lows beneath deep upper troughs and lows. A low developing in the wave along the frontal surface lies south of the jet. As it deepens, the low moves near the jet. As it occludes, the low moves north of the jet, which crosses the frontal system, near the point of occlusion. The jet flows roughly parallel to the front. The subtropical jet stream is not associated with fronts but forms because of strong solar heating in the equatorial regions. The ascending air turns poleward at very high levels but is deflected by the Coriolis force into a strong westerly jet. The subtropical jet predominates in winter.

The jet streams flow from west to east and may encircle the entire hemisphere. More often, because they are stronger in some places than in others, they break up into segments some 1000 to 3000 nautical miles long. They are usually about 300 nautical miles wide and may be 3000 to 7000 feet thick. These jet stream segments move in an easterly direction following the movement of pressure ridges and troughs in the upper atmosphere.

Winds in the central core of the jet stream are the strongest and may reach speeds as great as 250 knots, although they are generally between 100 and 150 knots. Wind speeds decrease toward the outer edges of the jet stream and may be blowing at only 25 knots there. The rate of decrease of wind speed is considerably greater on the northern edge than on the southern edge. Wind speeds in the jet stream are, on average, considerably stronger in winter than in summer.


Clear Air Turbulence. The most probable place to expect Clear Air Turbulence (CAT) is just above the central core of the jet stream near the polar tropopause and just below the core. Clear air turbulence does not occur in the core. CAT is encountered more frequently in winter when the jet stream winds are strongest. Nevertheless, CAT is not always present in the jet stream and, because it is random and transient in nature, it is almost impossible to forecast.

Clear air turbulence may be associated with other weather patterns, especially in wind shear associated with the sharply curved contours of strong lows, troughs and ridges aloft, at or below the tropopause, and in areas of strong cold or warm air advection. Mountain waves create severe CAT that may extend from the mountain crests to as high as 5000 feet above the tropopause. Since severe CAT does pose a hazard to airplanes, pilots should try to avoid or minimize encounters with it. These rules of thumb may help avoid jet streams with strong winds (150 knots) at the core. Strong wind shears are likely above and below the core. CAT within the jet stream is more intense above and to the lee of mountain ranges. If the 20-knot isotachs (lines joining areas of equal wind speeds) are closer than 60 nautical miles on the charts showing the locations of the jet stream, wind shear and CAT are possible.

Curving jet streams are likely to have turbulent edges, especially those that curve around a deep pressure trough. When moderate or severe CAT has been reported or is forecast, adjust speed to rough air speed immediately on encountering the first bumpiness or even before encountering it to avoid structural damage to the airplane.

The areas of CAT are usually shallow and narrow and elongated with the wind. If jet stream turbulence is encountered with a tail wind or head wind, a turn to the right will find smoother air and more favorable winds. If the CAT is encountered in a crosswind, it is not so important to change course as the rough area will be narrow.

Click above image(s) for larger image


2 Answers 2

Sorry, no drawings. But the sources have photos of examples, and names of actual locations. You would need a seriously detailed drawing/photo to describe all of these features.

Ablation zone - The area of a glacier where yearly melting meets or exceeds the annual snow fall. Reference: Ablation zone

Aiguille - [French - needle] A tall, narrow spire of rock. See pinnacle, spire, needle.

Alluvial fan - A cone of sediment deposited at an abrupt change of slope for example, where a post-glacial stream meets the flat floor of a U-shaped valley. Alluvial fans are also common in arid regions where streams flowing off escarpments may periodically carry large loads of sediment during flash floods. Example: Alluvial fan

Alp - A gentle slope above the steep sides of a glaciated valley, often used for summer grazing. See also transhumance. Definition: Alp

Arete - [French (arête) - edge or ridge] 1. A narrow ridge. 2. In glaciology, a narrow ridge remaining after glacial erosion from both sides. 3. In rock climbing, a vertical ridge or junction of walls at a convex angle in a rock face. Example: Arête

Barchan - [Kazakh] - An arc-shaped dune. Mostly used for sand dunes but sometimes applied to snow dunes as well. Example: Barchan

Bergschrund - [German - hill-gap] - A crevasse that forms the upper edge of a glacier, separating it from the fixed ice-cap above it. Compare "moat". Example: Bergschrund

Butte - [French] A steep-sided, flat-topped hill, smaller than a "mesa". Example: Butte

Buttress - A prominent feature that juts out from a rock or mountain. Example: Buttress

Caldera - [Spanish - cooking pot] A large crater formed by the collapse of the summit cone of a volcano during an eruption. The caldera may contain subsidiary cones built up by subsequent eruptions, or a crater lake if the volcano is extinct or dormant. Example: Caldera

Canyon - [Spanish, cañón] - A canyon or gorge is a deep cleft between escarpments or cliffs resulting from the erosive activity of a river over geologic timescales. Also gorge. Example: Canyon

Chimney - A rock cleft with vertical sides mostly parallel, large enough to fit the climber's body into. To climb such a structure, the climber often uses his head, back and feet to apply opposite pressure on the vertical walls. Also Hoodoo, tent rock, fairy chimney, or earth pyramid. Example: Hoodoo

Cirque - [French - circus] A bowl-shaped valley high on a mountain, usually of glacial origin. Synonyms: cwm (Gaelic), corrie (Scots Gaelic). Example: Cirque

Cleaver - A cleaver is a type of arête that separates a unified flow of glacial ice from its uphill side into two glaciers flanking, and flowing parallel to, the ridge. Cleaver gets its name from the way it resembles a meat cleaver slicing meat into two parts.

Cliff - A steep rock face between land and sea, the profile of which is determined largely by the nature of the coastal rocks. For example, resistant rocks such as granite (e.g. at Land's End, England) will produce steep and rugged cliffs. Example: Cliff

Col - [Latin - neck] the low point on a ridge joining two peaks. Glaciologists reserve this term for gaps of glacial origin, but others use it much more generally. Example: Col

Coombe or Combe - See dry valley.

Cornice - [French, from "horn"] - Overhanging build-up of snow formed by wind passing sideways over a ridge or cliff. Example: Snow cornice

Corrie - A bowl-shaped hollow on a mountainside in a glaciated region the area where a valley glacier originates. In glacial times the corrie contained an icefi eld, which in cross section appears as in diagram a above. The shape of the corrie is determined by the rotational erosive force of ice as the glacier moves downslope. See also cirque or cwm.

Couloir - [French - passage, corridor] a steep gorge or gully in a mountainside. Couloirs are good places to find uninterrupted snow and ice. Example: Couloir

Crag - [Gaelic] - a rocky outcrop

Crag and tail - Also cragg or (Scotland) craig. A feature of lowland glaciation, where a resistant rock outcrop withstands erosion by a glacier and remains as a feature after the Ice Age. Rocks of volcanic or metamorphic origin are likely to produce such a feature. As the ice advances over the crag, material will be eroded from the face and sides and will be deposited as a mass of boulder clay and debris on the leeward side, thus producing a 'tail'. Example: Crag and tail

Crevasse - [French - crevice] - A crack in a glacier. Formed by stresses on the moving ice. A major navigational difficulty for mountaineers, and a major hazard when hidden by recent snow. Example: Crevasse

Cwm - [Welsh - valley] see "cirque". Example: Western Cwm

Dihedral - [Greek - two planes] - In rock climbing, a junction of two vertical walls at a concave angle (compare arete). In geometry, the angle between two planes. Also, Dièdre. Example: Dihedral

Dièdre - See Dihedral.

Dike - A dike or dyke, in geological usage, is a sheet of rock that formed in a fracture in a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma intrudes into a crack then crystallizes as a sheet intrusion, either cutting across layers of rock or through an unlayered mass of rock. Clastic dikes are formed when sediment fills a pre-existing crack. Example: Dike

Dip Slope - The gentler of the two slopes on either side of an escarpment crest the dip slope inclines in the direction of the dipping strata the steep slope in front of the crest is the scarp slope. Example Dip slope

Dome - A peak having that shape. Example: Dome

Drumlin - [Gaelic - ridge] - a hill formed from glacial debris. See also "moraine". Example: Drumlin

Dry valley - Also coombe. A feature of limestone and chalk country, where valleys have been eroded in dry landscapes. Example: Dry valley

Escarpment - steep slope or long cliff that forms as an effect of faulting or erosion and separates two relatively level areas of differing elevations. Usually escarpment is used interchangeably with scarp (from the Italian scarpa, shoe). But some sources differentiate the two terms, where escarpment refers to the margin between two landforms, while scarp is synonymous with a cliff or steep slope. The surface of the steep slope is called a scarp face. This (escarpment) is a ridge which has a gentle (dip) slope on one side and a steep (scarp) slope on the other side. Example: Escarpment

Fault - A fracture in the Earth’s crust on either side of which the rocks have been relatively displaced. Faulting occurs in response to stress in the Earth’s crust the release of this stress in fault movement is experienced as an earthquake. See also rift valley. Example: Fault

Felsenmeer - [German - sea of rock] - Terrain of fractured rock formed in place by frost action. Compare "talus". Also, Block Field, Bolder Field, Stone Field. Example: Blockfield

Fold - A bending or buckling of once horizontal rock strata. Many folds are the result of rocks being crumpled at plate boundaries (see plate tectonics), though earthquakes can also cause rocks to fold, as can igneous intrusions. Example: Fold

Fold mountains - Mountains which have been formed by large-scale and complex folding. Studies of typical fold mountains (the Himalayas, Andes, Alps and Rockies) indicate that folding has taken place deep inside the Earth’s crust and upper mantle as well as in the upper layers of the crust. Example: Fold mountains

Gendarme - [French - man-at-arms] A steep-sided rock formation along a ridge (metaphorically "guarding" the summit). Example: Gendarme

Glacier - [French] - Year-round ice covering a large area. Formed from snowfall, glaciers will slide very slowly downhill.

Gorge - See canyon.

Gully - [Middle French - "throat"] - a channel caused by erosion, especially by water running down a slope. The distinction between "gully" and "valley" or "canyon" is one of scale - a gully is usually less than a hundred meters in width. (It is also at least a meter wide anything smaller would be a ditch or runnel.) Example: Gully Canyon Runnel

Hanging valley - A valley whose lower end is high on a sheer wall of a larger valley into which it flows. Example: Hanging Valley

Headwall - vertical ("wall") or near-vertical section of slope at the uphill end ("head") of a valley, ravine, cirque, etc. Example: Headwall

Highpoint - The point of highest elevation in a given area, eg country, state, or county. A highpoint need not be a summit (or even a peak): The highpoint of the state of Connecticut is on the slopes of Mt Frissel, whose summit is outside the state.

Horn - a peak having that shape. In glaciology, a horn is defined as the sheer-sided peak remaining after glaciers have removed at least three sides.

Inselberg - [German - "island mountain"] - a mountain with no other mountains nearby. Examples: List of inselbergs

Interlocking spurs - Obstacles of hard rock round which a river twists and turns in a V-shaped valley. Erosion is pronounced on the concave banks, and this ultimately causes the development of spurs which alternate on either side of the river and interlock as shown in the diagram. Example: Interlocking spur

Klettersteig - [German] - See Via Ferreta.

Knob - A peak or hill having that shape.

Knoll - small round hill.

Krummholz - [German - "twisted wood"] - bonsai-like dwarf trees that grow at treeline. Example: Krummholz

Lahar - [Java - flowing lava] - A landslide of pyroclastic debris mixed with water down the sides of a volcano, caused either by heavy rain or the heat of the volcano melting snow and ice. Example: Lahar

Ledge - A narrow, (more-or-less) flat spot along an otherwise (mostly) vertical face. Synonym: "shelf".

Massif - [French - massive] - a range or plateau a "mass" of peaks or mountains. Carries an implication that the peaks or mountains are bunched together, but not in a neat line. Borrowed from French. Like "range", can be applied on extremely varied scales, from "Massif Central" to "Massif du Mont Blanc." Examples: Massif

Moat - Gap along the side of a glacier, separating it from the rock of the valley wall. Compare "bergschrund".

Monadnock - [Abenaki - "Lone Mountain" the name of a mountain in New Hampshire, USA] - "inselberg".

Moraine - [Savoyard French - hill] - A mound or ridge of dirt, rock, etc deposited by the edge of a glacier. See also "drumlin". Example: Moraine

Mesa - [Spanish - table] - a large formation having steep sides and a large flat top. Example: Mesa

Mountain - Not easily defined. Some governments or hiking clubs will define a mountain as having a minimum elevation, or a minimum prominence, but these standards vary widely.

Needle - A tall, narrow spire of rock. See pinnacle, spire, aiguille.

Nunatak - [Inuit - lonely peak] - An ice-free peak that sticks up through a glacier. Example: Nunatak

Pass - Any route from one valley, over higher ground to another valley. Usually, a relatively low point along a ridge. Many regional synonyms, such as "notch" in New England. Example: Mountain pass

Peak, Summit - This is the top of the mountain and a climber’s ultimate goal. In theory, every mountain has exactly one summit.

The difference between a peak and summit is that mountains can have multiple peaks, and definition is usually localized. A peak is a point that's higher than all other adjacent points. There may be some higher point not far away, but if you can't get there without going downhill first, you're standing on a peak.

In common usage, a "peak" is pointy, otherwise it may be called a "knob", "crag", "bald", or "dome".

Penitentes - [Spanish - penitents] - Spiky ice formations caused by uneven evaporation/melting of ice in sunlight. See also sun cups. Example: Penitente

Pinnacle - A pinnacle, tower, spire, needle or natural tower in geology is an individual column of rock, isolated from other rocks or groups of rocks, in the shape of a vertical shaft or spire. See needle, spire, aiguille. Example: Pinnacle

Plateau - [French - serving plate] - any area that is higher than (some of) its surroundings and fairly flat when considered from sufficient distance. Example: Plateau

Point - 1. Any location. 2. A small peninsula, or a formation resembling one. 3. A peak, prominence, or spur not considered worthy of the name "peak", or simply not yet named. In the absence of any other name, a peak or benchmark may be referred to as "point xxx", where xxx is its elevation.

Prominence - [Latin - forward projection] 1. The quality of rising above or projecting beyond one's neighbors. 2. A peak or outcrop. 3. A measure of how far a peak rises above its neighbors: the minimum vertical distance one must descend in order to travel (on the ground) from a peak to any higher peak. Example: Prominence

Range - A range is a group of mountains.

Roche moutonnée - An outcrop of resistant rock sculpted by the passage of a glacier. Also sheepback. Example: Roche moutonnée

Saddle - A formation having that shape: high and broad at each end, lower and narrower in the middle. Example: Saddle

Sastrugi - [Russian - grooves] - ripple-like forms with sharp corners formed in hard, windswept snow. Compare "barchan". Example: Sastrugi

Scarp slope - The steeper of the two slopes which comprise an escarpment of inclined strata. Compare dip slope.

Scree - [Nordic] - A surface consisting of small loose rocks which have slid from above and are likely to slide again when stepped upon. Example: Scree

Sea level - Fictional surface formed by the average height of the oceans, ignoring tidal cycles, weather, etc, and extended underneath the land to form a continous surface. This surface is not spherical. Commonly used approximations include "ellipsoids" (slightly-squashed spheres) and "geoids" (bumpier) the latter reflect variations in the strength of gravity in different locations. In many places the various kinds of "sea level" differ from each other by tens of meters, so next time you hear someone recite the altitude of Peak X down to the nearest centimeter, make sure you ask what "reference datum" they're using.

Seif dune - A linear sand dune, the ridge of sand lying parallel to the prevailing wind direction. The eddying movement of the wind keeps the sides of the dune steep. Example: Longitudinal dunes

Separation - the horizontal distance between two points. Sometimes used in deciding whether two points "count" as separate peaks or mountains.

Serac - [French - Cheese curd] - A large block or peak of glacier ice which is separated by crevasses from the main mass of its glacier, especially a block that is tilted, upthrust, or overhanging. Example: Serac

Shoulder - a lateral protrusion on a mountain, or a point on the mountain where the slope changes, forming a convex shape.

Slope - This is the side of the mountain. See "Snowline". Example: Slope

Snowline - the elevation above which snow remains on the ground year-round, ie the lower boundary of a permanent snowcap. Sometimes also used to designate the lower elevation boundary of merely seasonal snowfields. Example: Snowline

Spire - a tall and narrow rock formation, resembling a steeple. See pinnacle, needle, aiguille.

Spur - [from riding spur, a pointy tool for kicking a horse] - a part of a mountain that projects outward, laterally away from the main body. Example: Spur

Sun cups - uneven surface of snow or ice caused by uneven evaporation/melting in sunlight. See also "penitentes".

Syncline - A trough in folded strata the opposite of anticline. See fold. Example: Syncline

Talus - [French - earthwork] - Jumble of boulders at the base of a cliff from which they've fallen. Compare "felsenmeer". See "scree".

Treeline - the elevation above which trees cannot grow. Varies with latitude, soil, and exposure to weather (especially wind). In most places trees don't suddenly cease but rather become gradually more dwarfish - see "krummholz". More-precise definitions (eg, trees below some particular height) may be used for various purposes but I am not aware of a uniform standard.

U-shaped valley - A glaciated valley, characteristically straight in plan and U-shaped in cross section. See diagram. Compare V-shaped valley. Example: U-shaped valley

V-shaped valley - A narrow, steep-sided valley made by the rapid erosion of rock by streams and rivers. It is V-shaped in cross-section. Compare U-shaped valley.

Valley - The whole trough or dip between two mountains is called a valley. Example: Valley

Verglas - [French - glassy ice] - thin, clear ice formed by the freezing of rain or meltwater on a hard, smooth surface (ie, rock). Extremely slippery, and sometimes too thin to hold a crampon or ice axe.

Via Ferrata - [Spanish] A route on a mountain where the safety is provided by steel ropes or chains, permanently fixated to the rock. The progression is often aided by artificial steps or ladders. Typically found in the Alps, also called Klettersteig. Example: Via ferrata

Yardang - [Turkish - steep bank] - Long, roughly parallel ridges of rock in arid and semi-arid regions. The ridges are undercut by wind erosion and the corridors between them are swept clear of sand by the wind. The ridges are oriented in the direction of the prevailing wind. Example: Yardang

Zeugen - Pedestal rocks in arid regions wind erosion is concentrated near the ground, where corrasion by wind-born sand is most active. This leads to undercutting and the pedestal profile emerges.


Weather References

Fire weather notes for slash burning, Alberta Forest Service, 1985.

Andrews, Patricia L, Modeling Wind Adjustment Factor and Midflame Wind Speed for Rothermel’s Surface Fire Spread Model, General Technical Report RMRS-GTR-266, USDA Forest Service. Rocky Mountain Research Station, 2012.

Bishop, Jim, Technical Background of the FireLine Assessment Method (FLAME), RMRS-P-46CD. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. CD-ROM. pages 27-74.

Haines, D.A., A Lower Atmospheric Severity Index for Wildland Fire, National Weather Digest. Vol 13. No. 2:23-27, 1988.

Latham, Don J. and Rothermel, Richard C., Probability of Fire-Stopping Precipitation Events, USDA Forest Service, Research Note INT-410 page 8, 1993.

Schroeder, Mark J. and Buck, Charles C., Fire Weather: A Guide For Application of Meteorological Information to Forest Fire Control Operations, USDA Forest Service Agricultural Handbook 360, pages 85-126, 1970.

Werth, Paul and Ochoa, Richard, The Haines Index and Idaho Wildfire Growth, Fire Management Notes, 1990.

Werth, John and Werth, Paul, Haines Index Climatology for the Western United States, NOAA National Weather Service Western Region Technical Attachment No. 97-17, 1997.

Werth, Paul A., Potter, Brian E., Clements, Craig B., Finney, Mark A., Goodrick, Scott L., Alexander, Martin E., Cruz, Miguel G., Forthofer, Jason A., McAllister, Sara S., Synthesis of Knowledge of Extreme Fire Behavior: Volume I for Fire Managers, U.S. Department of Agriculture, Forest Service, Pacific Northwest Research Station, 2011.

Whiteman, C. David, Mountain Meteorology: Fundamentals and Applications, Oxford University Press, 2000.


Chapter 1 Geomorphometry: A Brief Guide

Geomorphometry is the science of quantitative land-surface analysis. It evolved directly from geomorphology and quantitative terrain analysis, two disciplines that originated in 19th century geometry, physical geography, and the measurement of mountains. Modern geomorphometry addresses the refinement and processing of elevation data, description and visualization of topography, and a wide variety of numerical analyses. It focuses on the continuous land-surface, although it also includes the analysis of landforms, discrete features, such as watersheds. The operational goal of geomorphometry is extraction of measures and spatial features from digital topography. Geomorphometry supports countless applications in the Earth sciences, civil engineering, military operations, and entertainment. Geomorphometric analysis commonly entails five steps: Sampling a surface, generating and correcting a surface model, calculating land-surface parameters or objects, and applying the results. The three classes of parameters and objects include both landforms and pointmeasures, such as slope and curvature. Landform elements are fundamental spatial units having uniform properties. Complex analyses may combine several parameter maps and incorporate non-topographic data. The procedure that extracts most land-surface parameters and objects from a digital elevation model (DEM) is the neighborhood operation. Because parameters can be generated by different algorithms or sampling strategies, and vary with spatial scale, no DEM-derived map is definitive.


Identifying south facing mountain land, above an elevation, within a slope range, less than fixed distance from major roadways - Geographic Information Systems

Pseudotsuga menziesii (Mirb.) Franco

Richard K. Hermann and Denis P. Lavender

Douglas-fir (Pseudotsuga menziesii), also called red-fir, Oregon-pine, Douglas-spruce, and piño Oregon (Spanish), is one of the world's most important and valuable timber trees. It has been a major component of the forests of western North America since the mid-Pleistocene (30). Although the fossil record indicates that the native range of Douglas-fir has never extended beyond western North America, the species has been successfully introduced in the last 100 years into many regions of the temperate forest zone (31). Two varieties of the species are recognized: P. menziesii (Mirb.) Franco var. menziesii, called coast Douglas-fir, and P. menziesii var. glauca (Beissn.) Franco, called Rocky Mountain or blue Douglas-fir.

Habitat

Native Range

The latitudinal range of Douglas-fir is the greatest of any commercial conifer of western North America. Its native range, extending from latitude 19° to 55° N., resembles an inverted V with uneven sides. From the apex in central British Columbia, the shorter arm extends south along the Pacific Coast Ranges for about 2200 km (1,367 mi) to latitude 34° 44' N., representing the range of the typical coastal or green variety, menziesii the longer arm stretches along the Rocky Mountains into the mountains of central Mexico over a distance of nearly 4500 km (2,796 mi), comprising the range of the other recognized variety, glauca - Rocky Mountain or blue. Nearly pure stands of Douglas-fir continue south from their northern limit on Vancouver Island through western Washington, Oregon, and the Klamath and Coast Ranges of northern California as far as the Santa Cruz Mountains. In the Sierra Nevada, Douglas-fir is a common part of the mixed conifer forest as far south as the Yosemite region. The range of Douglas-fir is fairly continuous through northern Idaho, western Montana, and northwestern Wyoming. Several outliers are present in Alberta and the eastern-central parts of Montana and Wyoming, the largest being in the Bighorn Mountains of Wyoming. In northeastern Oregon, and from southern Idaho south through the mountains of Utah, Nevada, Colorado, New Mexico, Arizona, extreme western Texas, and northern Mexico, the distribution becomes discontinuous.


- The native range of Douglas-fir.

Climate

Douglas-fir grows under a wide variety of climatic conditions (table 1). The coastal region of the Pacific Northwest has a maritime climate characterized by mild, wet winters and cool, relatively dry summers, a long frost-free season, and narrow diurnal fluctuations of temperature (6° to 8° C 43° to 46° F). Precipitation, mostly as rain, is concentrated in the winter months. Climate in the Cascade Range and Sierra Nevada tends to be more severe.

Table 1- Climatic data for five regional subdivisions of the range of Douglas-fir (6,62)
Mean temperature Mean precipitation
Region July January Frost-free period Annual Snow fall
°C °C days mm cm
Pacific Northwest
Coastal 20 to 27 -2 to 3 195 to 260 760 to 3400 0 to 60
Cascades and
Sierra Nevada 22 to 30 -9 to 3 80 to 180 610 to 3050 10 to 300
Rocky Mountains
Northern 14 to 20 -7 to 3 60 to 120 560 to 1020 40 to 580
Central 14 to 21 -9 to -6 65 to 130 360 to 610 50 to 460
Southern 7 to 11 0 to 2 50 to 110 410 to 760 180 to 300
°F °F days in in
Pacific Northwest
Coastal 68 to 81 28 to 37 195 to 260 34 to 134 0 to 24
Cascades and
Sierra Nevada 72 to 86 15 to 28 80 to 180 24 to 120 4 to 120
Rocky Mountains
Northern 57 to 68 19 to 28 60 to 120 22 to 40 16 to 320
Central 57 to 70 16 to 22 65 to 130 14 to 24 20 to 180
Southern 45 to 52 32 to 36 50 to 110 16 to 30 70 to 120

Altitude has a significant effect on local climate. In general, temperature decreases and precipitation increases with increasing elevation on both western and eastern slopes of the mountains. Winters are colder, frost-free seasons are shorter, and diurnal fluctuations of temperature are larger (10° to 16° C 50° to 61° F). Much of the precipitation is snow. In the northern Rocky Mountains, Douglas-fir grows in a climate with a marked maritime influence. Mild continental climate prevails in all seasons, except midsummer. Precipitation is evenly distributed throughout the year, except for a dry period in July and August. In the central Rocky Mountains, the climate is continental. Winters are long and severe summers are hot and in some parts of the region, very dry. Annual precipitation, higher on the western sides of the mountains, is mainly snow. Rainfall patterns for the southern Rocky Mountains generally show low winter precipitation east of the Continental Divide but high precipitation during the growing season. West of the Continental Divide, the rainfall is more evenly divided between winter and summer. Frost may occur in any month in the northern part of the range. Length of frost-free periods, however, varies within the central and southern Rocky Mountain regions, even at the same elevations.

Soils and Topography

The variety menziesii of Douglas-fir reaches its best growth on well-aerated, deep soils with a pH range from 5 to 6. It will not thrive on poorly drained or compacted soils. Soils in the coastal belt of northern California, Oregon, and Washington originated chiefly from marine sandstones and shales with scattered igneous intrusions. These rocks have weathered deeply to fine-textured, well-drained soils under the mild, humid climate of the coast. Surface soils are generally acid, high in organic matter and total nitrogen, and low in base saturation. Soils in the Puget Sound area and in southwestern British Columbia are almost entirely of glacial origin. Soils farther inland within the range of the variety menziesii are derived from a wide variety of parent materials. These include metamorphosed sedimentary material in the northern Cascades and igneous rocks and formations of volcanic origin in the southern Cascades.

Depth of soils ranges from very shallow on steep slopes and ridgetops to deep in deposits of volcanic origin and residual and colluvial materials. Texture varies from gravelly sands to clays. Surface soils are in general moderately acid. Their organic matter content varies from moderate in the Cascade Range to high in portions of the Coast Range and Olympic Peninsula. Total nitrogen content varies considerably but is usually low in soils of glacial origin. Great soil groups characteristic of the range of coastal Douglas-fir include Haplohumults (Reddish Brown Lateritics) of the order Ultisols, Dystrochrepts (Brown Lateritics), Haplumbrepts (Sols Bruns Acides) of the order Inceptisols, Haplorthods (Western Brown Forest soils) of the order Spodosols, Xerumbrepts (Brown Podzolic soils), and Vitrandepts (Regosols) (63).

Soils within the range of Rocky Mountain Douglas-fir originated also from a considerable array of parent materials. In south-central British Columbia, eastern Washington, and northern Idaho, soils vary from basaltic talus to deep loess with volcanic ash to thin residual soil over granitic or sedimentary rocks. They are mostly Vitrandepts and Xerochrepts. Parent materials in Montana and Wyoming consist of both igneous and sedimentary rocks, and locally of glacial moraines. Soils derived from noncalcareous substrates are variable in texture but consistently gravelly and acidic. A significant portion of the sedimentary rocks is limestone, which gives rise to neutral or alkaline soils ranging in texture from gravelly loams to gravelly silts. Limestones often weather into soils that are excessively well drained. Soils are Cryoboralfs of the order Alfisols, and Cryandepts and Cryochrepts of the order Inceptisols. Soils in the central and southern Rocky Mountains are very complex. They developed from glacial deposits, crystalline granitic rocks, conglomerates, sandstones, and, in the Southwest, limestones. These soils are Alfisols (Gray Wooded soils), Mollisols (Brown Forest soils), Spodosols (Brown Podzolic soils, Podzols), and Entisols (2,46).

Altitudinal distribution of both varieties of Douglas-fir (menziesii and glauca ) increases from north to south, reflecting the effect of climate on distribution of the species. The principal limiting factors are temperature in the north of the range and moisture in the south. Consequently, Douglas-fir is found mainly on southerly slopes in the northern part of its range, and on northerly exposures in the southern part. At high elevations in the southern Rocky Mountains, however, Douglas-fir grows on the sunny slopes and dry rock exposures (56).

Generally, the variety glauca grows at considerably higher altitudes than the coastal variety of comparable latitude. Altitudinal limit for Douglas-fir in central British Columbia is about 760 m (2,500 ft) but rises to 1250 m (4,100 ft) on Vancouver Island. In Washington and Oregon, the species generally occurs from sea level to 1520 m (5,000 ft), although locally it may occur higher. In the southern Oregon Cascades and in the Sierra Nevada, the altitudinal range is between 610 and 1830 m (2,000 and 6,000 ft). In river valleys and canyon bottoms, the species may occasionally occur at elevations of 240 to 270 m (800 to 900 ft). Near the southern limit of its range in the Sierra Nevada, the species grows to elevations of 2300 m (7,500 ft). The inland variety grows at elevations from 550 to 2440 m (1,800 to 8,000 ft) in the northern part of its range. In the central Rocky Mountains, Douglas-fir grows mostly at elevations between 1830 and 2590 m (6,000 and 8,000 ft), and in the southern Rocky Mountains, between 2440 and 2900 m (8,000 and 9,500 ft). In some localities in southern and central Arizona, Douglas-fir may be found as low as 1550 m (5,100 ft) in canyon bottoms. The highest elevation at which Douglas-fir grows in the Rocky Mountains is 3260 m (10,700 ft) on the crest of Mount Graham in southeastern Arizona.

Associated Forest Cover

Periodic recurrence of catastrophic wildfires created vast, almost pure stands of coastal Douglas-fir throughout its range north of the Umpqua River in Oregon. Although logging has mainly eliminated the original old-growth forest, clearcutting combined with slash burning has helped maintain Douglas-fir as the major component in second-growth stands. Where regeneration of Douglas-fir was only partially successful or failed, red alder (Alnus rubra) has become an associate of Douglas-fir or has replaced it altogether.

Rocky Mountain Douglas-fir grows in extensive pure stands, uneven- and even-aged, in southern Idaho and northern Utah and in western Montana as a broad belt between ponderosa pine and spruce-fir zones. At high elevations or northerly latitudes, more cold-tolerant mountain hemlock (Tsuga mertensiana), whitebark pine (Pinus albicaulis), true firs (Abies spp. ), Engelmann spruce (Picea engelmannii), western white pine (Pinus monticola), and lodgepole pine (Pinus contorta) gradually replace Douglas-fir. Douglas-fir yields to ponderosa pine (P. ponderosa), incense-cedar (Libocedrus decurrens), Oregon white oak Quercus garryana), California black oak (Q. kelloggii), canyon live oak (Q. chrysolepis), and interior live oak (Q. wislizeni) on droughty sites, and to western redcedar (Thuja plicata), maples (Acer spp. ), red alder, black cottonwood (Populus trichocarpa), and other broad-leaved species on poorly drained sites.

Toward the fog belt of the Pacific coast, Douglas-fir gives way to Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), and western redcedar. The variety menziesii is a major component of four forest cover types (20): Pacific Douglas-Fir (Society of American Foresters Type 229), Douglas-Fir-Western Hemlock (Type 230), Port Orford-Cedar (Type 231), and Pacific Ponderosa Pine-Douglas-Fir (Type 244). It is a minor component of the following types:

221 Red Alder
223 Sitka Spruce
224 Western Hemlock
225 Western Hemlock-Sitka Spruce
226 Coastal True Fir-Hemlock
227 Western Redcedar-Western Hemlock
228 Western Redcedar
232 Redwood
233 Oregon White Oak
234 Douglas-Fir-Tanoak-Pacific Madrone

The variety glauca is a principal species in three forest cover types: Interior Douglas-Fir (Type 210), Western Larch (Type 212), and Grand Fir (Type 213). It is a minor species in five types: Engelmann Spruce-Subalpine Fir (Type 206), White Fir (Type 211), Western White Pine (Type 215), Aspen (Type 217), and Lodgepole Pine (Type 218).

Wherever Douglas-fir grows in mixture with other species, the proportion may vary greatly, depending on aspect, elevation, kind of soil, and the past history of an area, especially as it relates to fire. This is particularly true of the mixed conifer stands in the southern Rocky Mountains where Douglas-fir is associated with ponderosa pine, southwestern white pine (Pinus strobiformis), corkbark fir (Abies lasiocarpa var. arizonica), white fir (Abies concolor), blue spruce (Picea pungens), Engelmann spruce, and aspen (Populus spp.).

The most important shrubs associated with coastal Douglas-fir (21) through its central and northern range are vine maple (Acer circinatum), salal (Gaultheria shallon), Pacific rhododendron (Rhododendron macrophyllum), Oregongrape (Berberis nervosa), red huckleberry (Vaccinium parvifolium), and salmonberry (Rubus spectabilis). Toward the drier southern end of its range, common shrub associates are California hazel (Corylus cornuta var. californica), oceanspray (Holodiscus discolor), creeping snowberry (Symphoricarpos mollis), western poison-oak (Toxicodendron diversilobum), ceanothus (Ceanothus spp.), and manzanita (Arctostaphylos spp. ).

Principal understory species associated with variety glauca differ within its range (3). In the northern part, they are common snowberry (Symphoricarpos albus), white spirea (Spirea betulifolia), ninebark (Physocarpus malvaceus), and pachistima (Pachistima myrsinites). In the central part, they are true mountain-mahogany (Cercocarpus montanus), squaw currant (Ribes cereum), chokeberry (Prunus virginiana), big sagebrush (Artemisia tridentata), western serviceberry (Amelanchier alnifolia), and bush rockspirea (Holodiscus dumosus) in the southern part they are New Mexico locust (Robinia neomexicana), Rocky Mountain maple (Acer glabrum), and oceanspray (3).

Life History

Reproduction and Early Growth

Flowering and Fruiting- Douglas-fir is monoecious trees commonly begin to produce strobili at 12 to 15 years of age, although observations of younger seedlings bearing ovulate strobili have been reported.

Primordia of both pollen and seed cone buds are present when the vegetative bud breaks in the spring of the year before the cone crop. But neither can be distinguished from primordia of vegetative buds for the first 10 weeks of their existence. By mid-June, histochemical differences separate the pollen cone primordia, which are usually clustered near the base of the extending shoot, from the seed cone primordia, which are borne singly near the acropetal end of the shoot, and from the vegetative bud primordia (5). These three primordia may be microscopically identified in mid-July by September, the egg-shaped pollen cone buds are easily distinguished by the naked eye from the darker vegetative buds and the larger seed cone buds.

The size of the cone crop is determined by the number of primordia that differentiate and develop into buds, not by the number formed. Poor cone crops, then, reflect a high abortion rate of primordia the preceding year. Large numbers of pollen or seed cone buds in the fall merely indicate the potential for a heavy cone crop the following year. Damaging frost during cone anthesis or depredations by insects may destroy most of the cones and seeds before they mature (19).

Male strobili are about 2 cm (0.8 in) long and range from yellow to deep red. Female strobili are about 3 cm (1.2 in) long and range from deep green to deep red (45). They have large trident bracts and are receptive to pollination soon after emergence.

Anthesis and pollination of variety menziesii occur during March and April in the warmer part of the range and as late as May or early June in the colder areas. At low and middle elevations, Douglas-fir cones mature and seeds ripen from mid-August in southern Oregon to mid-September in northern Washington and southern British Columbia. Mature cones are 8 to 10 cm (3 to 4 in) long. The bracts turn brown when seeds are mature (45). Seedfall occurs soon after cone maturity with, generally, two-thirds of the total crop on the ground by the end of October. The remaining seeds fall during winter and spring months. In British Columbia, seedfall starts later and lasts longer-less than half the seeds fall by late October and more than one-third fall after March 1. In general, Douglas-fir seedfall in the fog belt of western North America is more protracted than in the drier areas east of the summit of the Coast Ranges.

The phenology of flowering is similar for variety glauca early flowering occurs in mid-April to early May in Colorado and as late as early May to late June in northern Idaho. Cone ripening varies from late July at the lower elevations (about 850 m or 2,800 ft) in Montana to mid-August in northern Idaho. Seed dispersal of glauca begins in mid-August in central Oregon and occurs as late as mid-September at higher elevations (about 1710 m or 5,600 ft) in Montana (45).

Seed quality varies during the seedfall period. It is high in the fall but declines rapidly during winter and spring. This pattern probably reflects the fact that cone scales in the center of the cone, where the highest quality seed are borne, open early and scales at the tip and base of the cone, which bear generally poorly formed seeds, open late.

Both cones and seeds vary greatly in size the smaller seeds (about 132,000/kg or 60,000/lb) occur on trees in British Columbia and the larger seeds (about 51,000/kg or 23,000/lb), on trees in California. Seeds of variety glauca are slightly heavier and more triangular in shape than seeds of menziesii. Size is determined before fertilization, so there is no correlation between weight of seed and genetic vigor, although seedlings germinated from heavier seeds may be slightly larger the first few months of growth than those grown from lighter seeds. Because the range in seed size from any one tree is relatively small, however, fractionation of seed lots to segregate the heavier seed may reduce the genetic variation and actually eliminate traits from certain populations.

Douglas-fir seed crops occur at irregular intervals- one heavy and one medium crop every 7 years on the average however, even during heavy seed years, only about 25 percent of the trees produce an appreciable number of cones (34). Trees 200 to 300 years old produce the greatest number of cones. For example, a stand of old-growth Douglas-fir may produce 20 to 30 times the number of cones per hectare that a second-growth stand 50 to 100 years old produces.

Seed Production and Dissemination- Major deterrents to natural regeneration of Douglas-fir include limited seed supply consumption of seed by insects, animals, and birds competing plant species and unfavorable environments. Although reports of fully stocked stands resulting from seedfall from sources 1 to 2 km (0.6 to 1.2 mi) distant are not rare, the great majority of Douglas-fir seeds fall within 100 m (330 ft) of a seed tree or stand edge (18).

Data describing the quantities of seeds that may fall vary widely, but most years are characterized by less than 2.2 kg/ha (2 lb/acre), of which no more than 40 percent is sound. Years with poor seed crops generally have a lower percentage of viable seeds, perhaps because the low incidence of fruiting trees may favor a higher level of selfing (25).

Seedling Development- Douglas-fir germination is epigeal. Seed germinates in mid-March to early April in the warmer portions of the range and as late as mid-May in the cooler areas. Seedling growth the first year is indeterminate but relatively slow and limited generally by moisture, which triggers initiation of dormancy in midsummer. The dormant period normally extends from midsummer until April or May of the following year (37). Douglas-fir can produce lammas shoots, but this habit is confined to either the more moist portion of the range or to years with abnormally heavy summer rainfall. This habit is probably most pronounced in the southern Rockies, where the summer period is characterized by irregular, heavy rainstorms. In any event, the great majority of the annual shoot growth occurs during the initial flush. First-year seedlings on better sites in the Pacific Northwest may develop shoots 6 to 9 cm (2.5 to 3.5 in) long. Growth in subsequent years is determinate and gradually accelerates so that when saplings are 8 to 10 years old, terminal growth may consistently exceed 1 m (3.3 ft) per year on the more productive sites.

Seedlings of the variety menziesii normally survive best when the seed germinates on moist mineral soil, but menziesii will tolerate a light litter layer. Seedlings do not survive well, however, on heavy accumulations of organic debris. In contrast, seedlings of the variety glauca are favored by a duff layer, especially in the larch forests of northwestern Montana (53).

First-year seedlings survive and grow best under light shade, especially on southerly exposures, but older seedlings require full sunlight. Particularly in the fog belt, competing vegetation such as alder, maple, salmonberry, and thimbleberry (Rubus parviflorus) limits Douglas-fir regeneration by creating intolerable levels of shade plants such as grasses, manzanita, ceanothus, and oak compete strongly for available moisture and plants such as bracken (Pteridium aquilinum) and vetch (Vicia spp. ) smother small seedlings with leaves and other debris. Successful regeneration of variety menziesii often depends on weed control in the commercial range of Douglas-fir because many associated plant species have growth rates much greater than that of juvenile Douglas-fir (8). For this reason, regeneration may be more reliable after a wildfire, which destroys the reservoir of potential competitive species, than after a harvest operation, which leaves areas well suited to the rapid proliferation of the herbaceous and woody competitors of Douglas-fir.

In the Rocky Mountains, competing vegetation may promote the establishment of variety glauca seedlings by reducing temperature stress and may inhibit seedling growth by competing strongly for moisture. The latter effect is most pronounced in the southern portions of glauca's range.

Microsites with adverse moisture and temperature conditions frequently limit establishment of both menziesii and glauca seedlings on southerly aspects (32). Soil surface temperatures in excess of 65° C (149° F) are prevalent in the southern Cascade Range and Siskiyou Mountains and are common in the Cascades even as far north as Mount Rainier. Prolonged droughts, which may extend from May through September, are frequent in southern Oregon and northern California, and low annual precipitation and high evaporation stress greatly limit the distribution of glauca in the Rocky Mountains.

Like nearly all perennial woody plants, Douglas-fir is dependent on a mycorrhizal relationship for efficient uptake of mineral nutrients and water. Approximately 2,000 species of fungi have been identified as potential symbionts with Douglas-fir, and both ectomycorrhizal and ectendomycorrhizal structures have been observed on this species (59). Occasionally, nursery practices result in seedlings with few mycorrhizae, but no deficiencies in mycorrhizal infection have been reported for natural seedlings.

Historically, large burned or cleared areas in the range of variety menziesii, such as those on Vancouver Island (52), have naturally seeded into nearly pure stands of Douglas-fir. On mesic to moist sites this process may occur over a relatively short period, perhaps 10 to 15 years. On drier sites, such regeneration may be quite protracted and require a hundred or more years. Stocking of harvested areas has been extremely variable during the past 30 years, and large tracts in the drier or cooler portions of the range are covered by brush species such as manzanita, ceanothus, salmonberry, salal, or lower value hardwoods, such as alder, maple, and oak.

Regeneration of variety glauca in the Rocky Mountains has also been variable. In general, glauca may be considered a seral species in moist habitats and a climax component in the warmer, drier areas. Regeneration is favored where Douglas-fir is seral, especially in northern Idaho and western Montana where a strong maritime influence modifies the generally continental climate that prevails in the central and southerly Rocky Mountains. In contrast, regeneration of Douglas-fir is poor where the species has attained climax status (49).

From 1950 until about 1970, large areas of cutover and burned-over forest land in the Pacific Northwest were aerially seeded. Direct seeding suffers from the same deficiencies as natural regeneration, however that is, stands produced are often uneven in stocking and require interplanting or pre-commercial thinning, and animals destroy a large proportion of the seeds. With the advent of greatly increased forest nursery capacity, direct seeding is much less common (13,54).

Vegetative Reproduction- Douglas-fir does not naturally reproduce vegetatively. Substantial research to develop cuttings as a regeneration procedure has demonstrated that reliable rooting of cuttings is limited to material collected from trees less than 10 years old, or from trees that have been subjected to repeated shearing to regenerate material with a juvenile habit. A second major impediment to the use of cuttings as a regeneration technique for this species is that most such material has a period of plagiotropic growth, which may be lengthy, before the erect habit is assumed.

Research with tissue culture techniques has demonstrated substantial promise, but widespread use of this technique in reforestation of the Douglas-fir region is, at best, a future possibility.

Sapling and Pole Stages to Maturity

Growth and Yield- Natural stands of coastal Douglas-fir normally start with more than 2,500 trees per hectare (1,000/acre). Planted stands generally have between 750 and 1,500/ha (300 and 600/acre) at the beginning (9). Annual height increment is relatively slow the first 5 years but then begins to accelerate. Coastal Douglas-fir attains the largest height increments between 20 and 30 years of age but retains the ability to maintain a fairly rapid rate of height growth over a long period. Douglas-fir in high-elevation forests of the Oregon-Washington Cascade Range can continue height growth at a substantial rate for more than 200 years (15). Height growth of Douglas-fir on dry sites at mid-site indices in the Cascade Range of western Oregon is similar to that of upper-slope Douglas-fir in the Washington and Oregon Cascade Range. At higher site indices, however, height growth on dry sites is initially faster but slower later in life at lower site indices, it is initially slower but faster later in life (40).

On a medium site (III) at low elevations, height growth, which averages 61 cm (24 in) annually at age 30, continues at a rate of 15 cm (6 in) per year at age 100, and 9 cm (3.6 in) at age 120 (18,39). Trees 150 to 180 cm (60 to 72 in) in diameter and 76 m (250 ft) in height are common in old-growth forests (22). The tallest tree on record, found near Little Rock, WA, was 100.5 m (330 ft) tall and had a diameter of 182 cm (71.6 in). Coastal Douglas-fir is very long lived ages in excess of 500 years are not uncommon and some have exceeded 1,000 years. The oldest Douglas-fir of which there is an authentic record stood about 48 km (30 mi) east of Mount Vernon, WA. It was slightly more than 1,400 years old when cut (39).

Information about yields of coastal Douglas-fir under intensive management for an entire rotation is still limited. It is therefore necessary to rely either on estimates based on yields from unmanaged stands, or on yields from intensively managed stands in regions where Douglas-fir has been introduced as an exotic (12), or on growth models (16). If measured in cubic volume of wood produced, range in productivity between the best and poorest sites is more than 250 percent. Depending on site quality, mean annual net increments at age 50 vary from 3.7 to 13.4 m³/ha (53 to 191 ft³/acre) in unmanaged stands (39). Estimates of gross yields may increase these values as much as 80 percent, depending on mensurational techniques and assumptions. Comparisons of gross yields from unmanaged stands with those from managed stands of the same site indexes in Europe and New Zealand suggest that yields in managed stands will be considerably higher than would be indicated by estimates based on yields in unmanaged stands. Presumably, managed stands of coastal Douglas-fir can produce mean annual increments of 7 m³/ha (100 ft³/acre) on poor sites and exceed 28 m³/ha (400 ft³/acre) on the highest sites under rotations between 50 and 80 years (55). Although information on productivity of Douglas-fir in terms of total biomass production is still limited, indications are that it may reach 1000 t/ha (447 tons/acre) on high sites (22).

The interior variety of Douglas-fir does not attain the growth rates, dimensions, or age of the coastal variety. Site class for Rocky Mountain Douglas-fir is usually IV or V (site index 24 to 37 m or 80 to 120 ft at age 100) when compared with the growth of this species in the Pacific Northwest (1,43). On low sites, growth is sometimes so slow that trees do not reach saw-log size before old age and decadence overtake them. Interior Douglas-fir reaches an average height of 30 to 37 m (100 to 120 ft) with a d.b.h. between 38 and 102 cm (15 and 40 in) in 200 to 300 years. On the best sites, dominant trees may attain a height of 49 m (160 ft) and a d.b.h. of 152 cm (60 in) (23). Diameter growth becomes extremely slow and height growth practically ceases after age 200. Interior Douglas-fir, however, appears capable of response to release by accelerated diameter growth at any size or age (35). The interior variety is not as long lived as the coastal variety and rarely lives more than 400 years, although more than 700 annual rings have been counted on stumps (23).

Gross volume yields for Douglas-fir east of the Cascades in Oregon and Washington range from 311 m³/ha (4,442 ft³/acre) for site index 15.2 m or 50 ft (at age 50) to 1523 m³/ha (21,759 ft³/acre) for site index 33.5 m (110 ft) (14). In the northern Rocky Mountains, estimates of yield capabilities of habitat types where Douglas-fir is climax range from about 1.4 to 7 m³/ha (20 to 100 ft³/acre) per year to more than 9.8 m³/ha (140 ft³/acre) per year in some of the more moist habitat types where Douglas-fir is seral (46).

Information on yields of Douglas-fir in the southern Rocky Mountain region is scant. In New Mexico, a virgin stand of Douglas-fir (61 percent) and associated species averaged 182 m³/ha (13,000 fbm/acre). Occasionally, stands yield as high as 840 m³/ha (60,000 fbm/acre). Annual growth rates from 2.0 to 3.9 m³/ha (140 to 280 fbm/acre) after partial cutting have been reported in New Mexico (17).

Rooting Habit- Although Douglas-fir is potentially a deep-rooting species, its root morphology varies according to the nature of the soil. In the absence of obstructions, Douglas-fir initially forms a tap root that grows rapidly during the first few years. In deep soils (69 to 135 cm, 27 to 53 in), it was found that tap roots grew to about 50 percent of their final depth in 3 to 5 years, and to 90 percent in 6 to 8 years however, boulders or bedrock close to the soil surface result in quick proliferation of the original tap root. Platelike root systems develop when Douglas-fir grows in shallow soils or soils with a high water table. Main lateral branches develop during the first or second growing season as branches of the tap root. These structural roots tend to grow obliquely into deeper soil layers and contribute to anchoring a tree. The majority of roots in the surface soil are long rope-like laterals of secondary and tertiary origin. Fine roots, those less than 0.5 cm (0.2 in) in diameter, develop mostly from smaller lateral roots and are concentrated in the upper 20 cm (8 in) of soil (29). Fine roots have a short life-span, ranging in general from a few days to several weeks. Cyclic death and replacement of fine roots changes seasonally, reflecting changes in environmental conditions (51).

Size of the root system appears to be related to size of the crown rather than the bole. In British Columbia, ratios of root spread to crown width averaged 1.1 for open- and 0.9 for forest-grown Douglas-fir, but greater lateral spread has been observed on poorly drained sand and sandy gravel soils. The radial symmetry of root systems seems to be readily distorted by slope, proximity to other trees, and presence of old roots. Observations in the Pacific Northwest and the Rocky Mountains indicate that roots of Douglas-fir extend farther downslope than upslope.

The proportion of root biomass decreases with age and may vary from 50 percent at age 21 to less than 20 percent in stands older than 100 years (29). Root grafting is very common in stands of Douglas-fir, often leading to a system of interconnected roots in older stands (36).

Reaction to Competition- Except in its youth, when it is reasonably tolerant of shade, coastal Douglas-fir is classed as intermediate in overall shade tolerance, below most of its common associates in tolerance to shade (42). Of these associates, ponderosa pine, Jeffrey pine (Pinus jeffreyi), incense-cedar, noble fir (Abies procera), and red alder are more demanding of light. In its interior range, Douglas-fir ranks intermediate in tolerance among its associates, being more tolerant than western larch, ponderosa pine, lodgepole pine, southwestern white pine, and aspen (23).

The coastal variety is a seral species, except on extremely dry sites in southwestern Oregon and northern California. In its interior range, Douglas-fir is both a climax and a seral species. In the northern Rocky Mountains, it replaces ponderosa pine, lodgepole pine, and western larch above the ponderosa pine belt, and in turn is replaced by western redcedar, western hemlock, Engelmann spruce, grand fir, and subalpine fir on cooler and wetter sites. In the southern Rocky Mountains, Douglas-fir is a climax species in several habitat types of mixed conifer forest and a seral species in the spruce-fir forests (4).

The natural occurrence of Douglas-fir in extensive stands is mainly a consequence of forest fires. The species' rapid growth and longevity, the thick corky bark of its lower boles and main roots, combined with its capacity to form adventitious roots, are the main adaptations that have enabled Douglas-fir to survive less fire-resistant associates and to remain a dominant element in western forests. Without fire or other drastic disturbance, Douglas-fir would gradually be replaced throughout much of its range by the more tolerant hemlock, cedar, and true fir. Old-growth forests of Douglas-fir tend to show wide ranges in age structure-rather than being even-aged- which indicates that Douglas-fir was not established over short periods after major fires or other disturbances (22).

Stands of vigorous Douglas-fir can be successfully regenerated by any of the even-aged methods. Clear cutting in combination with planting is the most widely used method. In stands infected with dwarf mistletoe (Arceuthobium spp. ), clearcutting is the best alternative for eliminating the disease. If clearcutting on good sites results in establishment of red alder, Douglas-fir is at a severe disadvantage. Alder has very rapid juvenile growth on high sites and can easily over top and suppress Douglas-fir. If Douglas-fir is released in time, however, its subsequent development will actually benefit from the nitrogen fixed by red alder. Nitrogen is the only nutrient in forest soils of the Pacific Northwest (41) and Intermountain Northwest (44) that has been shown to be limiting to growth of Douglas-fir.

Because of its ability to tolerate shade in the seedling stage, the shelterwood system is a feasible alternative to clearcutting in coastal stands (64). Shelterwood cutting has been practiced only on a limited scale in the Pacific Northwest, however, where the large dimensions of old-growth timber, danger of blowdown to the residual stand, and probability of brush encroachment limit its use. In the Rocky Mountains, shelterwood cutting has been more commonly applied and with good results (50). Where interior Douglas-fir is climax, the true selection method can be used. It is unsuitable for coastal Douglas-fir.

Although Douglas-fir may be regenerated either naturally or artificially from seed, the erratic spacing characteristic of many naturally regenerated stands and the general lack of reliability of this system have resulted in legislation (Forestry Practices Acts) in Washington, Oregon, and California that virtually mandates artificial regeneration. And, because direct seeding also produces variable results, the regeneration system uses 2-year-old bare root seedlings, 3-year-old transplants, year-old container-grown seedlings, or 2-year-old transplants that were grown the first year in containers (9). Such planting stock may be affected by agents discussed here under the heading "Damaging Agents" or may suffer mortality from a lack of vigor occasioned by improper production and harvest practices, from poor planting practices, and from frost damage incurred either in nursery beds or after planting (13).

When Douglas-fir develops in a closed stand, the lower limbs die rapidly as they are increasingly subjected to overhead shade. Nevertheless, natural pruning is exceedingly slow because even small dead limbs resist decay and persist for a very long period. On the average, Douglas-fir is not clear to a height of 5 m (17 ft) until 77 years old, and to 10 m (33 ft) until 107 years. Obviously, natural pruning will not produce clear butt logs in rotations of less than 150 years. Artificial pruning will greatly reduce the time required to produce clear lumber but may result in severe grain distortion and brittle grain structure around pruning wounds (10).

Seedlings and saplings of Douglas-fir respond satisfactorily to release from competing brush or overstory trees if they have not been suppressed too severely or too long. Trees of pole and small sawtimber size in general respond very well to thinning. Trees that have developed in a closed stand, however, are poorly adapted to radical release, such as that occasioned by very heavy thinning. When exposed, the long slender holes with short crowns are highly susceptible to damage from snowbreak, windfall, and sunscald. Sudden and drastic release of young Douglas-fir may cause a sharp temporary reduction in height growth (57). Application of a nitrogen fertilizer in combination with thinning gives better growth responses in Douglas-fir than either fertilizer or thinning alone (41).

Damaging Agents- From seed to maturity, Douglas-fir is subject to serious damage from a variety of agents. Douglas-fir is host to hundreds of fungi, but relatively few of these cause serious problems. Various species of Pythium, Rhizoctonia, Phytophthora, Fusarium, and Botrytis may cause significant losses of seedlings in nurseries (58,60), whereas Rhizina undulata, shoestring root rot (Armillaria mellea), and laminated root rot (Phellinus weirii) have caused significant damage in plantations. In fact, the latter two fungi represent a serious threat to management of young-growth stands of Douglas-fir, especially west of the summit of the Cascades. Trees die or are so weakened that they are blown over. Effective control measures are not available. Of the many heart rot fungi (more than 300) attacking Douglas-fir, the most damaging and widespread is red ring rot (Phellinus pini). Knots and scars resulting from fire, lightning, and falling trees are the main courts of infection. Losses from this heart rot far exceed those from any other decay. Other important heart rot fungi in the Pacific Northwest are Fomitopsis officinalis, F. cajanderi, and Phaeolus schweinitzii (28). In the Southwest, Echinodontium tinctorium, Fomitopsis cajanderi, and F. pinicola are important.

Several needle diseases occur on Douglas-fir. The most conspicuous, a needlecast, is caused by Rhabdocline pseudotsugae. It is mainly a disease of younger trees, reaching damaging proportions only after prolonged periods of rain while the new needles are appearing. The interior variety is particularly susceptible to the disease but is less often exposed to long periods of rain during the spring growth period.

The most damaging stem disease of Douglas-fir is Arceuthobium douglasii. This dwarf mistletoe occurs throughout most of the range of Douglas-fir (26).

Over 60 species of insects are indigenous to Douglas-fir cones, but only a few species damage a significant proportion of the seed crop. Damage by insects is frequently more pronounced during the years of light or medium seed crops that may follow good or heavy crops.

The most destructive insects include: (a) the Douglas-fir seed chalcid (Megastigmus spermotrophus), which matures in the developing seed and gives no external sign of its presence (b) the Douglas-fir cone moth (Barbara colfaxiana) and the fir cone worm (Dioryctria abietivorella) whose larvae bore indiscriminately through the developing cones and may leave external particles of frass and (c) the Douglas-fir cone gall midge (Contarinia oregonensis) and cone scale midge (C. washingtonensis), which destroy some seed but prevent harvest of many more by causing galls that prevent normal opening of cones. The Douglas-fir cone moth is perhaps a more serious pest in the drier, interior portions of the Douglas-fir range and the Contarinia spp. in the wetter regions. Any of these insects, however, may effectively destroy a cone crop in a given location (27).

Insects are generally not a severe problem for Douglas-fir regeneration, although both the strawberry root weevil (Otiorhynchus oratus) and cranberry girdler (Chrysoteuchia topiaria) may cause significant damage to seedlings in nurseries damage to plantations by rain beetles (Pleocoma spp.) and weevils (Steremnius carinatus) - the latter particularly damaging to container-grown-plants-has been reported.

The Douglas-fir tussock moth (Orgyia pseudotsugata) and the western spruce budworm (Choristoneura fumiferana) are the most important insect enemies of Douglas-fir. Both insects attack trees of all ages at periodic intervals throughout the range of interior Douglas-fir, often resulting in severe defoliation of stands. The Douglas-fir beetle (Dendroctonus pseudotsugae) is a destructive insect pest in old-growth stands of coastal and interior Douglas-fir. Its impact is diminishing, however, with the change to second-growth management and rotations of less than 100 years (24).

Consumption of Douglas-fir seeds by small forest mammals such as white-footed deer mice, creeping voles, chipmunks, and shrews, and birds such as juncos, varied thrush, blue and ruffed grouse, and song sparrows further reduces seed quantity. A single deer mouse may devour 350 Douglas-fir seeds in a single night. Mouse populations of 7 to 12/ha (3 to 5/acre) are not uncommon. Most seedfall occurs at least 150 days before the germination period, so this single rodent species has the capacity to destroy the great majority of natural seedfall. Spot seeding studies in the Western United States have clearly demonstrated that forest mammals destroy virtually all unprotected seed.

Browsing and clipping by hares, brush rabbits, mountain beaver, pocket gophers, deer, and elk often injure seedlings and saplings. Recent reports have indicated that such damage in western Oregon and Washington may strongly affect seedling survival in many plantations (7,61). In drier areas, domestic livestock have caused considerable damage to variety glauca plantations by grazing and trampling seedlings. In pole-sized timber, bears sometimes deform and even kill young trees by stripping off the bark and cambium.

High winds following heavy rains occasionally cause heavy losses from blowdown in the Pacific Northwest. Heavy snow and ice storms periodically break the tops of scattered trees in dense young stands. Crown fires, when they occur, destroy stands of all ages. The thick bark of older Douglas-firs, however, makes them fairly resistant to ground fires.

Special Uses

Douglas-fir is grown as a Christmas tree on rotations ranging from 4 to 7 years. Trees are sheared each year to obtain a pyramid-shaped crown. Attempts to grow Douglas-fir as a Christmas tree in North America outside its native range have failed. Coastal Douglas-fir is usually killed by frost, and the interior variety suffers too much from the needle cast disease Phaeocryptopus gaeumanni.

Genetics

The genus Pseudotsuga includes two species (P. menziesii and P. macrocarpa) indigenous to North America and five species native to Asia. All except P. menziesii have a karyotype of 2N=24, the number of chromosomes characteristic of Pinaceae. But the Douglas-fir karyotype is 2N=26, a probable reason for the general failure of hybridization trials with this species (56).

Population Differences

Pseudotsuga menziesii has two widely recognized varieties: menziesii, the green variety indigenous to the area west of the summit of the Cascade Range in Washington and Oregon and of the Sierra Nevada in California and glauca, the blue Douglas-fir native to the interior mountains of the Pacific Northwest and the Rocky Mountains in the United States, and to Mexico. The division between the two varieties is not as clearly defined in Canada, although menziesii is commonly considered indigenous to the area west of the crest of the mainland Coast and Cascade Ranges.

The varieties differ in both growth rate and size at maturity, menziesii being more rapid growing and much larger. In habit, glauca is more shade tolerant, has a more pronounced tap root, is more susceptible to Rhabdocline pseudotsugae when grown in a moist environment, and is significantly more cold hardy. The coastal and interior varieties also differ in botanical and morphological characteristics. Because of variation within the two recognized varieties, it has been suggested that variety glauca be replaced with several varieties, and many forms have been reported. Chemical and cytological investigations have shown differences both between and within the two varieties, but such work has not led to further differentiation (38,48).

Races

Douglas-fir has one of the broadest ranges of any North American conifer, much of it over extremely dissected terrain, and the species exhibits a great deal of genetic differentiation. Much of this variation is strongly associated with geographic or topographic features (47). Thus, clinal patterns of variation in growth and pherrological traits have been observed over north-south, east-west, and elevational transects despite the appreciable gene flow expected in this species. Adaptive patterns of genetic variation also occur among Douglas-fir populations within local regions. For example, evidence exists for "aspect races" in variety menziesii: Seedlings grown from seed collected on the more xeric southern aspects grow slower, set buds earlier, and form larger roots in relation to shoots than seedlings grown from seeds collected on adjacent north-facing slopes. Seedlings from seed sources on the south aspect have characteristics consistent with adaptation to the shorter growing seasons and drier soil conditions generally found on south-facing slopes and may be better able to survive under drought stress than seedlings from north-aspect seed sources (33). Topoclinal variation in response to microenvironmental heterogeneity has also been found in the central part of the Oregon Cascades (11).


Using a novel assessment framework to evaluate protective functions and timber production in Austrian mountain forests under climate change

In Central European mountain forests, timber production and the protection of infrastructure and settlements against gravitational natural hazards are key forest ecosystem services (ES). The quantitative assessment of mountain forest ES for management planning and decision support is a particular challenge, due to manifold involved spatial scales from tree to slope and landscape level. We present an assessment framework to analyze and communicate the effect of management and climate change on the provision of selected ES in mountain forests. Core element is the spatially explicit hybrid forest ecosystem model PICUS. Remote sensing data and inventories are combined to generate realistic fine-grained forest landscapes with single tree resolution as input to PICUS. Landscape-level planning of silvicultural prescriptions employs geographic information systems functionalities (locate skyline corridors and treatment areas, prescribe silvicultural operations based on tree-level attributes) and produces management maps, which are interpreted by PICUS and executed in course of simulation runs. Model output is imported into a spatially explicit landscape assessment tool to assess the protective effect of vegetation. In a 250 ha case study in the Eastern Alps in Austria, the assessment framework is demonstrated to evaluate effects of climate change and management on timber production and protection against landslides and snow avalanche release. Climate change had, depending on climate and management scenario both, positive and negative impacts on desired ES. Key factor for ES provisioning in the case study was the interaction of bark beetle disturbances, legacies of past land-use practices and forest management.

This is a preview of subscription content, access via your institution.