Ecology of the North Cascades
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The Ecology of the North Cascades is heavily influenced by the high elevation and rain shadow effects of the mountain range. The North Cascades is a section of the Cascade Range from the South Fork of the Snoqualmie River in Washington, United States, to the confluence of the Thompson and Fraser Rivers in British Columbia, Canada, where the range is officially called the Cascade Mountains but is usually referred to as the Canadian Cascades. The North Cascades Ecoregion is a Level III ecoregion in the Commission for Environmental Cooperation's classification system.[1]
The terrain of the North Cascades is composed of high, rugged mountains. It contains the greatest concentration of active alpine
The North Cascades has a diversity of plant and animal species.
The ecology of the area can be understood by following a west-to-east line at the southern end of the North Cascades, at approximately 47.5 degrees north. As the line passes through the Cascade range, it passes through a number of ecoregions, first getting higher and colder, then getting warmer, yet drier. Each of these component ecoregions can be described by either a tree
Western Hemlock Ecoregion
The Western Hemlock Ecoregion huddles in the lower west-side elevations of the North Cascades. Western hemlock is found from sea level up to 2,500 feet (800 m) in elevation.
Silver Fir Ecoregion
The mid-elevation forests in the North Cascades with an elevation between 2,000 and 4,300 feet (600 and 1,300 m) is the Silver Fir Ecoregion.
The Pacific silver fir (Abies amabilis) is extremely tolerant of shade and does not fare as well in drought or warmer temperatures.
Subalpine Mountain Hemlock Ecoregion
Moving up in elevation from the Silver Fir Ecoregion, between about 4,000 and 5,400 feet (1,200 and 1,600 m) on the west side of the Cascade Range, the ecoregion shifts to the Subalpine Mountain Hemlock Ecoregion.
Progressing upward from the gradient of Silver Fir and Mountain Hemlock ecoregions, the mountain hemlock (Tsuga mertensiana) tends to become the dominant conifer, although it may codominate with the Alaska cedar and Pacific silver fir. Mountain hemlock trees live as long as 1000 years: longer than the Pacific silver fir. Trees between 500 and 700 years may be 100 to 125 feet (30 to 40 m) tall.[6] Hemlock cones are about 2–3 inches (5–8 cm) in length and develop at the ends of branches.[6] These conifers are easy to distinguish amongst the others with their dense grayish-green needles.[6] According to Franklin and Dyrness, the understory where the mountain hemlock and Pacific silver fir co-dominate is dominated by tall mountain huckleberry; where the Alaska cedar dominates, the understory is dominated by dense collage of rhododendron, huckleberry and mountain ash.[6]
In the higher boundaries of subalpine ecosystem, where the abiotic conditions are more stressful, trees are clumped together in patchy islands. Trees in this area can be recognized by its krummholz form. Trees of this upper boundary will take on a flag appearance with branches extending from one side indicating the prevailing wind directions. The skirt height of the trees is indicative of the height of snow cover where branches tend not to grow.[6] There are various reasons as to why these trees take this form. Strong winds combined with ice particles will cause abrasion scouring the waxy cuticle from one side of the tree creating damage that will prevent branch formation and growth.[6] In addition, the wind will cause desiccation and evaporation in the needles causing branches to die on this side of the trees.
Scattered amongst the island patches of trees in the upper boundaries are parkland areas with showy meadows. Events such as fire, avalanches, snow slumping and climate change make the boundaries of these areas and the balance of trees and meadows dynamic. Invasions of meadows by trees can also occur with disturbances.
The beauty of meadows is very popular amongst hikers. Wildflowers that are found in this ecoregion are the
The two dominant vegetation types of this mountain region, forests and meadows, have very distinct differences in their microclimates. The amount of solar radiation and UV exposure can vary substantially in our northern latitude largely based on the time of day, slope, season, cloud cover and vegetation.[6] Temperatures adjust accordingly to this solar radiation and exposure. The parklands of this montane region have a much larger range of temperatures as compared to the hemlock forests.[6] The range can be as much as 50 °F (28 °C) while the range in the forests rarely exceeds 20 °F (11 °C).[6] This is due to the canopy of the trees, creating a much more protected environment as compared to the open meadows. In addition soil temperatures directly impact biological activity affecting soil organisms and root systems.[6] Daily and season temperature changes greatly affect the soils' heat loss and gain.[6] However, the snowpack acts as an insulating buffer against temperature change in soils.[6] The mountain hemlock forests are the wettest and coldest of the Cascade forest zones.[6]
In the richness of this region many animal species pass through this zone at least one season a year such as mountain goat, black-tailed deer, American black bear, elk, cougar, and many bird species.[6] Only the whistling hoary marmot is restricted to alpine and subalpine areas.[6] Besides the richness of mammals there is a richness of insects that are integral to the abundance of flowering plant species in this area.[6] Another important pollinator in this area is the hummingbird.[6] There is still much to be researched and discovered to better understand species interactions and reliance in both the alpine and subalpine ecosystems.
Alpine Ecoregion
The Alpine Ecoregion makes up much of the North Cascades. Alpine areas such as this are rugged with rocky ridges,
This high elevation habitat of high winds, prolonged snow cover, steep terrain, high temperature variability, and intense UV radiation lead to special species adaptations.[10] Alpine regions generally have hypoxic conditions that lead to additional energy expenses for organisms.[10] Increased elevations usually lead to shorter breeding season in animals, as is the case in the alpine ecosystems in the North Cascades. In addition to the shorter breeding season, wildlife often requires seasonal movement to different elevations in order to find adequate food and habitat.[10] However, species such as the white-tailed ptarmigan, hoary marmots, and pikas remain in high elevations of the Cascades year round left only to go to patchy and scattered alpine vegetation. The majority of species will move to lower elevations at some time throughout their life history. Adaptations such as torpor in hummingbirds, the ability of mountain goats and coyotes to camouflage in the landscape, animals developing extra fat deposits, and the raptor's ability to move efficiently in the strong winds illustrate just some of the ways species have been ability to cope with alpine conditions.[10] The white-tailed ptarmigan has an adaption of changing its plumage from white in the winter to brown in the summer in order to camouflage.[10] Many species in higher elevations produce fewer offspring than in lower elevations but spend more time nurturing their young.[10]
While alpine ecosystems provide challenging abiotic conditions for species there are advantages to animal species to habituate these areas. In the winter while there is extensive snow pack there are also strong winds that will expose herbaceous stems and seeds for animals to forage on.[10] Insects that are blown up from lower elevations will land on the snow beds in the spring offering much nutrition for birds and other mammals that breed in the alpine.[10] When snowfields melt it creates a gradient of plant phenology which provides emerging vegetation over a period of time for herbivores to feed on and migrate along this line. Spring foraging is believed to be crucial in the breeding in a number of species such as the mountain goat.[10] Leaf budding and fruiting in late summer past the edges of snowfields also offer food for the animals that depend on this area.[10] Black bears, songbirds and marmots in the North Cascades and Alpine Lakes can find cover in lush vegetation in avalanche chutes adjacent to the subalpine forests.[10] There seems to also be evidence that there is a lower rate of parasitism and disease in these high alpine elevations offering yet another advantage to alpine species. The alpine grouse is one example of an alpine animal that has few blood infections or intestinal parasites.[10] Other animal species in the summer months will migrate into the higher alpine elevations to avoid insects and forage in the meadows.[10]
Subalpine Fir Ecoregion
The Subalpine Fir Ecoregion, descending down the east-side of the Cascade Range, reaches elevations between 4,200 and 6,000 feet (1,300 and 1,800 m).
The subalpine fir forests in the North Cascades include
Grand Fir/Douglas Fir Ecoregion
Descending down the east side of the Cascade Range is the
In the upper regions of this ecoregion, the dominant conifers are the mountain hemlock and subalpine fir and in the lower boundary the
Fauna
A variety of
Over 75 species of mammals occur in the range, including the mountain goat that lives in the high alpine tundra.[3] Bird species include the bald eagle, osprey, and harlequin duck.[14] Examples of amphibians occurring in the North Cascades include the western toad, Bufo boreas, and the rough-skinned newt, Taricha granulosa.[5] An unusual feature of the rough-skinned newt populations is that approximately ninety percent of the adult population is perennibranchiate.[15]
See also
- Alpine Lakes Wilderness
- Glacier Peak Wilderness
- Henry M. Jackson Wilderness
- North Cascades National Park
- Ecozones of Canada
- Biogeoclimatic zones of British Columbia
References
- ^ "Ecological Regions of North America, Level I-III" (PDF). Commission for Environmental Cooperation. Retrieved April 6, 2009.
- ^ "Level III ecoregions" (PDF). Western Ecology Division. U.S. Environmental Protection Agency. Retrieved March 11, 2009.
- ^ a b c d e Kefauver, Karen (September 15, 2010). "North Cascades National Park: Wildlife". GORP. Orbitz. Archived from the original on April 27, 2012. Retrieved June 6, 2012.
- ^ "Plants". North Cascades National Park. National Park Service. May 16, 2012. Retrieved June 6, 2012.
- ^ a b Rawhouser, Ashley K.; Holmes, Ronald E.; Glesne, Reed S. (2009). "A Survey of Stream Amphibian Species Composition and Distribution in the North Cascades National Park Service Complex, Washington State" (PDF). Archived from the original (PDF) on October 16, 2011. Retrieved June 7, 2012.
- ^ ISBN 0-295-97477-X.
- ^ a b c d e f g h i Alpine Lakes Area Land Management Plan (Report). USDA Forest Service. 1981.
- ^ a b c d e f g h i j k l m Gold, W. (January 28, 2008). "BIS258 lecture notes" (PDF). University of Washington. Retrieved March 15, 2009.
- ^ a b "Pacific Silver Fir" (PDF). Washington Department of Natural Resources. Archived from the original (PDF) on May 23, 2011. Retrieved March 11, 2009.
- ^ ISBN 0-87071-488-0.
- ^ ISBN 0-7627-3098-6.
- ^ "Grizzly Bears In the USA and the North Cascades: Past and Present". Grizzly Bear Outreach Project. Archived from the original on January 8, 2008. Retrieved August 24, 2009.
- ^ "Gray Wolf Conservation and Management". Washington Department of Fish & Wildlife. Retrieved May 8, 2011.
- ^ a b "Animals". North Cascades National Park. National Park Service. Retrieved June 6, 2012.
- ^ Hogan, C. Michael (2008). Nicklas Stromberg (ed.). "Rough-skinned Newt (Taricha granulosa)". Globaltwitcher. Archived from the original on May 27, 2009. Retrieved May 21, 2009.