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Wildlife of Eastside Shrubland and Grassland Habitats PDF Format - [6.9MB]
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Wildlife of Eastside Shrubland and Introduction The rain shadow of the Cascade Mountains gives rise to a suite of and and semi-arid habitats that differ substantially from those of the surrounding forest. O'Neil and Johnson100 have classified these habitats into 6 different types: shrub-steppe, dwarf shrubsteppe, desert playa and salt scrub, western juniper and mountain mahogany woodlands, eastside canyon shrublands, and eastside grasslands. Most of these communities are dominated by shrubs and herbaceous vegetation (grasses and forbs) and typically have a microbiotic crust of lichens and mosses binding the upper surface of the soil. With the exception of the western juniper and mountain mahogany woodlands habitat type, trees in these communities are limited mainly to riparian zones and ecotones with forested habitats and are entirely absent from extensive areas. Much of the historical vegetation in these habitat types, particularly in Washington and north central Oregon, has been converted to agricultural crops.27,113 In some areas, the only remaining native communities are on rocky soils or steep slopes unfit for agriculture. The dominant land use in these shrubland and grassland habitats is, livestock grazing, and few examples of undisturbed stands exist, limited primarily to sites where topography or remoteness from water has made access for livestock grazing impractical." Although pristine climax communities do exist for eastside grassland and shrubland habitats, the majority of sites have been shaped by a legacy of past land uses that includes continuous grazing by livestock and range improvements to increase livestock forage and that in turn has facilitated invasion by exotic vegetation. This legacy has modified the vegetation community in many areas, with some changes occurring so long ago that they are not apparent to the present day observer.22 Changes in the herb community brought about by excessive grazing and exotic invaders are particularly damaging in these and habitats where the herb layer often contains the most vegetation biomass. Moreover, the successional trajectory of vegetation communities in and habitats can be modified by influences such as grazing and fire, resulting in present day "zootic" climax communities that differ greatly from those which occurred historically.22,128 Sites in southcentral Washington that were dominated by exotic annuals in the 1950s still have not been colonized by native plants some four decades later.115 The low vertical structural diversity inherent in these habitats provides fewer habitat layers for wildlife, resulting in lower diversity in some taxa. There are, for example, no arboreal mammals or canopy nesting birds. Habitats with a shrub component tend to have more diverse wildlife communities than grass dominated habitats, a function of increased nesting and foraging strata. For example, the shrubsteppe habitat has 49 closely associated species, whereas eastside grassland has only 34. Sites dominated by native plants have more closely associated species than sites dominated by exotics (34 species closely associated with eastside grasslands vs. 2 with modified grasslands). Available water is a defining factor in these arid and semi-arid habitats, and this strongly shapes the composition of plant communities" and influences the ecology and behavior of associated wildlife. In Washington, precipitation occurs primarily during late autumn and winter with annual totals ranging from 5.9 inches (150 mm) in the lowest parts of the Columbia Basin to 21.7 inches (550 mm) in the higher elevations near the forest ecotone. Annual snowfall can be substantial at higher elevations and snow can remain in colder areas into spring. Growth of vegetation in spring is affected by available soil moisture, a result of "bioyear" precipitation--water that falls as rain or snow from October-April and is stored in the soil.22 Bioyear precipitation varies widely from year to year, affecting plant growth"' and influencing both forage for herbivorous wildlife and populations of herbivorous insects that form the food base for many reptiles and breeding birds. The marked seasonality in precipitation creates a flush of available food in spring and early summer that is capitalized on by breeding birds. In the lower rainfall zones most vegetative growth is completed by early summer and many plants senesce in preparation for the dry, hot months ahead. Related links:
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