The climate is influenced by both the pacific maritime and continental air masses causing moisture on the windward side of the Coast and Cascade Ranges in both summer and winter and wind with high evaporation rates on the Plateau. The variation in topography, elevation and aspect significantly affect local climates. Merritt, has the hottest and driest climate in this grassland area with the average temperature in July equaling 18.2 degrees Celcius and annual precipitation averages of only 311 mm. The frost-free period averages 250 days, which is nearly triple that at Princeton.
Soils are generally dark brown and black chernozems in the grasslands with brunisols occuring in the Ponderosa Pine areas. Wetlands occur throughout the area along drainage channels and in depressions. Soils vary considerably from coarse textured Gleysols to Organics depending on the vegetation and drainage.
Grasslands are present in six biogeoclimatic zones and 13 variants on the Southern Thompson Uplands. Nearly 75% of the grasslands, however, are found in two variants in the Interior Douglas-fir Zone, and about 20% in the Bunchgrass Zone. Varying amounts of grassland totaling about 6500 ha are also found in the Ponderosa Pine, Montane Spruce, Interior Cedar Hemlock and Engelmann Spruce Sub-alpine Fir Zones
Big sagebrush co-dominates with widely spaced bluebunch wheatgrass plants and common rabbit-brush in lower elevation grassland communities. Needle-and-thread grass tends to replace bluebunch wheatgrass as dominant on dry sites with coarse-textured soils. In higher elevations of the Thompson Uplands a mixture of bluebunch wheatgrass and sandbergs' bluegrass at climax with lesser amounts of needle-and-thread grass and junegrass is present. Big sagebrush is usually absent.
A high diversity of wildlife including reptiles, birds and small mammals are found in the South Thompson Uplands. Wetlands common in the middle grasslands are home to the Great Basin spadefoot toad and long-toed salamander as well as numerous species of migratory and resident birds such as the Common Goldeneye, Canvasback and American Widgeon. Upland birds and raptors are found on the grasslands including the Black-billed Magpie, Eastern Kingbird and Long-billed Curlew.
There are also a number of grassland associated habitats in the Thompson Uplands that help to define grassland ecosystems. Aspen copses, for example, occur on level to gently sloping sites at lower slope positoins and in depressions in grassland environments. Aspen copses are critical for cavity nesters and also provide cover and forage during the winter months for species such as Sharp-tailed grouse.
*(Warning: HP files can be many megabytes in size - do not download unless you have access to an HP plotter)
Print This Page