Okanagan dry forests
Okanagan dry forests are an ecoregion located in inland western North America, primarily spanning south-central British Columbia and north-central Washington State. This biome is characterized by hot, dry summers and moderately cool winters, with annual precipitation varying significantly based on elevation. The region features a mix of grasslands, low-elevation dry forests, and conifer forests predominantly composed of Douglas fir and ponderosa pine, while lower valleys often transition into shrub-steppe and grassland ecosystems. The south Okanagan Valley, notable for its desert-like characteristics, supports diverse wildlife, including approximately 190 bird species and various mammals like California bighorn sheep and black bears.
Fire plays a critical role in maintaining the health of these forests, though human activities and climate change pose significant challenges. Lightning is the main natural cause of forest fires, but increasing temperatures and drought conditions are leading to more intense and destructive wildfires. As urban expansion and agricultural development continue to alter the landscape, only a small portion of the original habitat remains intact. The ongoing effects of climate change are expected to intensify the ecological pressures on these forests, affecting species dynamics and habitat preservation. Understanding the complex interplay between natural processes and human impact is essential for the conservation of the Okanagan dry forests and their unique biodiversity.
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Okanagan dry forests
- Category: Forest Biomes.
- Geographic Location: Western North America.
- Summary: This ecoregion includes alpine forests and grasslands of varying types; a major concern is the human interaction with fire regimes.
The Okanagan Dry Forests biome is found in inland western North America, with about 65 percent of the region in south-central British Columbia and 35 percent in north-central Washington State. The ecoregion is situated between the Rocky Mountains to the east, and the Coastal Ranges to the west. Impacted by the hot, dry air of the Canadian Basin and the colder, arctic air to the north, this region encompasses both the coldest climate in Washington, and some of the hottest and driest climate of British Columbia.
This biome is characterized by very warm to hot, dry summers and moderately cool winters with little snowfall. Average summer temperatures range from 59 to 62 degrees F (15 to 16.5 degrees C); and average winter temperatures are about 28 degrees F (minus 2.5 degrees C). Precipitation ranges from 10 inches (25 centimeters) to over 39 inches (100 centimeters) per year, depending on elevation.
Biodiversity
This area includes areas of grasslands and low elevation dry forests, as well as conifer forests. The conifer forests consist primarily of Douglas fir and ponderosa pine. Some areas sustain stands of lodgepole pine (Pinus contorta), quaking aspen (Populus tremuloides), white spruce (Picea glauca), grand fir (Abies grandis), and western larch (Larix occidentalis). These forests change to shrub-steppe in the valleys in the eastern part, and grasslands in the western portion of the region. The desert-like south Okanagan Valley is one of the most remarkable grasslands in British Columbia. It is not quite dry enough and too cold on average to be a true desert, and is more correctly termed a shrub-steppe. Nevertheless, its cacti, rattlesnakes, and scorpions hint at its relationship to the true deserts of the southwestern United States.
Dry desert sage brush and conifer trees provide abundant habitat for the many bird species found here. Approximately 190 species of birds breed in the south Okanagan. Animal habitat is diverse, and supports species such as the California bighorn sheep, mountain goat, mule deer, black bear, cougar, coyote, bobcat, grouse, and California quail.
This diverse ecosystem has several species classified as threatened or endangered, including the badger, tiger salamander, burrowing owl, pallid bat, Behr’s hairstreak butterfly, night snake, Grand Coulee owl-clover, Great Basin spadefoot toad, western rattlesnake, lark sparrow, northern Pacific rattlesnake, Swainson’s hawk, long-billed curlew, interior western screech-owl, yellow-breasted chat, brewer’s sparrow, grasshopper sparrow, badger, and Great Basin gopher snake. Preserving this habitat is essential for their continued survival.
Human Impact
Lightning is the primary non-human cause of forest fires in the area, causing more than 50 percent of fires in western Canada and the Northwest Territories. High temperatures, low humidity, and extended periods of drought added to high lightning probability can produce significant fires. Forest fires are not necessarily bad, and can in fact lead to the health of the forest. A fire within the forest will remove the tallest and most mature growth.
Also removed with this loss is the susceptibility of disease and insect infestation in mature trees. Leaves and debris found on the forest floor are removed with a surface fire, allowing the growth of new saplings. However, there is often public concern when wildfires burn unrestricted, that is, with no human intervention.
Research indicates that the future climate of these dry forests and conditions throughout the Canadian west will continue to become drier and warmer in the coming years. Fires that were once smaller, cooler, and more frequent have become larger and more intense, destroying resources and natural habitat. As a result, it is predicted that forest fires within Canada, including British Columbia, can be expected to increase over the next century. Some major fires of the area included the 2003 Okanagan Mountain Park fire and the 2017 British Columbia wildfires.
It is estimated that only about 20 percent of the Okanagan Dry Forest ecoregion remains as intact habitat. Some areas have been heavily altered due to growing urban expansion, conversion of land into agricultural production, and uncontained wildfire. This is particularly true of the valleys and basins. Upper elevations have been impacted more by livestock grazing, logging, open pit mines, agriculture, and transmission and pipeline corridors.
Some grasslands have been seriously overgrazed by livestock. Climate change is already impacting the forests here: warmer temperatures affect tree growth rates, mortality rates, disturbance patterns (such as storms, drought, fire), and the distribution of tree species after disturbances. Impacts are cumulative and interconnected. For example, drought can stress trees, making them more susceptible to attack by insects and disease.
Bibliography
Brookes, Wesley, et al. "A Disrupted Historical Fire Regime in Central British Columbia." Frontiers in Ecology and Evolution, 28 June 2021. DOI: 10.3389/fevo.2021.676961. Accessed 20 Nov. 2024.
Hessburg, Paul F. and James K. Agee. “An Environmental Narrative of Inland Northwest United States Forests, 1800–2000.” Forest Ecology and Management 178 (2003).
Ness, Reed. “Okanogan Dry Forests.” One Earth, www.oneearth.org/ecoregions/okanogan-dry-forests/. Accessed 20 Nov. 2024.
Pacific Northwest Research Station. DryForests of the Northeastern Cascades Fire and Fire Surrogate Project Site, Mission Creek, Okanogan-Wenatchee National Forest. Portland, OR: United States Department of Agriculture—Forest Service, 2009.
The Partnership for Water Sustainability in British Columbia. “Geographical Analysis of Cumulative Threats to Prairie Water Resources: Mapping Water Availability, Water Quality, and Water Use Stresses.” www.scirp.org/reference/referencespapers?referenceid=45983. Accessed 20 Nov. 2024.