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The Cedar River Watershed is home to a wide variety of flowering plants, shrubs and trees; cone-bearing trees; and ferns. These are known as vascular plants because they have a structural system for carrying water and minerals throughout the plant.
Vegetation zones in the watershed are closely tied to elevation, which ranges from about 500 feet above sea level at Landsburg to 5,400 feet at Meadow Mountain at the Cascade Crest. The watershed is wet: rainfall varies from about 57 inches per year (mostly as rain) at Landsburg to more than 100 inches per year (mostly as snow) at the Cascade Crest.
Altitudinal effects are pronounced because precipitation increases and temperature decreases with higher elevations, resulting in pronounced cold temperatures and deep snow conditions at high elevations.
At the lowest elevations, conifer forests are dominated by:
With increasing altitude, forests become dominated by Pacific silver fir (Abies amabilis) and noble fir (Abies procera). At the highest elevations, these change to forests of subalpine fir (Abies lasiocarpa) and mountain hemlock (Tsuga mertensiana).
While vegetation is typical of the mid-Cascades in Washington, the current flora also is affected by the watershed’s location at the junction of the North Cascades Province and the South Cascades Province. These two provinces are distinguished by significantly different geologic histories and topographic origins, which, in turn, have influenced the floras found there.
Mountain uplift, volcanic action, and several rounds of glacial advances and recessions, along with significant diversification of climate, have acted as selection forces on potential floras originating from the south, the north (circumpolar and cordilleran), the east (the Columbia Basin), and the west (amphi-Pacific). These histories, origins, and forces have resulted in the floristic diversity that exists now.
Except for the most common plants, the vascular plant flora of the watershed was poorly known until 2001 and 2002, when the first systematic survey of vascular plants was undertaken. Since that time additional botanical surveys, monitoring and research projects, and observations by watershed staff have brought the total number of identified vascular plant species in the watershed (pdf) to 571. Over 80% of these are native plants, and 83% have been deposited at the University of Washington Herbarium.
Because Rattlesnake Mountain and Rattlesnake Ledges exceeded the maximum height of the Cordilleran ice sheets during the last ice age, they were refuges to plants and animals during that time. A notably unique and diverse plant community is now found on the Rattlesnake Ledges.
Examples of dry coastal or interior species occurring on the Rattlesnake Ledges include:
The Ledges also support populations of two naturally occurring hybrid species:
This large wetland is characterized by deep, saturated organic soils and a flora characteristic of bogs and fens. Unusual plants found here include:
This is also one of just a few known locations globally of the very rare Beller’s ground beetle (Agonum belleri).
Several plant species occurring in the watershed are notable for being unusual. For example, a population of the few-flowered reed grass (Calamagrostis sesquiflora) from rock outcrops in the watershed is the only known station of that species in King County.
Surveys identified several species included on the Washington Natural Heritage Program’s Watch List of Vascular Plants:
No species tracked as rare plants by the Heritage Program have been found in the watershed.
As settlers of European and Asian descent arrived in the watershed in the 1870’s, invasive alien plant species soon followed. Over the last 120 years or so of mining, building roads and settlements, and timber extraction, numerous non-native plant species were introduced to the watershed.
Most of these species are relatively harmless, but several threaten to cause ecological damage by eliminating native biological diversity or infesting important wetland and riparian habitats.
Nine species of non-native invasive plants in the watershed are currently legally required to eradicate or control. An additional 22 species are not legally required to control, but pose significant ecological risk. These species are controlled if they are limited in extent or where they occur in high value habitats such as wetlands, meadows, and riparian areas.
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Habitats in the Cedar River Watershed: