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About SPU
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Water System
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Cedar and Tolt Watersheds
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Cedar River Biodiversity
Seed Plants & Ferns
Overview
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:
- • Douglas-fir (Pseudotsuga menziesii)
- • western hemlock (Tsuga heterophylla)
- • western redcedar (Thuja plicata).
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.
Surveys
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. This survey identified about 450 different species of vascular plants, using more than 500 collected specimens (now deposited at the University of Washington Herbarium). The survey provided information on the occurrence and distribution of rare and unusual plants, invasive alien plants, and culturally important plants.
Unusual Plant Communities
Rattlesnake Ledges
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:
- • Allium cernuum
- • Arctostaphylos columbiana
- • Lomatium martindalei
- • Ceanothus sanguineus
- • Psoralea physodes
The Ledges also support populations of two naturally occurring hybrid species:
- • Arctostaphylos media
- • Spiraea pyramidata
Eagle Ridge Fen
This large wetland is characterized by deep, saturated organic soils and a flora characteristic of bogs and fens. Unusual plants found here include:
- • two species of carnivorous plants (Utricularia vulgaris and Drosera rotundifloia)
- • a large, dominant population of sweet gale (Myrica gale)
This is also one of just a few known locations globally of the very rare Beller’s ground beetle (Agonum belleri).
Rare Plants
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:
- • Russet sedge (Carex saxatilis var. major), known from the margins of lakes, ponds, and tarns at subalpine elevations in the watershed. These are among the southernmost stations for this mostly boreal species.
- • Canby’s angelica (Angelica canbyi), known from wetland meadows.
- • Round-leaved rein-orchid (Platanthera orbiculata) has been previously collected, but has not been found in recent surveys.
- • Wool-grass (Scirpus atrocinctus), known from low elevation wetland meadows.
- • Pyramidal spirea (Spiraea pyramidata), known from rock outcrops at mid-elevations.
No species tracked as rare plants by the Heritage Program have been found in the watershed.
Invasive Alien Plants
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 road-building, mining, urban development, and timber extraction, numerous non-native plants have been 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.
These invasive alien species are currently the target of monitoring and management:
- • English ivy (Hedera helix)
- • European blackberries (Rubus armeniacus and R. laciniatus)
- • Eurasian water-milfoil (Myriophyllum spicatum)
- • Knotweeds (Polygonum species and hybrids)
- • Scot’s broom (Cytisus scoparius)
- • sycamore maple (Acer pseudoplatanus)
- • tansy ragwort (Senecio jacobaea)
- • yellow hawkweed (Hieracium caespitosum)
Reports and Citations
- • Vascular Plant Species List (PDF)
- • Franklin, J. F. and C. T. Dyrness. 1973. Natural vegetation of Oregon and Washington. USDA Forest Service. General Technical Report. Portland, Oregon.
- • Haugerud, R. A. 2004. Cascadia—Physiography. USGS Miscellaneous Investigations Map I-2689.
Contact Information
Contact clay.anteiau@seattle.gov
Related Links
For plants associated with a particular habitat in the Cedar River Watershed, see:
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