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Self-Guided Plant Walks

Buck Island/ Al Borlin Park — March 2004
By Holly Zox

Our recent floods dramatically illustrate the dynamic nature of riparian ecosystems. During times of high water, Buck Island at the confluence of Woods Creek and the Skykomish River in Monroe is mostly under water. The riparian zone is an interface between aquatic and terrestrial ecosystems and can include the stream channel and surrounding, periodically inundated floodplains. Eighty-five to ninety percent of our wildlife species inhabit this productive area at some point in their lives.

Begin the walk at the Lewis Street entrance, just north of the bridge over the Skykomish River. Look down over the floodplain, river, and creek, and off to the mountains that are the source of the river. Patterns reflect interactions between climate, topography, soils, vegetation, and disturbance. Notice the physiognomy, or form, of the floodplain vegetation. Deciduous trees and shrubs predominate. Regular flooding results in a high light, high moisture environment that supports deciduous communities. A glance at the surrounding upland reveals the evergreen conifer forests more typical to our climate. Next, notice abundant mineral sediments washed up onto the land. Buck Island is in a low-gradient valley and fluvial, or stream, processes such as sediment deposition, flowing floodwaters, and channel migration have a strong impact on vegetation establishment. Cut banks and point bars are formed by the speed differential of water. Faster outer currents scour outside edges of curving channels, resulting in the undercut banks visible here, and deposit material along the inside, slower moving areas, resulting in the gravel bars that can be seen and explored on this walk. The cut banks create pools, which are habitat for aquatic organisms, while the point bars open up new land for plant succession. Last, notice large woody debris (LWD) both on land and in the water. One function of LWD on land is providing crucial structural habitat for the establishment of conifers within floodplains. A few Sitka spruce (Picea sitchensis), western hemlock (Tsuga heterophylla), and western redcedar (Thuja plicata) can be seen rising out of the deciduous floodplain forest. In water, LWD provides physical habitat for plants and animals, alters in-stream habitat by creating pools, riffles, shade, and hiding places, adds nutrient and energy sources, and can decrease erosion. Both upland and floodplain forests contribute LWD.

Now walk the bridge across Woods Creek and enter the forest on the fork of trail that runs along the Skykomish River. Riparian plants provide shade to keep streams cooler, which results in higher dissolved oxygen levels, fall in as LWD, add nutrient and energy sources as litter and bugs fall in, help control erosion, provide flood control by slowing flood waters, and are habitat for animals. To survive, riparian plants must be adapted to fluctuating water levels, withstand big floods, and have multiple methods of reproduction.

The dominant tree species of Buck Island are bigleaf maple (Acer macrophyllum) and black cottonwood (Populus balsamifera ssp. trichocarpa). Black cottonwood times its seed dispersal to coincide with traditional times of low water to take advantage of exposed mineral soil. It also sprouts from shed branch tips, broken branches, buried stems, and stumps. Snowberry (Symphoricarpos albus), abundant in the understory, tolerates fluctuating water tables. Scouler’s corydalis (Corydalis scouleri) rises out of a carpet of waterleaf (Hydrophyllum tenuipes). Both grow from thick rhizomes and spread vigorously. Piggyback plant (Tolmiea menziesii) also grows from rhizomes and can root from buds at the base of leaves. The trail is soon rerouted as last year’s trail falls abruptly into the river. Floods and storms repeatedly wash parts of the cut bank and plants living and dead into the river here. Look into the bank and see enormous deep roots that help hold plants in place. Bear right at a junction with the Woods Creek trail and take the next right fork for more river access and a close-up view of a gravel bar. Go back in time to earlier succession stages. Here see willows (Salix sp.) and young cottonwoods colonizing the gravel bar.

Continue east along the river and follow anglers’ paths under the old railroad trestle for a good view of a backwater channel. Faster flowing water carries larger sediments. Notice the cobble bar out in the faster currents and sand bar in the slow backwater channel. Backwater channels provide important rearing habitat for juvenile salmon. Visit again when salmon are spawning. The aroma in the forest, as salmon bring marine nutrients inland, is but one example of streams as ecological corridors.

Complete the loop by returning along Woods Creek. Travel north on the gravel road and alternate park entrance to a gate across from a Honey Bucket and follow the trail west along Woods Creek. Notice pools and ripples and more of the same riparian vegetation. Notice also houses filling the uplands. Streams are integrators for everything that happens in their watersheds. The replacement of upland forest (continuing far upstream) with impervious surfaces increases water level fluctuations due to increased stormwater runoff. Fewer species of plants and native amphibians have adapted to high water level fluctuations, so species richness in altered wetlands is typically low.

Streams and surrounding floodplain forest are corridors for native plants and animals, and also for exotics. Nearly every species of exotic invasive grows throughout the park. Back at the Woods Creek bridge, admire the efforts of the Forest and Stream Restoration Project. Join the city of Monroe and Stilly-Snohomish Fisheries Enhancement Task Force in one of their work parties to combat Bohemian knotweed (Polygonum x bohemicum).

Allow two hours for this easy two mile walk. Directions: from Highway 2 in Monroe, drive south on Lewis Street (Highway 203) to the Lewis Street Park just north of the bridge over the Skykomish River. Park in the lot on the east side of the road and find the trailhead behind the restrooms.