Document Type

Project

Publication Date

Spring 2001

Keywords

Riparian ecosystems, Riparian restoration, Nooksack Salmon Enhancement Association

Abstract

Riparian corridors are complex and diverse ecosystems that are essential to the maintenance of global health. The total area occupied by riparian ecosystems in the United States has plummeted in the last 200 years to only 20% of its initial size. The recent movement to restore these fragile and complex ecosystems has produced outcomes of variable success. The Nooksack Salmon Enhancement Association’s riparian restoration project at Schell Creek in Femdale, WA provides an example of an effort that exhibits mixed results. Our experiment explored reasons for the variable success of the restoration vegetation and investigated several ecosystem factors that may limit growth of seedlings at this site. These included competition from grasses, low nutrient availability, lack of mycorrhizal associations, and water availability.

In May of 2000, seedlings of red alder {Alnus rubra) and Sitka spruce {Picea sitchensis) were planted in a full factorial design with treatments consisting of tilling to reduce competition (T), mycorrhizal inoculation (M), and nutrient supplementation in the form of fertilizer (F). Three replicate blocks of each treatment were situated in both the upper (north) and lower (south) reaches of the project, which differed in water availability. We assessed differences between treatment effects by comparing changes in tree heights, total growth, and photosynthetic rates (determined using a LI-COR 6400).

While we had hypothesized that increased water availability in the upper reach helped revegetation success, the excess soil moisture actually appeared to have negative effects on experimental seedlings: waterlogging caused poor growth and mortality in some cases, leading to negligible treatment effects in the upper reach. Reducing grass competition by tilling, which increased the water and nutrients available to experimental trees, had the largest positive effect on alder growth in the south site. Mycorrhizae had a positive effect on spruce growth, although these effected were muddled by interactions with tilling and fertilizer treatments, which have both been shown to have negative effects on the success of mycorrhizae.

Reducing competition is a technique used widely in riparian restoration, a practice whose benefit is bolstered by the observed considerable effect of tilling on experimental trees at the Schell Creek site. As the use of mycorrhizae as a restoration tool is not common procedure, our results suggest that future studies should continue to explore the advantages of this treatment, especially when planting in low nutrient areas. Current restoration recommendations emphasize the importance of assessing abiotic conditions before selecting project sites and restoration vegetation, and we agree given the very different treatment responses of our experimental species and the environmental variability at the site. We believe that further development of these techniques will continue to enhance project success, thereby providing a substantial contribution to the strong movement afoot to reestablish riparian ecosystems in Whatcom County and elsewhere.

Department

Environmental Sciences

Subjects - Topical (LCSH)

Riparian ecology--Washington (State)--Schell Creek Region (Whatcom County)

Geographic Coverage

Schell Creek Region (Whatcom County, Wash.)

Genre/Form

student projects; term papers

Type

Text

Rights

Copying of this document in whole or in part is allowable only for scholarly purposes. It is understood, however, that any copying or publication of this document for commercial purposes, or for financial gain, shall not be allowed without the author’s written permission.

Rights Statement

http://rightsstatements.org/vocab/InC/1.0/

Language

English

Format

application/pdf

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