Dominance of native grasses leads to community convergence in wetland restoration |
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Authors: | Laurel Pfeifer-Meister Bitty A Roy Bart R Johnson Jeff Krueger Scott D Bridgham |
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Institution: | (1) Institute of Ecology and Evolution, University of Oregon, Eugene, OR 97403-5289, USA;(2) Department of Landscape Architecture, University of Oregon, Eugene, OR 97403-5234, USA;(3) Lane Council of Governments, Eugene, OR 97401, USA |
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Abstract: | Wetland restoration is a pressing conservation priority, but there are few replicated field studies that provide a scientific
foundation for these activities. We conducted a 3-year, replicated field experiment to examine the effectiveness of initial
site preparation techniques (combinations of solarization, herbicide, tilling, and thermal weed control) in restoring native
plant biodiversity to an agricultural field in a former wetland prairie in Oregon, USA. Post-treatment, plots were sown with
a typical restoration mix of native graminoids and forbs. Treatments were compared to three high-quality managed reference
wetlands and the adjacent agricultural field. Site preparation treatments varied in their effectiveness in suppressing extant
vegetation and eliminating the residual seed bank. After 1 year, the solarization and fall herbicide application treatments
were the most effective at reducing exotic cover. However, after 3 years, plant community composition converged in all treatments
due to a loss of annual species and increasing dominance of native perennial bunchgrasses. Plant community composition became
more similar to the reference wetlands each year, but diversity and richness diverged, apparently due to a trade-off between
the cover of the dominant native bunchgrasses and diversity. Successional theory offers insights into how priority effects
and competitive inhibition may influence community trajectories, and offers a useful model for restoring plant communities
with high native diversity and dominance. Finding ways to mitigate the tradeoff between native plant cover and diversity by
actively managing successional trajectories is an important challenge in wetland restoration that deserves further investigation. |
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