Mechanisms underlying the impacts of exotic annual
grasses in a coastal California meadow |
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Authors: | Heather M Coleman Jonathan M Levine |
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Institution: | (1) Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA;(2) Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, CA 93106-9610, USA;(3) Bren School of Environmental Science and Management, University of California, Santa Barbara, CA 93106-5131, USA |
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Abstract: | Biological invasions can impact the abundance and diversity of native species, but the specific mechanisms remain poorly discerned.
In California grasslands, invasion by European annual grasses has severely reduced the quality of habitat for native forb
species. To understand how introduced grasses suppress native and exotic forbs, we examined the response of a Southern California
grassland community to factorial removals of live grass and the litter produced in previous seasons. To examine the role that
belowground competition for water plays in mediating the impact of grasses, we crossed grass and litter removal treatments
with water addition. Our results show that forbs were almost equally suppressed by both competition from live grass and direct
interference by litter. Water addition did not ameliorate the effect of grass competition, suggesting that water was not the
resource for which plants compete. This evidence is consistent with the susceptibility of forbs to light limitation, especially
considering that litter does not consume water or nutrients. Interestingly, despite different histories of co-occurrence with
annual grass dominants, native and exotic forbs were comparably suppressed by exotic grasses. Our results indicate that suppression
by both live and dead stems underlie the influence of exotic grasses on forb competitors. |
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Keywords: | Competition Grass Forb Invasion Invasive species Santa Monica Mountains |
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