Plant community diversity and native plant abundance decline with increasing abundance of an exotic annual grass |
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Authors: | Kirk W Davies |
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Institution: | (1) United States Department of Agriculture, Agricultural Research Service, Eastern Oregon Agricultural Research Center, 67826-A Hwy 205, Burns, OR 97720, USA |
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Abstract: | Exotic plants are generally considered a serious problem in wildlands around the globe. However, some argue that the impacts
of exotic plants have been exaggerated and that biodiversity and other important plant community characteristics are commonly
improved with invasion. Thus, disagreement exists among ecologists as to the relationship of exotic plants with biodiversity
and native plant communities. A better understanding of the relationships between exotic plants and native plant communities
is needed to improve funding allocation and legislation regarding exotic plants, and justify and prioritize invasion management.
To evaluate these relationships, 65 shrub–bunchgrass plant communities with varying densities of an exotic annual grass, Taeniatherum caput-medusae (L.) Nevski (medusahead), were sampled across 160,000 ha in southeastern Oregon, United States. Environmental factors were
generally not correlated with plant community characteristics when exotic annual grass density was included in models. Plant
diversity and species richness were negatively correlated with exotic annual grass density. Exotic annual grass density explained
62% of the variation in plant diversity. All native plant functional groups, except annual forbs, exhibited a negative relationship
with T. caput-medusae. The results of this study suggest that T. caput-medusae invasions probably have substantial negative impacts on biodiversity and native plant communities. The strength of the relationships
between plant community characteristics and T. caput-medusae density suggests that some exotic plants are a major force of change in plant communities and subsequently threaten ecosystem
functions and processes. However, experimental studies are needed to fully substantiate that annual grass invasion is the
cause of these observed correlations. |
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