Introduced annuals mediate climate-driven community change in Mediterranean prairies of the Pacific Northwest, USA
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Date
2021-11-01
Authors
Reed, Paul B.
Pfeifer-Meister, Laurel E.
Roy, Bitty A.
Johnson, Bart R.
Bailes, Graham T.
Nelson, Aaron A.
Bridgham, Scott D.
Journal Title
Journal ISSN
Volume Title
Publisher
Wiley
Abstract
Aim: How climate change will alter plant functional group composition is a critical
question given the well-recognized
effects of plant functional groups on ecosystem
services. While climate can have direct effects on different functional groups, indirect
effects mediated through changes in biotic interactions have the potential to
amplify or counteract direct climatic effects. As a result, identifying the underlying
causes for climate effects on plant communities is important to conservation and
restoration initiatives.
Location: Western Pacific Northwest (Oregon and Washington), USA.
Methods: Utilizing a 3-year
experiment in three prairie sites across a 520-km
latitudinal
climate gradient, we manipulated temperature and precipitation and recorded
plant cover at the peak of each growing season. We used structural equation models
to examine how abiotic drivers (i.e. temperature, moisture and soil nitrogen) controlled
functional group cover, and how these groups in turn determined overall plant
diversity.
Results: Warming increased the cover of introduced annual species, causing subsequent
declines in other functional groups and diversity. While we found direct effects
of temperature and moisture on extant vegetation (i.e. native annuals, native
perennials and introduced perennials), these effects were typically amplified by introduced
annuals. Competition for moisture and light or space, rather than nitrogen,
were critical mechanisms of community change in this seasonally water-limited
Mediterranean-climate
system. Diversity declines were driven by reductions in native
annual cover and increasing dominance by introduced annuals.
Main conclusions: A shift towards increasing introduced annual dominance in this
system may be akin to that previously experienced in California grasslands, resulting
in the “Californication” of Pacific Northwest prairies. Such a phenomenon may challenge
local land managers in their efforts to maintain species-rich
and functionally
diverse prairie ecosystems in the future.
Description
12 pages
Keywords
Climate manipulations, Diversity, Evenness, Functional groups, Invasion, Plant community, Richness, Soil moisture, Structural equation modelling, Warming
Citation
Reed, P. B., Pfeifer-Meister, L. E., Roy, B. A., Johnson, B. R., Bailes, G. T., Nelson, A. A., & Bridgham, S. D. (2021). Introduced annuals mediate climate-driven community change in Mediterranean prairies of the Pacific Northwest, USA. Diversity and Distributions, 27, 2584–2595. https://doi.org/10.1111/ddi.13426