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ARS Home » Plains Area » Miles City, Montana » Livestock and Range Research Laboratory » Research » Publications at this Location » Publication #202615
Title: Grassland Invader Responses to Realistic Changes in Native Species Richness

Author
item Rinella, Matthew - Matt
item POKORNY, MONICA - MT STATE U
item REKAYA, ROMDHANE - U OF GA

Submitted to: Ecological Applications
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/29/2007
Publication Date: 7/1/2007
Citation: Rinella, M.J., Pokorny, M.L., Rekaya, R. 2007. Grassland Invader Responses to Realistic Changes in Native Species Richness. Ecological Applications 17(6):1824–1831.

Interpretive Summary: There is major concern that declining biodiversity could promote exotic species invasions. We tested to se if the kinds of species losses that occur in grasslands will tend to promote invasions. We removed different groups of wildflowers and grasses from grassland field plots. Then we introduced the notoriously invasive spotted knapweed. Per-unit yield, all of the plant groups in our study were similarly effective at suppressing spotted knapweed growth. This implies that, in preventing invasions, maintaining overall grassland yields is more important than maintaining the yield of particular plant group/s.

Technical Abstract: There is major concern that declining biodiversity could promote exotic plant invasions. Consequently, many studies have subjected colonizing invaders to a range of species richness levels in order to clarify the role of biodiversity in repelling invasions. These studies have provided critical insight. However, because the studies have been somewhat artificial with respect to real-world extinction scenarios, they can be of limited usefulness when it comes to setting conservation priorities. Specifically, randomization schemes have largely determined the species to be added or omitted from the experimental units, and this randomization contrasts with the real world, where species losses are anything but random. This being the case, we believe nonrandom extinction/depletion scenarios may justify direct empirical investigations. In practice these investigations would begin by asking “which groups of species are being lost” and then studies would be designed to elucidate consequences of these losses. This paper illustrates such an approach. We imposed treatments that mimic management-induced extinctions/depletions common to grassland habitats (i.e. removal of shallow- and/or deep-rooted forbs and/or grasses and/or cryptogam layers). Then we introduced and monitored the performance of a notorious invasive species (i.e. Centaurea maculosa Lam.). We found that, on a per-gram-of biomass-basis, each resident plant group similarly suppressed invader growth. Hence, with respect to preventing invasions, maintaining overall productivity is probably more important than maintaining the productivity of particular plant groups or species. But maintaining overall productivity may mean maintaining all plant groups because removing forbs decreased overall productivity in two of three years. Alternatively, removing forbs increased productivity in another year, and this led us to posit that removing forbs may inflate the temporal productivity variance as opposed to greatly affecting time-averaged productivity. In either case, overall productivity responses to individual plant group removals were inconsistent and fairly modest. And as such, it seems C. Maculosa invasions may be a consequence of multiple plant groups being depleted simultaneously. For example, if forbs and shrubs are herbicide-treated to increase grass forage production, and then grasses are overgrazed, this could greatly magnify invasion risks.