ARS | Publication request: Rangeland Biodiversity: Do Realistic Species Losses Alter Ecosystem Function and Invasion Risks?

Submitted to: Society of Range Management
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2006
Publication Date: February 1, 2007
Citation: Rinella, M.J., Pokorny, M.L. 2007. Rangeland Biodiversity: Do Realistic Species Losses Alter Ecosystem Function and Invasion Risks?. Society of Range Management Abstract #364.

Technical Abstract: There is major concern that declining biodiversity could promote exotic species invasions. Consequently, many studies have evaluated invader responses to diversity treatments. Often, these treatments are instituted by randomly assigning species to synthetic plant communities or deleting randomly selected species from naturally occurring plant communities. This randomization contrasts with nature, where species losses are expected to be anything but random, and consequently, diversity-invasibility studies are sometimes criticized for lacking realism. An alternative approach to studying diversity-invasibility relationships asks first: "what kinds of species losses are occurring" and then designs research specifically addressing these losses. This was our approach: We imposed treatments that mimic management-induced plant group losses common to bunchgrass habitats (i.e. removal of shallow- and/or deep-rooted forbs and/or grasses). 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, the plant groups we studied similarly suppress invader growth. With respect to preventing invasions, this implies that maintaining ecosystem function (i.e. overall productivity) is more important than maintaining the productivity of particular plant groups. However, maintaining productivity may mean maintaining all plant groups, because removing forbs from our plots reduced overall biomass production in two of three years. However, forb-removal plots yielded highest in another year, and this led us to posit that removing forbs may increase the productivity variance, as opposed to increasing or decreasing the productivity mean. A time series model suggested that increased productivity variation may sometimes encourage invasion by allowing colonizing invaders to grow large quickly. On the other hand, increased variation may sometimes discourage invasion by keeping invaders somewhat small for longer or by killing them outright through competition.