Contrasting effects of resource availability and plant mortality on plant community invasion by Bromus tectorum L
Adair, C., I. Burke and W. Lauenroth. 2008. Plant and Soil 302:103-115
Abstract
The positive effect of disturbance on plant
community invasibility is one of the more consistent
results in invasion ecology. It is generally attributed to
a coincident increase in available resources (due to
the disturbance) that allows non-resident plant species
to establish. However, most research
addressing this issue has been in artificial or highly
modified plant communities. Our goal in this study
was to investigate the interactive effects of resource
availability and plant mortality disturbance on the
invasion of natural plant communities. We conducted
a series of experiments that examined the response of
Bromus tectorum L., a highly invasive annual grass,
to experimentally created gradients of resource availability
[nitrogen (N) and water] and resident plant
species mortality. We found that B. tectorum biomass
was co-limited by N and water. Biomass at the end of
the growing season was a saturating function (i.e.,
increased to a maximum) of water, which determined
maximum biomass, and N, which determined the rate
at which maximum biomass was attained. Despite that
fact that plant mortality increased N availability, it
had a negative impact on invasion success. Plant
mortality also decreased foliar cover, standing dead
biomass, and soil cover by litter. In harsh environments,
removing foliar and soil cover may increase
germination and seedling stress by increasing soil
temperatures and water loss. Across all treatments, B.
tectorum success decreased with decreasing foliar
cover and standing dead biomass. This, in combination
with the strong limitation of B. tectorum biomass
by water in this experiment, suggests that our plant
mortality disturbance removed soil cover that may
have otherwise aided B. tectorum invasion into this
semi-arid plant community by reducing water stress.
Key Words
Cheatgrass, Exotic species, Invasive plants, Nitrogen, Disturbance, Water
