PARENT SESSION
Oral Session #29: Invasions: Predicting and understanding invasibility. Presiding: K. Kearns.
Tuesday, August 7, 2001. 1:00 PM to 4:45 PM. Madison Ballroom C.

Environmental stress and plant community invasibility in a coastal grassland in California.

Kolb, Annette¹, Alpert, Peter¹, Enters, Dirk¹, Holzapfel, Claus¹, ¹

ABSTRACT- Grasslands at the University of California Bodega Marine Reserve show patchy invasion by non-native plant species. We hypothesized that low levels of resource availability or other types of environmental stress reduce invasibility in certain microsite types within this community by increasing the competitive ability of native grasses relative to non-natives. We predicted that the relative abundance of natives would be greater where soils were drier, less fertile, or more saline and that increasing stress would increase the relatively competitive ability of natives. Field surveys indicated that natives were relatively abundant where water or nutrient availabilities were lower, but that soil salinity had no effect on invasion. In greenhouse experiments, low nitrogen availability increased the competitive ability of the native grass Hordeum brachyantherum relative to the non-native grass, but low water availability did not. We conclude that low resource availability in certain microsites within plant communities can make these microsites less invasible and that effects of resource availability on competition between natives and non-natives is one mechanism by which resource heterogeneity can produce patchiness in invasion.

KEY WORDS: coastal grassland, plant competition, invasive species, environmental stress