Role of a Native Legume in Facilitating Native vs. Invasive Species in Sagebrush Steppe Before and After Fire
Goergen, E.. 2008. Dept. of Natural Resources and Environmental Science. University of Nevada, Reno, NV
Abstract
In the semi-arid sagebrush steppe of the Northeastern Sierra Nevada, resources
are both spatially and temporally variable, arguably making resource availability a
primary factor determining invasion success. N fixing plant species, primarily native
legumes, are often relatively abundant in sagebrush steppe and can contribute to
ecosystem nitrogen budgets. Lupinus argenteus (Pursh), a native legume abundant in
high elevation areas of western North America, is one of the most common native
legumes in sagebrush steppe. L. argenteus responds positively to disturbance and prior
studies indicate that it can increase the availability of soil nitrogen. Thus contribution of
nitrogen by L. argenteus can potentially have a large effect on maintaining native species
diversity and productivity of sagebrush ecosystems. However, if a non-native seed
source is present, increased nitrogen associated with L. argenteus can create conditions
favorable for invasion by non-native species. This study examined the role of L.
argenteus on resource availability in the sagebrush steppe and the implications for
invasion with four interrelated studies. Results indicate that L. argenteus can modify
available soil N and increase productivity in sagebrush ecosystems both through
rhizodeposition and litter decomposition. Further, modification of the local resource pool
by L. argenteus can alter competitive outcomes among native and non-native species and
can increase plant establishment and growth of both native and non-native species.
However, higher establishment and growth rates give the non-native a greater advantage.
The ability of L. argenteus to increase N availability can serve to promote resilience of
native ecosystems, but also may create an avenue for invasion.
