PARENT SESSION
Oral Session #28: Invasions - Resistance and facilitation.
Presiding: D. Holway
Tuesday, August 6. 8:00 AM to 11:30 AM. Gila Meeting Room, TCC.
Diversity and invasibility in immigration-driven southern Appalachian riparian plant communities.
BROWN, REBECCA*,1, 1 University of North Carolina at Chapel Hill, Chapel Hill, NC
ABSTRACT- I propose that the relationship between diversity and community invasibility depends on the degree to which community composition is driven by immigration versus extinction processes. Such processes include moderate disturbance and propagule pressure, which increase immigration, whereas competition and environmental stress limit community composition by creating local extinctions or inhibiting new species colonization. I expect that high rates of propagule pressure combined with disturbance due to flooding cause riparian plant communities to be disproportionately driven by immigration processes. I explored the role that immigration processes play in structuring riparian plant communities using multi-scale vegetation plots and seed traps stratified by geomorphic position in riparian areas and adjacent uplands of the Little Tennessee, Upper New, and Nolichucky Rivers in Western North Carolina. I assessed patterns of riparian vegetation composition and propagule pressure and compared native and exotic vascular plant species diversity at large and small spatial scales in riparian and upland communities. Species composition varied among the three rivers, but was consistently correlated with geomorphic position and soil fertility. Propagule species richness and abundance were correlated with flooding. At the 100-m2 scale, the relationship between native and exotic species richness in riparian areas was positive, whereas there was no relationship in uplands. However, at the 0.01-m2 scale, there was a negative relationship between native and exotic diversity in riparian areas, likely as a result of community saturation at small spatial scales.
KEY WORDS: invasibility, southern Appalachian, immigration-extinction gradient, riparian