PARENT SESSION
Poster Session 7: Invasive Species.
Monday, August 2 Presentations from 5:00 PM to 6:30 PM, Exhibit Hall A 1.
Holcus lanatus invasion slows decomposition through its interaction with an important detritivore, Porcellio scaber.
Bastow, Justin *,1, Strong, Don1, Preisser, Evan1, 1 University of California-Davis, Davis, CA
ABSTRACT- Invasive species may alter ecosystem processes through their impact on the density and behavior of resident species. Holcus lanatus is an invasive perennial grass in the coastal prairie of California. At the Bodega Marine Reserve, the dominant macrodetritivore is the isopod Porcellio scaber. We used litter bags to determine if H. lanatus, through its interaction with P. scaber, lead to differences in litter decomposition rates between invaded and uninvaded prairie. We transplanted litter from H. lanatus, resident grasses and Lupinus arboreus, the dominant shrub in the system, into three sites in September of 2002. Half of the litter bags were retrieved in March of 2003 in order to measure the rate of decomposition during the winter, while half of the litter bags were left until September 2003 to measure total annual decomposition. Although there was no effect of isopods on litter mass loss during the winter, when most decomposition occurred, isopods had substantial effects on litter loss during the summer. By the end of 12 months, litter loss of H. lanatus was 16% less than that of resident grasses. The difference was attributable primarily to the preferences of P. scaber, which avoided H. lanatus litter. This suggests that H. lanatus invasion slows decomposition in the coastal prairie through its interaction with an important resident detritivore. Simple linear projections of litter accumulation suggest that this change in decomposition rates would lead to a 28% increase in standing litter biomass at the end of the growing season.
Key words: biological invasions, seasonality, decomposition, litter dynamics