HR: 1340h
AN: B23A-0952    [Abstracts]
TI: An Invasive Grass Species Alters Carbon Cycling in Hawaiian Dry Forest
AU: * Litton, C M
EM: clitton@fullerton.edu
AF: California State University Fullerton, Department of Biological Sciences 800 N. State College Blvd, Fullerton, CA 92834 United States
AU: * Litton, C M
EM: clitton@fullerton.edu
AF: USDA Forest Service, Institute of Pacific Islands Forestry 23 E. Kawili St, Hilo, HI 96720 United States
AU: Sandquist, D R
EM: dsandquist@fullerton.edu
AF: California State University Fullerton, Department of Biological Sciences 800 N. State College Blvd, Fullerton, CA 92834 United States
AU: Cordell, S
EM: scordell01@fs.fed.us
AF: USDA Forest Service, Institute of Pacific Islands Forestry 23 E. Kawili St, Hilo, HI 96720 United States
AB: At lower elevations on the leeward side of the island of Hawaii, remnant native forests are heavily invaded by an introduced African bunchgrass, {\it Pennisetum setaceum} (fountain grass). Our research is designed to determine the consequences of this invasion for carbon (C) cycling in Hawaiian dry forests. We examined above- and belowground C pools and fluxes in 400 m$^{2}$ replicated forest plots ({\it n} = 4) with fountain grass (grass plots) and in areas where fountain grass had been removed for $\sim$3 years (removal plots). C pools were estimated with direct sampling and allometric equations developed {\it in situ} for the dominant tree species. Aboveground net primary productivity (ANPP) was estimated as aboveground biomass increment plus litterfall minus loss from mortality (trees) and with clip plots (grass and herbaceous species); total belowground carbon allocation (TBCA) was estimated using a conservation of mass, C balance approach. Our results indicate that the invasion of a non-native grass in this ecosystem has considerable impacts on both C pools and fluxes. Aboveground, tree biomass did not differ between treatments ({\it P} = 0.57) but the presence of fountain grass led to a 7.5-fold increase in understory biomass in grass plots compared to removal plots ({\it P} $<$ 0.01). Tree ANPP was significantly higher in removal plots for both foliage (0.10 and 0.06 kg C m$^{-2}$ yr$^{-1}$ for removal and grass plots, respectively; {\it P} = 0.02) and wood (0.13 and 0.05 kg C m$^{-2}$ yr$^{-1}$ for removal and grass plots, respectively; {\it P} $<$ 0.01). However, grass ANPP was $\sim$35% greater than tree foliage productivity in grass plots. Despite this added foliar productivity, total ANPP (Tree + Grass ANPP) was significantly higher in removal plots ({\it P} = 0.04). Belowground, grass plots exhibited higher rates of soil-surface CO$_{2}$ efflux (1.09 and 1.38 kg C m$^{-2}$ yr$^{-1}$ for removal and grass plots, respectively; {\it P} = 0.03 ). Likewise, TBCA was significantly higher in grass plots (1.21 kg C m$^{-2}$ yr$^{-1}$) than in removal plots (0.97 kg C m$^{-2}$ yr$^{-1}$; {\it P} = 0.04). Tropical dry forests globally, and Hawaiian dry forests in particular, are among the most threatened terrestrial ecosystems. Our results indicate that the presence of an invasive, non-native grass species changes both ecosystem structure and function in these forests. These changes in above- and belowground C pools and fluxes are particularly important in light of the ubiquitous presence of invasive species in most terrestrial ecosystems and the need for a better understanding of the role that they will play in global C cycling and climate change.
DE: 1600 GLOBAL CHANGE (New category)
DE: 1615 Biogeochemical processes (4805)
DE: 0400 Biogeosciences
SC: Biogeosciences [B]
MN: 2004 AGU Fall Meeting