OOS 36-7 - A canopy trimming experiment in Puerto Rico: Effects on invertebrates, microbes and decay

Thursday, August 11, 2011: 10:10 AM
12A, Austin Convention Center
Grizelle González, International Institute for Tropical Forestry, San Juan, PR, D. Jean Lodge, Northern Research Station, USDA-Forest Service, Luquillo, PR, Sharon A. Cantrell, Universidad del Turabo, Gurabo, PR and Barbara Richardson, Luquillo Experimental Forest LTER, Puerto Rico, Edinburgh, United Kingdom

Hurricanes are major perturbations in Caribbean forests.  The transfer of canopy to the forest floor by hurricanes can alter biotic and biogeochemical processes.  Litterfall in the Luquillo Mountains of Puerto Rico from Hurricane Georges (1998) was 0.55 – 0.93 times the annual rate, resulting in a 120-250% increase in forest floor standing stocks. Litter standing stocks returned to normal within a year, but it was unclear if canopy opening and/or hurricane litter deposition had stimulated decomposition.  Thus, the Canopy Trimming Experiment (CTE) was designed to experimentally disentangle the effects of canopy opening vs. debris deposition resulting from hurricane disturbance on organismal and ecosystem responses in a subtropical wet forest.  We hypothesized that both factors, alone and together, modify detrital processing and nutrient release through their effects on litter invertebrate and microbial communities.  We present data from two simultaneous litter decay experiments (litterbags of different mesh sizes and litter decay baskets) and associated measures of microbial and invertebrate communities. 


Canopy opening initially resulted in major differences in microclimate between trimmed and untrimmed plots that diminished as the canopy recovered.  Soil and litter moisture levels responded differently to canopy trimming.  In trimmed plots, litter moisture initially decreased whereas soil moisture increased relative to untrimmed plots.  Differences in litter moisture were related to changes in the microbial composition of the decaying litter.  Though fungi:bacteria ratios in the decaying litter were not affected by canopy opening or biomass redistribution, basidiomycetes that degrade lignin decreased with canopy opening and increased with debris deposition while ascomyceteous microfungi increased with canopy opening.  The diversity of litter fungi was greater than that of the bacteria at the early stages of decay, while the inverse pattern was significantly evident at the latter stages.  Canopy opening significantly reduced invertebrate diversity and biomass, but not the overall abundance.  Individual taxa responded differently, resulting in community differences between trimmed and untrimmed plots.  Mites, collembolans, and psocopterans (microbiovores mainly feeding on microfungal hyphae and spores) responded positively to canopy opening whereas the abundance of all other taxa (larger detritivores and predators) declined.  The percent of mass remaining was significantly greater in trimmed plots than in untrimmed plots.  Fungal connectivity between the litter cohorts (mostly basidiomycetes) was reduced by drying in the trimmed plots, and was strongly correlated with reduced P accumulation and slower rates of decay.  These results suggest that disturbance has long-lasting effects on litter communities, which may affect detrital processing.


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