A Canopy Trimming Experiment in Puerto Rico: The Response of Litter Invertebrate Communities to Canopy Loss and Debris Deposition in a Tropical Forest Subject to Hurricanes

Richardson, Barbara A.; Richardson, Michael J.; Gonzalez, Grizelle; Shiels, Aaron B.; Srivastava, Diane S. 2010. A canopy trimming experiment in Puerto Rico: the response of litter invertebrate communities to canopy loss and debris deposition in a tropical forest subject to hurricanes. Ecosystems. 13: 286-301.

Hurricanes cause canopy removal and deposition of pulses of litter to the forest floor. A Canopy Trimming Experiment (CTE) was designed to decouple these two factors, and to investigate the separate abiotic and biotic consequences of hurricane-type damage and monitor recovery processes. As part of this experiment, effects on forest floor invertebrate communities were studied using litterbags. Canopy opening resulted in increased throughfall, soil moisture and light levels, but decreased litter moisture. Of these, only throughfall and soil moisture had returned to control levels 9 months after trimming. Canopy opening was the major determinant of adverse changes in forest floor invertebrate litter communities, by reducing diversity and biomass, irrespective of debris deposition, which played a secondary role. Plots subjected to the most disturbance, with canopy removed and debris added, had the lowest diversity and biomass. These two parameters were higher than control levels when debris was added to plots with an intact canopy, demonstrating that increased nutrient potential or habitat complexity can have a beneficial effect, but only if the abiotic conditions are suitable. Animal abundance remained similar over all treatments, because individual taxa responded differentlyto canopy trimming. Mites, Collembola, and Psocoptera, all microbiovores feeding mainly on fungal hyphae and spores, responded positively, with higher abundance in trimmed plots, whereas all other taxa, particularly predators and larger detritivores, declined in relative abundance. Litterbag mesh size and litter type had only minor effects on communities, and canopy trimming and debris deposition explained most variation between sites. Effects of trimming on diversity, biomass, and abundance of some invertebrate taxa were still seen when observations finished and canopy closure was complete at 19 months. This suggests that disturbance has a long-lasting effect on litter communities and may, therefore, delay detrital processing, depending on the severity of canopy damage and rate of regrowth.

A Comparison of Two Sampling Strategies to Assess Discomycete Diversity in Wet Tropical Forests

CANTRELL, SHARON A. 2004. A Comparison of Two Sampling Strategies to Assess Discomycete Diversity in Wet Tropical Forests. Caribbean Journal of Science, Vol. 40, No. 1, 8-16, .

Most of the fungal diversity studies that have used a systematic collecting scheme have not included the discomycetes, so optimal sampling methods are not available for this group. In this study, I tested two sampling methods at each sites in the Caribbean National Forest, Puerto Rico and Ebano Verde Reserve, Dominican Republic. For a plot-based sampling method, 10 × 10 m plots were established and divided into one hundred 1 × 1 m subplots. For each sample, 12 subplots were selected at random with replacement. For a transect-based sampling method, 60 m long transects were established with twelve 1 × 1 m subplots randomly placed on either side of the transect line at 5 m intervals at the beginning of the study. The study was conducted from October 2001 to September 2002. For Puerto Rico, 46 and 51 morpho-species were identified in the transects and plots, respectively. There was a 32% overlap (68% complementarity) between sites. The Sorensen Similarity Coefficient between sites was 0.50 for both methods, and 0.55-0.63 between methods within sites. For the Dominican Republic, 25 and 26 morpho-species were identified in the transects and plots, respectively. There was a 24-31% overlap (69-76% complementarity) between sites. The Sørensen Similarity Coefficient between sites was 0.40-0.47 for transects and plots, respectively, and 0.40-0.70 between methods within sites. The species accumulation curve indicates that the minimum number of subplots needed is 10 per transect and 60-70 per plot to obtain between 70-80% of the species. In terms of sampling effort, I concluded that at least 12 samples distributed throughout a year but with shorter intervals during the rainy season are needed. There was no difference between using transects or plots based on the number of species and similarity indexes. Based on a Chi-Square analysis using the frequencies of species, however, transects were better that plots because the distribution of species is more homogeneous.
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