Long-term censuses of terrestrial gastropods have been undertaken on the Luquillo Forest Dynamics Plot (LFDP), Puerto Rico, since 1989. These data routinely shown significant variation in the spatial distribution of snail species over this 16-ha area. The role of habitat factors causing this variation has not been fully explored. Historical anthropogenic land use, in particular, is known to produce long-term effects on forest habitat and may impact snail diversity. This study investigated the influence of historic coffee cultivation on modern snail communities. Snail diversity was surveyed in an area neighboring the LFDP that supported coffee cultivation until the 1930’s. Snails were sampled in two consecutive summers along three transects running perpendicular to known plantation boundaries. Each transect consisted of 10 plots (3 m radius x 3 m height) with 5 plots in the historical plantation and 5 plots in adjacent uncultivated forest. Surveys were conducted at night to coincide with peak snail activity. Each plot was sampled once for a minimum of 30 man-minutes during which time all emergent snails were tallied on all available substrates.
Results/Conclusions
Caracolus caracolla and Nenia tridens were the most common snails in both land uses. These species, however, were 3.3x and 2.5x more abundant on old coffee. Coffee C. caracolla populations also supported numerous juveniles, while all individuals sampled on uncultivated forest were large adults. Platysuccinea portoricensis was also abundant on old coffee, but scarce on uncultivated forest. Additionally, Shannon diversity was higher on the coffee plantation (1.10 vs. 0.74). Differences in habitat, as influenced by land-use history, may underlie these observed differences. Previous surveys of these transects found distinct differences in tree species composition and soil properties between land uses. Notably, calcium, nitrogen, and pH were all elevated in old coffee soils. Limestone, applied to coffee fields to raise pH, is still present is high concentration. Calcium is needed by snails for shell growth, so limestone soil amendments would benefit resident snails. Higher soil pH would accelerate litter decomposition and increase available food for detrivorous snails. Elevated soil nitrogen likely arose from leguminous Inga vera trees planted to shade coffee plants. The resulting increase in soil fertility would promote faster forest growth and greater litterfall production. These increased detrital inputs coupled with faster decomposition would act to enhance snail habitat.
