Frassfall, the amount of solid insect waste falling to the forest floor, has been variously used to study larva populations, defoliation events, and the movement of biomass and nutrients from the canopy to the forest floor. In tropical forests, long term frassfall data may allow us to understand changes in insect abundance and activity with changes in land-use and climate. Here we explore 10 years of frassfall data from secondary seasonally dry tropical forest of Guanacaste, Costa Rica. We collected the contents of 72 0.25 m2 litter traps monthly for 10 years. We positioned 4 litter traps each in 18 forest inventory plots. The contents of the litter traps were dried and sorted into leaves, flowers, fruits, twigs, and frass and weighed. We averaged the frassfall of the 4 litter traps in each plot to calculate a frassfall per unit area. We explored frassfall patterns over time, forest age, and forest subtype.
Results/Conclusions
The grand mean frassfall of all 18 plots over 10 years was 19.3 g m-2 yr-1. The highest frassfall (averaged across all 18 plots) was 33.0 g m-2 yr-1 recorded in 2010 and the lowest was 7.6 g m-2 yr-1 in 2015 (a severe drought year). Each year, high frassfall coincides with the rainy season in Guanacaste. The start of the rainy season, May through August, accounted for 62% of annual frassfall. Lower frassfall (31% of annual) occurred in the late rainy season, September through December, and very little frassfall (7% of annual) occurred the driest months (January through April). Frassfall generally increased in wet years and declined in dry years but there significant variation in frassfall that precipitation does not account for. Inter annual variation appears to be driven by June frassfall, the month when most of the large frassfall events occurred. With several high and low frassfall years at the start and end of our dataset, there is not a clear pattern of increase or decrease in annual frassfall over time. This poster will explore these results further including analyzing how differences in forest age, composition, and biomass might explain variation in frassfall across this heterogeneous landscape.
