Litterfall in forest ecosystems is a major source of carbon and nutrient elements to soils and serves as an index of primary productivity. Despite these important roles, few studies have examined long-term trends in litter production and nutrient inputs. Previous research in hurricane-prone regions indicates a significant effect of hurricanes on litterfall, and in Puerto Rico, a lesser effect of drought, with both disturbances showing positive effects on litterfall inputs as their intensity increases. Previous research has also shown that litterfall recovery from the most damaging hurricane in Puerto Rico in recent history, Hurricane Hugo in 1989, was incomplete after five years. Here we present a 26 year history (1989-2015) of litterfall production and nitrogen inputs to a moist subtropical forest in Puerto Rico. Forest litter was collected bi-weekly from 60 litterfall traps located in the Bisley Experimental Watersheds, within the Luquillo Experimental Forest (US Forest Service). Litter was separated into leaves, woody material, fruits and flowers together, and miscellaneous categories. Samples were analyzed for a suite of nutrient elements; only N inputs are presented here.
Major peaks in litter production and associated N inputs over the 26 years corresponded to the occurrence of hurricanes and tropical storms. Overall, leaves contributed the most to litter production and N input, followed by wood and fruits and flowers. Storm associated litter inputs were dominated by leaves and wood; fruit and flower inputs appeared less affected by these events. Secondary peaks in litter production and N inputs occured in early summer, typically in early June, after the start of the rainy season. Trends in the data suggest leaf litter production stabilized roughly 10 years after Hurricane Hugo (even with other storm disturbances), while wood and fruit and flower inputs stabilized perhaps after 20 years. The chronology suggests recovery from a major hurricane can take longer than previously anticipated and may mask more subtle effects due to changes in climate.