Large Rainfall Pulses Control Litter Decomposition in a Tropical Dry Forest: Evidence from an 8-Year Study

We investigated the influence of rainfall attributes on litter decomposition over an 8-year period in a well-preserved tropical dry forest ecosystem in western Mexico. We examined the relationship between the size and number of rainfall events and rainy-season litter decomposition rates and determined if this relationship varied along a landscape gradient. A mass balance approach was used to estimate decomposition rate in four permanent 2,400 m(2) plots located in two small watersheds. Watershed I included three plots in different landscape positions (upper, middle, and lower) in the elevation gradient, whereas Watershed IV included one plot in the middle position. Surface litter C mass was lower in the rainy than in the dry season in all plots in response to seasonal fluctuations in rainfall. The frequency of small (<= 5 mm) and medium (5.1-9.9 mm) size rainfall events largely did not correlate with litter decomposition, but the frequency of large events (>= 10 mm) had a positive correlation with decomposition rates ( < 0.05), except in plot IV ( < 0.1). Decomposition rates were similar among plots at the different landscape positions within Watershed I ( > 0.05). The relevance of large rainfall events (>= 10 mm) in rainy-season litter decomposition suggests that changes in the precipitation regime which alter the frequency of these rainfall pulses or increase their variability would affect the vulnerability of the litter C and nutrient pools to extreme events.