Potential variables forcing litterfall in a lower montane evergreen forest using Granger and superposed epoch analyses

The interplay between long-term environmental variability and litterfall is complex and through this study, we quantified the response of peak leaf, flower, and fruit litterfall production to such variability in a lower montane evergreen forest located in Doi Suthep-Pui National Park, Thailand. We observed seasonality in litterfall accumulation with peak leaf and flower litterfalls occurring mostly during the cool and hot dry seasons, while fruit litterfall occurs mostly during the wet season. Probable associations with environmental drivers (barometric pressure, temperature, relative humidity, number of sunlight hours, evaporation, wind speed, and vapor pressure deficit) were tested on a 5-year litter trap dataset using superposed epoch analysis and Granger causality tests. The tests indicated that significant deviations in barometric pressure, maximum temperature, maximum relative humidity, and wind speed were the most plausible precursors to peak litter production of all components. Additionally, we observed a lag in peak litterfall production relative to climate variability by up to 4 months for most of the climate variables. Changing environmental conditions can affect both the timing and amount of litterfall production, which in turn can alter the nutrient recycling rate and other essential ecosystem services of such forests.