Canopy litterfall and soil respiration under rainfall and fog reduction in tropical montane cloud forests

Abstract. Tropical montane cloud forests (TMCFs) are globally important ecosystems that act as large carbon sinks. However, climate-driven declines in rainfall and cloud immersion threaten these forests, and their responses to declines in these distinct water sources remain poorly understood. Two separate large-scale experiments to reduce throughfall (TE) and fog (FE) in a Peruvian TMCF were conducted, to compare the temporal patterns and drivers of canopy litterfall and soil respiration, with nearby control (CON) plots.

Litterfall and soil respiration declined during the relatively dry season on the CON plots. Seasonal patterns of soil respiration were related to soil moisture, while litterfall was related to air temperature. Litterfall and soil respiration on the TE plot were suppressed overall and aseasonal, although litterfall pattern was offset FE-induced increases in litterfall from fine wood structures and epiphytes. On the FE plot, the only sign of altered seasonality was elevated litterfall from reproductive structures in the late dry season relative to the CON plot. There was little consistent interannual trend in either litterfall or respiration over time under the FE treatment. By contrast, the TE treatment was associated with a consistent decline in total litterfall, mainly caused by leaf litterfall while soil respiration initially declined for the first four years of the treatment followed by a rise likely associated with a concomitant increase in soil moisture. TE and FE appear to alter the amount and seasonality of reproductive activity in the canopy which could have major consequences for stand structure in a drier future climate.