The Ecohydrological Effects of Reducing Throughfall and Fog Inputs in a Tropical Cloud Forest

Mean cloud altitudes are expected to increase over the coming century, which along with warming may increase the frequency of water stress in tropical montane cloud forests, where soils are often shallow and precipitation is highly seasonal.

In a unique paired experiment at the Wayqecha Cloud Forest Biological Station in Peru (3000 m elevation), we reduced fog inputs to one plot by >90% using a 30-meter high curtain, while in another plot we excluded >90% of throughfall. After more than one year of these treatments, we found that sapflow and tree growth were drastically reduced during both the rainy and the dry seasons in the throughfall exclusion plot, while the absence of substantial mortality or dieback after more than a year of this extreme experiment suggests the importance of fog interception to the survival of drought-stressed trees. The effects of excluding fog inputs alone were more subtle, with no significant reduction in either sapflow or stem growth. This may point to the sufficiency of the current precipitation regime for maintaining ecosystem function in this cloud forest ecosystem, at least over the short term.