The influence of epiphyte cover on branch temperature in a tropical tree

The air temperature around three branches loaded with epiphytes in a tropical lowland rain forest in French Guiana was measured from mid-June to mid-July 1997. These data represent the first direct measurements of temperature close to epiphyte-loaded branches in a tropical lowland forest. The epiphytic biomass of one of the branches was removed after two weeks of measurements. These differences in stripped versus unstripped branch temperatures were positive during day time. A maximum difference of 4.8 degreesC was measured on a single sunny day; the maximum of four mid-day hours averaged over all days was 2.3 degreesC. Maxima were determined at locations close to the branch, representing high accumulations of humus, while nearly no differences were detected 75 cm away from the branch. At night, the temperature was cooler after epiphyte biomass removal; differences were up to -0.5 degreesC. Close to the branch, evaporation of stored water in humus cools the environment while latent heat transformation on epiphyte surfaces raises temperature. Shading under a branch prevents heating. Epiphytes reduce air circulation, keeping unheated air on branch undersides. At night, auto-heating of humus may occur through increased rates of respiration.