Publication

This study characterizes the microclimate and soilwater conditions of three gaps within mixed-dipterocarp rainforest of southwest Sri Lanka. The gaps were each of a different size and within a particular part of the forest topography. The largest pp was in a valley and the smallest on a ridge. Soil water, light quantity, and temperature were recorded within demarcated zones across each gap. Although trends between gaps and within gaps are relatively easily explained, the numerical values reported give a good impression of differences and amplitudes concerned as well as of the actual values in the rainforest understory. Surface soilwater measurements revealed that the ridge gap was more prone to water stress than the valley and midslope gaps. Gap centers of all three disturbances appeared to have lower amounts of surface soil water than adjacent forest understories. Light quantities on a sunny day in the forest understory were between 0.26 and 0.92 mols, of which sunflecks contributed between 24 and 62%. These understory light levels are approximately 1% of full sun exposure. The central zone of the valley pp had the longest duration of full sun (17-54% of the daily photosynthetic photon flux density (PPFD) of full sun). The center of the midslope pp had between 12 and 22% and the ridge had between 7 and 16% of daily PPFD of full sun. Diurnal temperature ranges in pp centers are wider than in adjacent forest understories. Sunny days had the greatest ranges of difference with a maximum of 34-degrees-C on the soil surface of the valley gap center, while surface temperatures in the understory did not exceed 25-degrees-C.