CLOUD DEPOSITION TO A SPRUCE FOREST EDGE

Deposition from clouds to a spruce (Picea rubens Sarg.) forest edge on Hunter Mt. in the Catskill Mts of New York State was measured during 1987 and 1988 to determine whether the windward edge of forest floor receives greater deposition of water and ions via cloud water than the interior of a forest. Throughfall was used as a measure of deposition and was collected during cloud-only and mixed cloud-and-rain events along five windward-to-leeward transects in a 30 x 30 m forested area. Ambient cloud water was also collected in a passive collector and chemically analyzed. Trees at the edge of the forest received on average three times, and up to 15 times, greater deposition of ions than those in the interior of the forest. Lead content in samples from Hunter Mt. forest floor at the windward edge, relative to the interior, was enhanced as well. Using a regression of distance vs deposition, the deposition ''half-distance'', (i.e. the point at which the rate of cloud water deposition is 50% of the rate at the windward edge of the forest) was found to be 28 m. The cloud deposition data from this study are compared to other studies of Na particle deposition to low-elevation forest edges, which show similar deposition ''half distances'', ranging from approximately 2 to 36 m into the forest. Most models of cloud deposition currently in use assume landscape homogeneity. Montane forest landscapes, however, are often highly heterogeneous, consisting of many ''edges'', and thus current models may seriously underestimate cloud deposition.