Topographic position effects on growth depression of California Sierra Nevada pines during the 1982-83 El Nino

The El Nino-Southern Oscillation event of 1982-83 was associat with severe winter weather in California, including increased snow accumulations in the Sierra Nevada relative to 1984. The ratio of 1983 needle length to 1984 needle length in 2 species of pine growing near timberline in the Sierra Nevada was examined for evidence of growth depression during the El Nino year. Trees of both Pinus albicaulis (whitebark pine) and P. contorta var. murrayana (lodgepole pine) were sampled from a meadow on the valley floor, N- and S-facing slopes, and at high elevation near treeline. In all cases, average needle length in 1983 was less than that in 1984. Degree of growth depression varied among topographic positions and between species. Whitebark pines displayed greater variation in sensitivity to climatic change. Differences in sensitivity between species were associated with habitat restrictions, eg whitebark pines at high elevations were least affected by the El Nino year, while lodgepole pines were most affected when growing at high elevations. Observed variation in growth depression among topographic positions is probably due to both differences in the length of the 1983 growth season associated with timing of snowmelt and decreased temperatures during the 1983 growing season. -from Authors