Topographic Position Effects on Growth Depression of California Sierra Nevada Pines During the 1982–83 El Niño

Abstract

The El Niño-Southern Oscillation event of 1982-83 was associated with severe winter weather in California, including increased snow accumulations in the Sierra Nevada relative to 1984. We examined the ratio of 1983 needle length to 1984 needle length in two speces of pines growing near timberline in the Sierra Nevada for evidence of growth depression during the El Niño year. Trees of both Pinus albicaulis (whitebark pine) and P. contorta var. murrayana (lodgepole pine) were sampled from four topographic positions at the study site: a meadow on the valley floor, north- and south-facing slopes, and at high elevation near treeline.

In all cases, average needle length in 1983 was less than that in 1984. The degree of growth depression varied among topographic positions and between species. Whitebark pines displayed the greatest variation in sensitivity to climatic change. Differences in sensitivity between species were associated with habitat restrictions; e.g., whitebark pines at high elevations were least affected by the El Niño year, while lodgepole pines were most affected when growing at high elevations. It is hypothesized that observed variation in growth depression among topographic positions is 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.