Recovery of net primary production in subalpine meadows of Mount St. Helens following the 1980 eruption

Abstract

The deposition of 5–10 cm of tephra from the 1980 eruption of Mount St. Helens had no more effect than subsequent yearly weather fluctuations on the net primary production of subalpine meadows. The net primary production of areas subject to cold mudflows slowly increased as surviving plants resprouted through the eroded surface and has remained below that of tephra deposition areas. The net primary production of tephra deposition areas fluctuated dramatically (coefficient of variation = 40%) in the seven summers following the eruption. An inverse relationship between net primary production and nutrient concentration of individual species contributed to stability in aboveground nutrient pools from year to year. The dominant community members responded similarly to differences among years in summer precipitation, with little evidence of compensatory growth that would help stabilize community production. Tephra greatly inhibited seedling establishment. Species density (number of species per square metre) and diversity (H′) declined in a community having species that rely on sexual reproduction for persistence and also in experimental tephra addition plots in a more species-rich community. These results indicate that although the short-term effect of tephra deposition on net primary production was minor, the long-term consequence will be of community simplification, which will contribute to fluctuation in net primary production in response to yearly weather patterns.