Document: STE-3-60-11
Biotic control of calcium decline in forest soils.
HAMBURG, S.P.* 1, R.D.YANAI 2 and M.A.ARTHUR 3
Brown University, Providence, RI, USA 1
SUNY , Syracuse, NY, USA 2
University of Kentucky, Lexington, Kentucky, USA 3
Abstract:
Concern is growing that prolonged exposure to acidic precipitation, along with declining Ca in precipitation, decreases the availability of base cations in forest soils. This concern stems from observations of declining base saturation in the soils of mature forest stands in North America and Europe, the already low base status of most northeastern US soils, and an inability to identify pools of available Ca sufficient to insure long-term forest growth. We suggest that forest succession controls calcium cycling and changes in calcium availability in northern hardwood forests to a greater degree than does acid precipitation. Understanding the relative importance of biotic and abiotic processes to cation biogeochemistry is critical to the effective design of environmental policy. Biotic regulation of Ca cycling is particularly important in regions where historic changes in land-use have resulted in near synchronous aging of forests. When environmental stress and forest succession occur simultaneously, declines in streamwater and soil calcium concentrations could mistakenly be assumed to indicate anthropogenic acidification rather than the effects of land-use change. To determine the importance of successional changes in the northern hardwood forest on calcium availability we measured changes in the following three indicators in stands of different ages: Terrestrial snail mass in 7 sites over 18 years; Ca concentration of leaf litter in 13 sites; and forest floor calcium in the same 13 sites over 15 years. We found that snail abundance, Ca content and Ca concentrations in the forest floor and Ca concentrations in litterfall were all significantly higher in forest stands <35 years old compared with older stands. An input-output model of young forest stands indicates that vegetative uptake of mineral soil calcium suppplies about 7 g-Ca m-2 y-1 to the rest of the ecosystem. This contrasts with older forests (>35 y), where the mineral soil provides negligible net calcium to the ecosystem (1 g-Ca m-2 y-1). These observations support our hypothesis that synchronous aging of previously harvested forests in the northeastern US may be a major contributor to patterns of declining soil and streamwater Ca concentrations.
Keywords: Ca cycling, acid precipitation, forest decline, succession
This abstract is being presented at: 10:30 AM in session:
Oral Session #61: Plant Responses to Nutrients.