PARENT SESSION
Poster Session # 13: Biogeochemistry, Photosynthesis, and Respiration.
Tuesday, August 5 Presentation from 5:00 PM to 6:30 PM. SITCC Exhibit Hall B.
Whether repeated harvest and acid rain threaten calcium supply in northern hardwood forests may depend on apatite weathering.
Yanai, Ruth1, Hamburg, Steven2, Arthur, Mary3, Blum, Joel4, 1 SUNY-ESF, Syracuse, NY2 Brown University, Providence, RI3 U of Kentucky, Lexington, KY4 U of Michigan, Ann Arbor, MI
ABSTRACT- Acid rain and repeated forest harvest are thought to threaten the supply of calcium to forested ecosystems. Ecosystem budgets for New Hampshire northern hardwoods show that young stands (<30 y old) mobilize Ca at rapid rates (3.3 to 4.7 g Ca m-2 y-1), based on the rates of Ca export in streamwater and accumulation in vegetation and the forest floor. In contrast, older stands are in approximate steady state (losing 1 g Ca m-2 y-1). If young stands tap a pool of soil Ca unavailable to older stands, then repeated harvest will not result in rapid Ca depletion, as has been predicted based on rates of export and weathering in older stands. If, on the other hand, rapid Ca uptake by young stands hastens the depletion of readily available pools, sustainable forestry may be threatened. We have identified apatite (Ca phosphate) at depth in soils at the Hubbard Brook Experimental Forest (65 g Ca/m2 in E and B horizons and 6 g Ca/m2 per cm of depth in the C horizon), based on sequential extractions and P:Ca and Ca:Sr ratios. We propose that apatite weathering is accelerated in young stands, perhaps because P is more limiting than N shortly after forest disturbance. We have analyzed soils and plant material from 10 additional sites in New York, Pennsylvania, and Maine to determine the importance of this previously unappreciated Ca source to forests of different ages.
Key words: succession, weathering, calcium, acid rain