Impacts of acidic deposition on high-elevation spruce-fir forests: results from the Spruce-Fir Research Cooperative

Abstract

Large numbers of standing dead red spruce trees in high-elevation spruce-fir forests of the northeastern US, coupled with nearly synchronous decreases in radial growth, have caused much concern and have been linked with elevated levels of air pollutants. These high-elevation forests, frequently immersed in clouds, receive a significant amount of sulfate and nitrate from cloudwater deposition. The Spruce-Fir Research Cooperative, (SFRC), an integrated multi-institutional research program, is investigating a number of hypothesized effects of acidic deposition on the spruce-fir forests including: (1) soil-mediated effects: (2) altered physiological processes: (3) increased foliar injury: (4) increased susceptibility to winter injury. Major conclusions of the SFRC research will be presented in this paper. In the northeastern US, spruce-fir forests are experiencing visible decline, with large numbers of standing dead trees (> 50% on some mountains). Results from a number of research projects suggest red spruce is particularly sensitive to winter injury, that cloudwater inputs increase that susceptibility, and that repeated winter injury may play a role in red spruce decline in the northeastern US. Increased rates of dark respiration, reduced photosynthesis, and reduced foliar chlorophyll levels have been measured for red spruce at sites receiving high cloudwater deposition in the southern Appalachians relative to trees receiving lower deposition, and these physiological changes may be contributing to reduced growth of red spruce saplings. Effects of acid anion deposition on soil aluminum levels could have important implications for soil and tissue cation levels. The relative role of the particular mechanisms associated with acidic deposition may vary with natural biotic and abiotic factors.