ASSESSMENT OF SOIL CALCIUM STATUS IN RED SPRUCE FORESTS IN THE NORTHEASTERN UNITED-STATES

Long-term changes in concentrations of available Ca in soils of red sp ruce forests have been documented, but remaining questions about the m agnitude and regional extent of these changes have precluded an assess ment of the current and future status of soil Ca. To address this prob lem, soil samples were collected in 1992-93 from 12 sites in New York, Vermont, New Hampshire, and Maine to provide additional data necessar y to synthesize all available research results on soil Ca in red spruc e forests. Sites were chosen to encompass the range of environmental c onditions experienced by red spruce. Concentrations of exchangeable Ca ranged from 2.13 to 21.6 cmol(c) kg(-1) in the Oa horizon, and from 0 .11 to 0.68 cmol(c) kg(-1) in the upper 10 cm of the B horizon. These measurements expanded the range of exchangeable Ca reported in the lit erature for both horizons in northeastern red spruce forests. Exchange able Ca was the largest Ca fraction in the forest floor at most sites (92% of acid-extractable Ca), but mineral Ca was the largest fraction at the three sites that also had the highest mineral-matter concentrat ions. The primary factor causing variability in Ca concentrations amon g sites was the mineralogy of parent material, but exchangeable concen trations in the B horizon of all sites were probably reduced by acidic deposition. Because the majority of Ca in the forest floor is in a re adily leachable form, and Ca inputs to the forest floor from the miner al soil and atmospheric deposition have been decreasing in recent deca des, the previously documented decreases in Ca concentrations in the f orest floor over previous decades may extend into the future.