WOOD DELTA-C-13 AS A MEASURE OF ANNUAL BASAL AREA GROWTH AND SOIL-WATER STRESS IN A PINUS-STROBUS FOREST

The relationships between annual wood tissue delta(13)C, growing seaso n soil water potential, and basal area growth were studied in a mature , white pine (Pinus strobus) stand at the Coweeta Hydrologic Laborator y, in western North Carolina. In 1992, four bole-wood cores that spann ed the years from 1980 to 1989 were extracted from each of ten equal-s ize, co-dominant white pine trees within the stand. The 1980s were a t ime of extreme climate with some of the hottest, driest, and wettest y ears recorded at Coweeta. Annual basal area growth ranged from 14.5 to 25.0 cm(2) . tree(-1). yr(-1), and modeled values of average growing season soil water potential ranged from -0.21 to -5.58 MPa, when measu red to a depth of 60 cm. After correcting annual wood tissue delta(13) C for atmospheric changes in delta(13)C, carbon isotopic discriminatio n (Delta) ranged from 18.52 to 19.62 parts per thousand. The Delta of annual wood tissue was positively correlated with average growing seas on soil water potential (r(2) = 0.74, P = 0.0005, n = 10 growing seaso ns) and average annual basal area growth (r(2) = 0.78, P = 0.0002, n = 10 seasons). Basal area growth and growing season soil water potentia l were also correlated (r(2) = 0.64, P = 0.002, n = 10 seasons). These results suggest that annual wood tissue delta(13)C could potentially be useful in estimating historic changes in soil water potential and b asal area growth in mature forest ecosystems.