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 season soil water potential, and basal area growth were studied in a mature, white pine (Pinus strobus) stand at the Coweeta Hydrologic Laboratory, in western North Carolina. In 1992, four bole-wood cores that spanned the years from 1980 to 1989 were extracted from each of ten equal-size, co-dominant white pine trees within the stand. The 1980s were a time of extreme climate with some of the hottest, driest, and wettest years 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 measured to a depth of 60 cm. After correcting annual wood tissue delta(13)C for atmospheric changes in delta(13)C, carbon isotopic discrimination (Delta) ranged from 18.52 to 19.62 parts per thousand. The Delta of annual wood tissue was positively correlated with average growing season soil water potential (r(2) = 0.74, P = 0.0005, n = 10 growing seasons) and average annual basal area growth (r(2) = 0.78, P = 0.0002, n = 10 seasons). Basal area growth and growing season soil water potential 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 basal area growth in mature forest ecosystems.