Tree-ring width and δ¹³C records of industrial stress and recovery in Pennsylvania and New Jersey forests: Implications for CO₂ uptake by temperate forests

We present dendrochronological records of tree-ring width and δ¹³C values for representative living trees (ages of 70 to 230years) in Pennsylvania and New Jersey to investigate the ecological responses to industrial pollution and recent management and their effects on carbon storage in the temperate forests. Chestnut oak, red oak and cedar trees consistently show elevated δ¹³C levels (1.3 to 4.1‰ higher than unpolluted normal values) during the period of intense pollution from ~1900 to ~1970, indicating significant industrially induced physiological stress on the trees. Since ~1970, oak and cedar trees have shown remarkable increase in growth rates and rapid decrease of 0.6 to 2.5‰ in δ¹³C values, indicating the recovery of trees corresponding to the implementation of the Clean Air Act in the early 1970s. The growth enhancement since 1970 has resulted in an increase in biomass of ~26% in cedar trees and ~66% in oak trees, suggesting that air-cleaning efforts have made a significant contribution to CO₂ uptake by the temperate forests, at least in the northeastern USA.