INFLUENCE OF CROWN CLASS ON SURVIVAL AND DEVELOPMENT OF BETULA-LENTA IN CONNECTICUT, USA

Crown class, diameter, and sprout rank of 2219 black birch (Betula len ta L.) >1.5 cm have been monitored at 10-year intervals since 1927. Su rvival and development of black birch in 25- to 85-year-old stands was influenced by antecedent crown class, sprout rank, and disturbance. M ortality was typically higher for trees in the lower than upper crown classes. Black birch demonstrated high flux among crown classes. Persi stence in the upper canopy was 70 years for dominant trees and only 20 years for codominant trees. Trees in lower crown classes generally as cended into higher crown classes at a faster rate than did trees in hi gher crown classes. Survival in stands from ages 25 through 55 years w as higher for the largest stem in a sprout clump than for lesser sprou ts and trees that had never been part of a sprout clump. Survival was independent of diameter class when crown-class effects were removed. I mmediate response of black birch to a period of upper canopy disturban ce caused by drought and severe defoliation included temporary decreas es of crown-class regression and mortality rates, and a concomitant te mporary increase of crown-class persistence rates. Crown-class ascensi on rates increased after a 10-year lag for codominant and intermediate trees, and a 20-year lag for suppressed trees. Black birch ingrowth a lso responded positively to upper canopy disturbance. The increased us e of partial cutting, i.e., anthropogenic upper canopy disturbance, in the northeastern United States is creating conditions advantageous fo r black birch development.