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 lenta L.) >1.5 cm have been monitored at 10-year intervals since 1927. Survival and development of black birch in 25- to 85-year-old stands was influenced by antecedent crown class, sprout rank, and disturbance. Mortality was typically higher for trees in the lower than upper crown classes. Black birch demonstrated high flux among crown classes. Persistence in the upper canopy was 70 years for dominant trees and only 20 years for codominant trees. Trees in lower crown classes generally ascended into higher crown classes at a faster rate than did trees in higher crown classes. Survival in stands from ages 25 through 55 years was higher for the largest stem in a sprout clump than for lesser sprouts and trees that had never been part of a sprout clump. Survival was independent of diameter class when crown-class effects were removed. Immediate response of black birch to a period of upper canopy disturbance caused by drought and severe defoliation included temporary decreases of crown-class regression and mortality rates, and a concomitant temporary increase of crown-class persistence rates. Crown-class ascension rates increased after a 10-year lag for codominant and intermediate trees, and a 20-year lag for suppressed trees. Black birch ingrowth also responded positively to upper canopy disturbance. The increased use of partial cutting, i.e., anthropogenic upper canopy disturbance, in the northeastern United States is creating conditions advantageous for black birch development.