INFLUENCE OF CROWN CLASS AND SHADE TOLERANCE ON INDIVIDUAL TREE DEVELOPMENT DURING DECIDUOUS FOREST SUCCESSION IN CONNECTICUT, USA

Sixty years of individual tree crown class records were used to elucid ate the influence of crown class (dominant, codominant, intermediate, or suppressed), shade tolerance (intolerant, midtolerant, or tolerant) , and their interactions on the probability of individual tree movemen t among crown classes. Trees were measured at 10 year intervals betwee n 1927 and 1987, excluding 1947, on 364 nominal 0.01 ha plots. A total of 14 154 individual tree records were used in this analysis. The tra nsition rates among crown classes for 30 year intervals (1927-1957 and 1957-1987) were examined for all combinations of antecedent crown cla sses and tolerance rankings. The distribution of ingrowth among tolera nce rankings was also examined. Mortality rates increased with decreas ing crown class for all tolerance rankings, and mortality rates increa sed with decreasing tolerance. Compared with tolerant trees, midtolera nt and intolerant trees had higher rates of ascension into dominant an d codominant crown classes and exhibited higher persistence rates in t he dominant crown class. These factors suggest that midtolerant and in tolerant trees have an advantage over tolerant trees in the higher cro wn classes. In contrast, tolerant trees had the advantage in suppresse d and intermediate crown classes, with lower mortality rates, higher p ersistence, and higher rates of crown class ascension than for midtole rant or intolerant trees. Crown class stratification was driven by the change in relative advantage of each tolerance ranking among the crow n class. Results of this study suggest that the canopy stratum (upper canopy, lower canopy, or mixed) affected by disturbance is as importan t as disturbance scale, intensity, and frequency in influencing the co mposition of the suppressed crown class. Because the suppressed crown class is in a constant state of high flux, with fewer than 30% of the suppressed trees remaining in the suppressed crown class for any 30 ye ar period, a small change in the relative persistence or ascension rat es among tolerance rankings, whether by a different disturbance or cli mate regime, could alter the proportion of tolerance rankings in the s uppressed crown class and ultimately result in an alternative successi on.