Lifetime growth patterns and ages of Bolivian rain forest trees obtained by tree ring analysis

Growth patterns and ages of tropical forest trees are strongly governed by temporal variation in light availability. Periods of high growth after canopy disturbances (releases) are necessary for successful canopy regeneration, but their importance cannot be studied without lifetime data. The recent detection of annual rings in tropical forest trees enables such analyses. We used tree ring analysis to study lifetime growth patterns and age variation in six Bolivian rain forest species. Our aims were to evaluate the magnitude and sources of age variation of canopy trees, to analyse the frequency of suppression and release events, and to analyse the relation between temporal growth changes and tree age. The average age of trees of 60 cm diameter differed threefold between species and by two- to threefold even within species. This variation was mainly explained by variation in passage time through the juvenile categories. We used strong relative growth changes to detect release and suppression events. On average, canopy trees experienced 0.8-1.4 releases, with a maximum of 4. We distinguished four canopy accession patterns by which trees have attained the canopy (growth without major growth changes, one release event, one suppression event, or several release and suppression events), with increasing time required to attain the canopy. The distribution of trees over categories of canopy accession is therefore closely related to the average age of canopy trees and its variation. There were clear differences among species in how trees attained the canopy and in the length of slow-growth periods they experienced, suggesting differences in shade tolerance and growth responses to gaps, which are indicative of life-history differences among non-pioneer tree species. Canopy attainment of tropical rain forest trees does not occur by steady growth, but rather by irregular patterns of growth spurts and stand-stills, probably mostly caused by temporal variation in light. Differences in these patterns may largely explain differences in the ages of large tropical rain forest trees.