Variation in phenology, growth, and wood anatomy of Toona sinensis and Toona ciliata in relation to different environmental conditions

Tree-ring proxy data from subtropical to tropical Australasia are valuable though rare sources for climate reconstructions. Toona sinensis (A. Juss.) M. Roem. and Toona ciliata M. Roem. occurring naturally in this region are among the most promising tree species for future tree-ring research. However, little is known about their phenological behaviors and the influence of environmental conditions on their intraseasonal growth and wood anatomical properties. Growth experiments were conducted on young trees of both species to investigate their responses to different treatments. The results show that phenology and growth were adjusted according to the severity of the treatments. Restricted growth conditions often caused longer leafless periods, shorter flushes of leaves, and decreased height and diameter growth increments, and they resulted in more but smaller vessels. Under optimum conditions, T. ciliata did not become leafless, had multiple leaf flushes, sustained growth throughout the experiment, and did not form a tree-ring boundary. All other specimens of both species entering leafless or at least semileafless periods formed one tree-ring boundary during the experiment. The growth reaction was more distinct in the latewood than in the earlywood, in extreme cases suppressing the latewood totally. Although the experiment was conducted on young trees and hence should not simply be generalized and applied to adult specimens, the results indicate that both species are well suited for reliable future dendroclimatological investigations. Such studies need to pay attention to possible missing rings in the young parts of tree-ring series.