Leaf Growth and Herbivory Dynamics of Saplings in Tropical Seasonal Rainforest Gaps in Xishuangbanna
ZHENG Zheng, CHEN Xu-Dong, MAO Hong-Wei, ZHENG Quan, YU Fan
Chin J Plan Ecolo. 2001, 25 (6):
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Leaf growth and herbivory dynamics of six tree species saplings were measured in tropical seasonal rainforest gaps in Xishuangbanna, SW China. Leaf growth in all six species mostly occurred in the rainy season (from May to Oct. ) and ceased in the foggy cool period (from Nov. to Feb. ) of the dry season. Saplings of the heliophilous species studied began to sprout in the dry hot period (from March to April) of the dry season, but saplings of the climax species began to sprout at the beginning of rainy season in May. These results indicate that low temperature during the foggy cool period restrained leaf sprouting in both groups while water deficiency during the dry hot period restrained leaf sprouting for climax species. Leafing synchrony, measured as the coefficients of variation (C. V. ) of leaf production in per two months, the 6 species were ranked as follows. Shorea chinensis (1.42), Pseuduvaria indochinensis (1.41), Duabanga grandiflora (1.02), Gmelina arborea (0.98), Anthocephalus chinensis (0. 84), Cassia siamea (0. 84). Peaks of leaf fall for some of the tree species saplings coincided with the dry season while serious herbivory of G. arborea leaves resulted in intensive defoliation of that species during July and August also. Leaf herbivory was strongest in the rainy season. While the leafing of A. chinensis and G. arborea in the dry hot periods may act to reduce herbivory, but for C. siamea, the synchronization of leafing during the time did not appear to affect the rate of leaf damage by herbivores. For these six species saplings, the annual leaf production processes were positively correlated with annual leaf herbivory processes. These correlations reached significance (p <0.05 or p<0.01) for S. chinensis, P. indochinensis, D. grandiflora and A. chinensis. For S. chinensis, P. indochinensis, the synchronization of leafing at the beginning of the rainy season may also act to lighten herbivory impacts. Leaf-eating insects preferred young leaves to mature leaves. On an average, young leaf area eaten accounted for 72.9% of the total leaf herbivory, and the grazing rates (Percentage of leaf area eaten per month) of young leaves was 4.3 times higher than that of mature leaves.