Abstract: Identifying the response characteristics of tree shape structure to heterogeneous habitats can help understand the adaptability of trees to their habitats and the factors determining their growth strategies. Based on the analysis of meteorological, topographic and edaphic factors in Yuanjiang and Mengla, together with under-branch height, tree height, diameter at the breast height, crown diameter, crown ratio and primary branch number of Bombax ceiba L., we quantified the changes of Bombax ceiba tree shape structure in response to environmental factors in different habitats (hot dry valley vs. tropical rain forest). The results showed that tree shape structure of Bombax ceiba was different between Yuanjiang and Mengla. The under-branch height, tree height, diameter at breast height, and crown diameter of Bombax ceiba were greater, while the primary branch number and crown ratio were smaller in Mengla than those in Yuanjiang. The main environmental factors influencing tree shape structure at the two sites were different. Tree shape structure of Bombax ceiba in the Yuanjiang was mainly affected by annual mean maximum temperature (37.8%), slope direction (7.2%), mean vapor pressure (5.2%), average sunshine hours (6.8%), mean annual precipitation (7.0%), total phosphorus content (3.6%), and nitrate nitrogen content (2.6%). By contrast, tree shape structure of Bombax ceiba in the Mengla was mainly affected by average annual temperature (63.5%), nitratenitrogen content (8.9%), total phosphorus content (3.1%), total nitrogen content (2.4%), ammonium-nitrogen content (2.2%), annual mean minimum temperature (1.8%), available phosphorus content (1.7%), and average relative humidity (1.8%). Meteorological, topographical and edaphic factors were the important environmental factors affecting the growth of Bombax ceiba, although their relative importance can vary. Environmental factors explained 81.9% and 87.2% of the variation of Bombax ceiba tree shape structure in Yuanjiang and Mengla, respectively. Tree shape structure of Bombax ceiba in Mengla was more affected by soil nutrients. Collectively, tree shape structure of Bombax ceiba can adapt to the two extreme habitats by the plasticity of functional traits. Our results can provide scientific reference for exploring the relationship between tree shape structure and heterogeneous habitats.

Key words: Bombax ceiba L., plant functional trait, environmental factor, redundancy analysis.