The phytomass of tree species is generally estimated using the allometric relationship. Stem diameter at breast height DBH is one of the most popular size index for estimating the phytomass. Although the measurement of DBH is practically convenient, DBH seems to be a bit lacking in biological meaning. Especially, the use of DBH involves some fundamental limitation in studying allometry of tree species since it is impossible to measure DBH for trees being shorter than breast height. The tree individual changes its shape according to its growth since the environmental conditions change drastically depending on its size. Although several past studies applied the stem diameter at relative tree height for evaluating allometry to estimate tree phytomass, there was no study aimed at all age levels from seedlings to mature trees.

In the present study, the relationship of phytomass to DBH and stem diameter at 10% of tree height was investigated on the basis of a data set obtained from a tropical rainforest at Sao Gabriel da Cachoeira, Brazil. The phytomass including roots was measured for 160 trees from seedlings to mature trees. The size dependence of the relationship between phytomass and stem diameter will be discussed.