Height-diameter models for saplings in a spruce-fir mixed forest in Changbai Mountains.

Total tree height (H) and diameter at breast height (D) outside bark are two most essential variables in most forest inventories, but the height curves for saplings have rarely been developed so far. Using the data from 12 permanent 1-ha sample plots investigated in 2013, we found that, among 35 empirical tree height-diameter at breast height model, the cubic polynomial proposed by Curtis in 1967 (h=a0+a1d+a2d2+a3d3) well fit the height-diameter model of saplings of five species in Changbai Mountains, and the coefficient of determination for Pinus koraiensis was the highest (R2=0.786 5). The validation of the models showed that all the models performed well and were quite suitable to the saplings in spruce-fir mixed forest in this area. The analysis of tree height growth for the five species by space substitute time indicated that the height of Acer mono was higher than others, the height growth of Pinus koraiensis and Abies nephrolepis was similar, and the height growth of spruce was low in early stage but increased quickly afterwards.