[Estimation of leaf area index of three forest types in Xiaoxing'an Mountains of Northeast China].

From early July to early November 2009, the effective leaf area index (LAIe) of secondary Betula platyphylla forest, spruce-fir valley forest, and mixed broadleaved-Korean pine forest in Xiaoxing'an Mountains were measured with Winscanopy2006 Plant Canopy Analyzer, and the LAIe measured in early November and calibrated with the woody-to-total ratio as well as the clumping index (for clumping beyond the shoots) and the needle-to-shoot area ratio (for clumping within the shoots) was derived as the true leaf area index (LAIt). In combining with litterfall method, the LAIt and its seasonal dynamics of the three forest types were estimated. The LAIe of the secondary B. platyphylla forest reached its peak in July, with a value of 2.21, and that of the spruce-fir valley forest and mixed broadleaved-Korean pine forest peaked in August, with the values of 2.57 and 2. 68, respectively. All the three forest types had the highest LAIt in July, with the values of 3.44, 3.86, and 6.93 for the secondary B. platyphylla forest, spruce-fir valley forest, and mixed broad-leaved-Korean pine forest, respectively. In comparison with the method proposed in this study, the peak time LAIe of the secondary B. platyphylla forest, spruce-fir valley forest, and mixed broad-leaved-Korean pine forest obtained by the optical instrument method was underestimated by 33.1%, 32.9% and 66.0%, respectively, and the LAIe of the three forest types in the entire study period was underestimated averagely by -13.2%, 22.8%, and 56.5%, correspondingly.