Estimation Of Leaf Area Index Of Three Forest Types In Xiaoxing’an Mountains

Leaf area index (LAI) is an important variable in the study of forest ecosystem processes, but very few studies are designed to monitor LAI and the seasonal variability in a mixed forest using non-destructive sampling. In this study, first, true LAI from May1st and November15th was estimated by making several calibrations to LAI as measured from the WinSCANOPY2006Plant Canopy Analyzer in2007. These calibrations include a foliage element (shoot, that is considered to be a collection of needles) clumping index (for clumping beyond the shoots) measured directly from the optical instrument, TRAC (Tracing Radiation and Architecture of Canopies); a needle-to-shoot area ratio (for clumping within the shoots) obtained from shoot samples; and a woody-to-total area ratio. Second, by periodically combining true LAI (May1st) with the seasonality of LAI for deciduous and coniferous species throughout the leaf-expansion season (from May to July), we estimated LAI of each investigation period in the leaf-expansion season. Third, by combining true LAI (November15th) with litter trap data (both deciduous and coniferous species), we estimated LAI of each investigation period during the leaf-fall season (from July to November). Finally, LAI for the entire canopy then was derived from the initial leaf expansion to the leaf fall. And using the two methods, we studied the seasonality of Leaf area index of three typical forest types in Xiaoxing’an Mountains:secondary Betula platyphylla forest, Spruce-fir valley forest and mixed broadleaved-Korean pine forest in the leaf-fall season in2009.The results showed that:first, for mixed broadleaved-Korean pine forest in2007, LAI reached its peak with a value of6.53m2m-2(a corresponding value of3.83m2m-2from optical instrument) in early August, and the mean LAI was4.97m2m-2from May to November using the proposed method. The optical instrument method underestimated LAI by an average of41.64%(SD=6.54) throughout the whole study period compared to that estimated by the proposed method. Second, the LAI。 of secondary B. platyphylla forest reached its peak with a value of2.21in July, while the peak of LAIe was noticed in August for both Spruce-fir valley forest and mixed broadleaved-Korean pine forest with values of2.57and2.68, respectively. The highest LAI for all three forest types was obtained in July with values of3.44,3.86, and6.93, respectively. In comparison with the method proposed in this study, the LAIe obtained from the optical instrument method were underestimated by33.09%,32.93%, and65.97%, respectively; For Spruce-fir valley forest and mixed broadleaved-Korean pine forest, the optical instrument method underestimated the LAI by22.80%and56.47%on average; however, it was overestimated by13.17%for secondary B. platyphylla forest during the falling period. The result of the present work implied that our method would be suitable for measuring LAI, for detecting the seasonality of LAI in a mixed forest, and for measuring LAI seasonality for each species; and the LAI and its seasonal dynamics obtained from the comparative analysis of two methods would provide a reference for accurate estimation of LAI.