Seasonal Dynamics Of Leaf Area Index Using Different Methods In The Korean Pine Plantation

Leaf area index (LAI), defined as half the total leaf area per unit ground surface area, and is one of the most important characteristics of the plant canopy structure. LAI controls the flux of carbon, solar energy, and water in forest ecosystems. Thus, accurately estimating LAI is essential for simulating the forest process. Furthermore, the seasonality of LAI estimation is of particular interest. Methods directly estimating LAI mainly include destructive sampling, allometry, and litterfall. The results of these methods are assumed to provide values close to the true LAI. However, the first two methods destroy the samples, as well as labor intensive. By contrast, the litterfall method is the best choice in obtaining accurate LAI. At present, the optical method has been widely used to estimate LAI because of its convenience and speed. However, the accuracy of optically measured LAI needs to be verified. This verification is performed because the indirect method often underestimates LAI. In the present study, allometry method (including two different allometry equations, namely, A and B), litterfall method, combinational method (the LAI derived from optical method were calibrated by taking into consideration the woody-to-total ratio (α), as well as the clumping index, and combining the litterfall method), and optical method were used to estimate LAI in the Korean pine (Pinus koraiensis) plantation in Xiaoxing’an Mountains. First, we estimated the effective leaf area index (Le) and its seasonality in the Korean pine plantation using optical method (hemispherical photography). To obtain accurate LAI, we estimated the LAI seasonal dynamics by combining litterfall method, combinational method, and allometry methods in accordance with the leaf seasonality observation from May to August. Subsequently, we compared the results obtained from the different methods. The results showed that P. koraiensis leaf stopped growing in early August, which was approximately two weeks later than the other tree species. The major species had different leaf fall pattern in the Korean pine plantation. P. koraiensis had two rapidly decreasing flush. The first flush was in June. The second was in late September. However, other species had single rapidly decreasing flush in late September. The LAI seasonal dynamic derived from different methods all show a uni-modal pattern with a peak in early August, with the following order:Allometry-B method (10.58)> Litterfall method (7.90)> Allometry-A method (6.70)> Combinational method (4.41)> Optical method (1.81). In the entire study period (from May to November), the LAI derived from optical method underestimated LAI by an average of81.69%,75.50%,70.18%, and48.90%, respectively, which were in contrast with contrast Allometry-B method, Litterfall method, Allometry-A method, and Combinational method. In the present study, we investigated a practical method for estimating LAI in the Korean pine plantation using a non- destructive method. Furthermore, we compared the difference between the different methods. In addition, this study lays a foundation for the valid LAI estimation of evergreen conifer forest in subsequent studies.