METHOD COMPARISON ON ABOVEGROUND BIOMASS INVESTIGATION IN A PINUS KESIYA VAR. LANGBIANENSIS NATURAL FOREST BASED ON A CLEAR-CUT PLOT

To obtain suitable methods for accurately investigating the stand aboveground biomass (AGB) and determining plot size for biomass measurement, the plot-size gradient was set to 100 m 2 , 400 m 2 , 600 m 2 , 900 m 2 , and 1500 m 2 in the 0.3 hm 2 clear-cut plot of Pinus kesiya var.langbianensis natural forest of Mojiang county, Pu`er City, Yunnan Province, China.The AGB of each tree in the plot was investigated by a destructive investigation method.The AGB in the different plot sizes was calculated using the biomass model (BM), the biomass-volume regression (BV), the average standard tree of the diameter classes (SDC), the average standard tree of the tree classification (STC), the average standard tree of the stand (STS) and the measurement method (MD).Then, the error differences between these estimation methods were compared with the different plot sizes.The results showed that 1) with the increase in sample size, the mean absolute relative errors (MAREs) of all the methods tended to decrease, and the error values were stable if the plot size was greater than or equal to 400 m 2 .Thus, the plot size for a forest biomass survey should not be less than 400 m 2 .2) BM, BV, and SDC had a lower mean error (ME) and MARE values.Especially, compared to those of the observed data for the 0.3 hm 2 sample plots where the MAREs of the BM and BV were less than 15%, and the MARE of SDC was approximately 15% for wood and total AGB, but higher than 20% for the other three components.Therefore, the BM and BV should be used to estimate stand AGB if reliable biomass models or biomass-volume functions are available, the SDC is recommended for measuring AGB without biomass models, and the STS could be used for wood biomass and total AGB.