Tree height and tropical forest biomass estimation

[摘要] Tropical forests account for approximately half of above-ground carbonstored in global vegetation. However, uncertainties in tropical forestcarbon stocks remain high because it is costly and laborious to quantifystanding carbon stocks. Carbon stocks of tropical forests are determinedusing allometric relations between tree stem diameter and height andbiomass. Previous work has shown that the inclusion of height in biomassallometries, compared to the sole use of diameter, significantly improvesbiomass estimation accuracy. Here, we evaluate the effect of heightmeasurement error on biomass estimation and we evaluate the accuracy ofrecently published diameter–height allometries at four areas within theBrazilian Amazon. As no destructive sample of biomass was available at thesesites, reference biomass values were based on allometries. We found that theprecision of individual tree height measurements ranged from 3 to 20% oftotal height. This imprecision resulted in a 5–6% uncertainty in biomasswhen scaled to 1 ha transects. Individual height measurement may be replacedwith existing regional and global height allometries. However, we recommendcaution when applying these relations. At Tapajos National Forest in theBrazilian state of Pará, using the pantropical and regional allometricrelations for height resulted in site biomass 21% and 25% less thanreference values. At the other three study sites, the pantropical equationresulted in errors of less that 2%, and the regional allometry producederrors of less than 12%. As an alternative to measuring all tree heightsor to using regional and pantropical relations, we recommend measuringheight for a well-distributed sample of about 100 trees per site. Followingthis methodology, 95% confidence intervals of transect biomass wereconstrained to within 4.5% on average when compared to reference values.

[学科分类] 地球化学与岩石