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Estimation of above ground biomass of forest trees using dbh as a single parameter
By hiran | December 10, 2007
I D Welivita and S M C U P Subasinghe
Department of Forestry and Environmental Science,
University of Sri Jayewardenepura, Sri Lanka
Forests in Sri Lanka contribute to the mitigation of climate change through sequestrating a net amount of carbon dioxide and also maintaining carbon stock as biomass. Total tree biomass comprised of above ground and below ground biomass of trees. This paper presents a methodology developed to estimate individual tree above ground biomass using allometric relationships. The advantage of this method is that the above ground biomass per unit area can be determined by estimating these values for different species separately within that area. The present study was conducted in Yagirala Natural Forest Reserve situated in Kalutara District, low country wet zone of Sri Lanka. In this study, the above ground biomass of different species available in that forest were predicted using the diameter at breast height (dbh).
45 tree species were identified in the forest and models were separately developed for each species. For each species, 3 classes were established using the size, i.e., small, medium, and large. For class 1 and 2 trees, the main stem and the average size branch were divided into sections and for each section end diameters and length were measured. The volume of each section was estimated using Smalian’s formula. The total branch volume was estimated by multiplying the average branch volume by number of branches. Then a volume and biomass relationship was estimated for each species by measuring the biomass of a known volume.
The leaf biomass in the crown was estimated by measuring that in 1m3 of crown volume. Then it was converted to the entire crown via crown volume. Finally above ground tree biomass was calculated by adding branch and crown biomass to stem biomass.
Then allometric relationships were developed to predict the above ground biomass of each of 45 species separately using dbh. A strong relationship was found between total tree biomass and dbh of all species with R2 values over 95%. In order to test further improvement of the models, total height was added as the second explanatory variable. However, it did not improve the R2 and for most species height became non-significant. Therefore the finally selected basic model structure was log biomass = a + b log dbh. The model parameters however, indicated different values for a and b for the different species, varying a from -1.71 (Mastixia tetranda) to - 0.73 (Xylopia parvifolia) and b from 2.01 (Putranjiva zeylanica) to 3.29 (Syzygium cordifolium).
Topics: Forest Management, Silviculture, symposium 2006 |