Estimating Tree Volume

The plot method described in Chapter 10 provides values for tree parameters such as DBH and height. These values could be used to estimate the volume of the tress, which can be converted into weight terms using wood density. This method involves the following steps:

Step 1: Measure the height and DBH of all the trees in the sample plots (following Chapter 10).

Step 2: Tabulate the values of height and DBH by species and by plot. Step 3: Estimate the volume of each tree in the sample plot using the following formulae depending on the shape of the tree, whether cylindrical or conical.

where:

V = volume of the tree in cubic centimetres or cubic metres r = radius of the tree 130 cm above the ground = DBH/2 H = height of the tree in centimetres or metres.

Step 4: Obtain the wood density value for each of the tree species from literature (refer to Section 17.7), at least for the dominant species

° If the density value for any dominant tree species is not available in the literature, select the species most closely related to the species present in the site.

Step 5: Multiply the volume of the tree with the respective wood density to obtain the dry weight of that tree and convert the weight from grams to kilograms or tonnes.

° Weight of tree (in g) = volume of the tree (in cm3) x density (g/cm3)

Step 6: Sum the weight of all trees of each species in the selected sample plots (in kilograms or tonnes for each species). Step 7: Sum the weight of all the trees of all tree species for all the sample plots, based on the weight calculated for each plot (in kilograms or tonnes). Step 8: Extrapolate the weight of each species from the total sample area (sum of all the plots) to per hectare value (tonnes of biomass per hectare for each species). Step 9 Sum the biomass of each species to obtain the total biomass of all the trees in tonnes per hectare (dry matter).

17.1.2.1 Additional Steps for Estimating the Biomass Using Volume

Estimation of wood density The density of wood varies with species, age and even component of tree biomass (main trunk, branches and tender twigs). Thus, it is a good practice to estimate the density of the tree species present in the selected plots, especially if literature values are not available for that species. The following steps could be adopted to estimate the density of wood:

Step 1: Select the tree species and components for which density has to be estimated Step 2. Extract a piece of wood by drilling or by cutting; collect three to five such pieces Step 3: Take the fresh weight of each piece of wood (in grams) Step 4: Dry the wood sample in an oven at 105°C to constant weight Step 5: Take a graduated measuring jar of known dimensions and volume, of a size convenient for immersing the piece of wood using a pointed needle, to measure the amount of water displaced Step 6: Record the height of the water and then immerse the piece of wood into water in the measuring jar and measure the increased height of the water in the jar and ensure that the piece of wood is completely submerged in water Step 7: Estimate the volume of the piece of wood in cubic centimetres (cm3), based on the height of the water raised and the radius of the jar

where:

V = volume of the piece of wood in cubic centimetres r = radius of the jar in centimetres

H = increase in the height of the column of water on immersing the piece of wood in centimetres

Step 8: estimate the density of the wood (D) using the following formula:

D (in g/cm3) = weight of the piece of the dry wood (in g)/ volume of the piece of wood (in cm3)

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