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Allometric Relationships for Predicting the Stem Volume in a Dalbergia Sissoo Roxb. Plantation in Bangladesh

NI Khan
Department Forest Biometry and Systems Analysis, Institute of Forest Growth and Forest Computer Sciences, TU Dresden, P.O. Box 1117, D-01735 Tharandt (Germany)

O Faruque
Forestry and Wood Technology Discipline, Khulna University, 9208 Khulna (Bangladesh)

Abstract/ Executive Summary:

Allometric relationships for estimating stem volumes of Dalbergia sissoo Roxb. (Sissoo) trees were investigated in monoculture plantations in Bangladesh. The various allometric relationships between stem volume and different dimensions were tested and the coefficient of determination R² values were used to compare the strength of the relationships. Although the allometric equations were highly significant (P<0.01) there was considerable variation among them as indicated by the R² values. Our results suggested that tree volume is more correlated with basal area than with simple D (stem diameter at 1.3 m height above the ground). The allometric relationships of stem volume to the tree diameter at 10% of tree height (D_0.1) did not improve the allometric strength in comparison with simple D as reported in case of some other tree species. The multiplication of tree height H with D in the allometric equation gives a little improvement in the degree of fitness of the allometric equations. However, for the Sissoo plantations studied the stem dbh alone showed a very strong accuracy of estimation (R² = 0.997) especially when used as D². It is concluded that the use of tree height in the allometric equation can be neglected for the species, as far as the present study area is concerned. Therefore, for estimating the stem volume of Sissoo, the use of D² as an independent variable in the allometric equation with a linear or quadratic equation is recommended. The paper describes details of tree volume allometry, which is important in silviculture and forest management.

Keywords: Allometry, Monoculture plantation, Regression, Rosewood, Sissoo, Stem volume

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End Date:

Program Area: Socio-economic and Policy

Commodity: Agar

Objectives:

In this paper, we seek to establish the allometric relationships of the stem volume of individual trees to different dimensions, such as D, D², D²H, D_0.1, D_0.1² and D_0.1²H and to propose a standard method for predicting the stem volume of Sissoo.

Methodology:

Study site and species description: The study was carried out in block plantations at Khulna located in the southern part of Bangladesh. The area belongs to subtropical region. Dalbergia sissoo is one of the important plantation species in the region. The species is a strong-light demander and shows good coppicing ability. The development of seedling is better in full overhead light than under partial shade. It is capable of growing under adverse soil and moisture conditions. Though, D. sissoo is a frost hardy species, its young leaves are adversely affected by severe frost and even the poles get completely defoliated. It has a complex root system that consists of a deep tap root and long lateral roots. Root suckers are produced from the lateral roots. Root suckers develop towards the end of the rainy season and may attain a height of more than 2 m on good soil. The species can grow naturally up to 1500 m elevation. The temperature in its native range averages 12-22 °C, but varies from just below freezing to nearly 50 °C with an average annual rainfall of 500 to 2000 mm with a monsoonal pattern and drought period of 3-4 months ([35]). The growth of the bole is crooked and straight logs of any great length are difficult to obtain. The heartwood is brown with darker streaks and because of its strength and durability, the wood is highly valued for furniture, constructional and general utility purposes.

Sampling, data collection and analysis: All the studies were carried out in May 2006 in a monoculture plantation of D. sissoo where the canopy was completely closed. A destructive sampling of 30 individual trees with a wide range of diameter and height were used for this study. The following measurements were carried out: tree height H, stem diameter at a height of H/10 (D_0.1 -, stem dbh D and stem diameter at 1.0 m interval thereafter up to the merchantable height (stem height at 10 cm diameter). For measuring the diameter, girth values were converted to diameter after divided with π. Stem volume was calculated using the Smalian’s formula.

The simple allometric equation is generally written using the power curve ([17]) in the form (eqn. 1):

y = a x b (1)

where y is the dependent variable and x is the independent variable, and a the coefficient and b the allometric constant. The equation is linearized by taking logarithms, as follows (eqn. 2):

l n (y) = l n (a) + b \cdot l n (x) (2)

where ln a and b are the intercept and slope of the regression line, respectively. The ln a and b are obtained by the method of least squares. In this study, the allometric relationships of the volume and different dimensions such as D, D², D²H, D_0.1, D_0.1² and D_0.1²H

Source of Information: iForest - Biogeosciences and Forestry, Volume 3, Issue 6, Pages 153-158 (2010)

Article Link (Online Journal): doi: https://doi.org/10.3832/ifor0554-003

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Achievement/Findings:

The findings of this study indicate that there is a variation in the use of independent variables in allometric equations for estimating the stem volume of the species. The allometric relationships described in this paper may not be appropriate in mixed or open forest stands, because the present study was carried out under monospecific and closed canopy conditions. For estimation stem volume of trees outside the size range of this investigation, care should be taken in extrapolating the present allometric relationships. Therefore, users of these allometric equations are recommended to check some individual trees outside the present size class.

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