Volume and Biomass Functions for Trees Grown under Arid Conditions in India

Volume equations are critical starting points to make forest management successful and efficient. Allometric equations for predicting total and merchantable volume play a critical and obvious role in the management of any silvicultural system. The importance of volume equations is indicated by the existence of numerous such equations and the constant search for their improvement. The objective of any volume equation is to provide accurate estimates with acceptable levels of local bias over the entire diameter range in the data. Equations that provide accurate predictions of volume without local bias over the entire range of diameter are one of the basic building blocks of a forest growth and yield simulation system.

In this article, volume equations for Eucalyptus camaldulensis, Dalbergia sissoo and Tecomella undulata planted in Indira Gandhi Nahar Pariyojana (IGNP) area of Arid Rajasthan and Acacia nilotica and Eucalyptus hybrid stands in Gujarat state in India are presented. Apart from this, biomass equations for Azadirechta india planted in Gujarat are also reported. The biomass equations for each component were derived independently. The component predictions are not additive which implies that the predicted weight of stem plus branches may not be equal to the sum of the predicted values of stem and branch. The volume and biomass equations are extremely useful in estimating above-ground carbon stock in these species and in preparation of carbon tables.

Linear and non-linear equations were used to model the relationship of total volume and/or biomass with dbh, and with dbh and total height of the trees, and were compared on the basis of fit and validation statistics. An equation that fits very well to a data set may not necessarily be the best when applied to another data set collected from the same population. The contrasting results, obtained between model fitting and validation, emphasize the need for model validation as an important step in the model construction process.