Construction and validation of models for timber volume of poplar (Populus deltoides) planted in agroforestry in Haryana

Sixty Populas deltoides trees of ages 6, 7 and 8 years were selected from agroforestry plantations in Haryana. The growth (height, bole height and dbh) and timber volume (over bark) data was recorded/computed for these trees. The 5 nonlinear functions, viz Logistic, Gompertz, Chapman-Richards, Weibull and Sloboda were fitted using 'D' and 'D2H' as explanatory variables; where D, diameter at breast height (cm), H, height of tree (m). These fitted models were validated statistically and graphically using data splitting procedure. The Gompertz model, i e V = 1.002 exp (-6.355 e -0062*D), where V-timber volume (m3), was adjudged best for predicting the timber volume using 'D' with mean absolute error of 0.029 m3. On the other hand, the Chapman-Richards model, i e V = 0.705 [1-exp (-0.394×D2H)]0.976 found best among 5 models fitted using 'D2H' with mean absolute error of only 0.023 m3. Hence the proposed models may be used for predicting the timber volume (over bark) of P. deltoides tree in Haryana region.