Construction and validation of models for timber volume of poplar (Populus deltoides) planted in agroforestry in Haryana
Rizvi RH., Khare D., Handa AK.
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 'D 2 H' 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 (m 3 ), was adjudged best for predicting the timber volume using 'D' with mean absolute error of 0.029 m 3 . On the other hand, the Chapman-Richards model, i e V = 0.705 [1-exp (-0.394×D 2 H)] 0.976 found best among 5 models fitted using 'D2H' with mean absolute error of only 0.023 m 3 . Hence the proposed models may be used for predicting the timber volume (over bark) of P. deltoides tree in Haryana region.