Compatible taper and volume equations for yellow-poplar in West Virginia

Compatible segmented polynomial taper and volume functions were developed for yellow-poplar (Liriodendron tulipifera L.) from two ecoregions of West Virginia. The data were based on stem analysis of 26 trees from the Central Appalachian Broadleaf Forest province in northern West Virginia and 18 trees from the Eastern Broadleaf Forest province in west central West Virginia. Sample disks were extracted from 0.3, 0.6, 1.37, 1.8 m and then every 1.2 m to an approximate 7.6 cm top diameter outside bark. Sample trees ranged from 17.3 to 56.1 cm in diameter and from 18.8 to 38.5 m in total height. Model forms developed by Max and Burkhart [Max, T.A., Burkhart, H.E., 1976. Segmented polynomial regression applied to taper equations. For. Sci. 22, 283-289] and Clark et al. [Clark III, A., Souter, R.A., Schlaegel, B.E., 1991. Stem profile equations for southern tree species. USDA For. Serv. Res. Pap. SE-282] as well as two reduced forms of Clark et al. [Clark III, A., Souter, R.A., Schlaegel, B.E., 1991. Stem profile equations for southern tree species. USDA For. Serv. Res. Pap. SE-282] model were fitted to both inside and outside bark data. Outside bark taper prediction error for the proposed reduced model form using the fitted dataset had an average bias of 0.0153 cm and a standard error of the estimate of 1.2798 cm, based on the results from Central Appalachian Broadleaf Forest province. Volume prediction error for the same model and location had an average bias of −0.00002 m3 and a standard error of the estimate of 0.0045 m3. Tests with an independent dataset from northern West Virginia showed the proposed reduced model form had the lowest overall outside bark prediction error as well as having the smallest error in five of the seven relative height classes tested.