Optimising the management of even-aged Shorea robusta stands in southern Nepal using individual tree growth models

Abstract

This study presents optimal treatment schedules for even-aged Shorea robusta Gaertn. f. stands using varying management objectives. The objective variables used were: total wood production (WP), commercial timber production (CTP), sawlog production (SLP), forest rent (FR) and soil expectation value (SEV). A simulation–optimisation system was developed based on a spatial yield model. The non-linear method of Hooke and Jeeves was used to solve the optimisation problems. The treatment schedules were optimised with zero, one and two thinnings per rotation. Results on two dense five-year-old stands are presented. Irrespective of the management objective, the first thinning was conducted immediately in both the stands. When wood production was maximised the rotation length was short: 6 and 24 years. Treatment schedules for maximal CTP and SEV were relatively similar: the rotation lengths for maximal CTP were 23 and 41 years and for SEV 19 and 51 years for the two stands, respectively. Maximising SLP or FR calls for heavy thinnings and a long rotation: 57 and 85 years for SLP and 52 and 87 years for FR. The mean annual increments of the optimal treatment schedules were 8.5–25.1 m 3 ha −1 a −1 for the total wood production, 6.5–12.1 m 3 ha −1 a −1 for commercial timber production and 4.8–7.6 m 3 ha −1 a −1 for sawlogs.