Optimal management of larch (Larix olgensis A. Henry) plantations in Northeast China when timber production and carbon stock are considered

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The optimal management of larch (Larix olgensis) plantations in Northeast China consisted of 2 or 3 thinnings and a rotation length of 55–61 years when economic profitability, wood production, and carbon sequestration were simultaneously maximized. Wood production ranged from 5.4 to 11.7 m3 ha−1 a−1, depending on site quality. L. olgensis is an important tree species in the northeast forest region of China, playing a significant role in the establishment of fast-growing and high-yielding plantation forests in China. However, the management of these plantations has not been optimized in previous studies. The objective of the study was to find the optimal combinations of thinning times, thinning types, and rotation length for L. olgensis stands when both timber production and carbon stock are considered. First, a growth and yield model was developed to simulate the dynamics of larch plantations. Then, the models were linked with the Hooke and Jeeves optimization algorithm to optimize forest management for two commonly used planting densities and three site qualities. Two thinnings were found to be suitable for larch plantations when the stand density at 10 years was 2125 trees/ha (corresponding to a planting density of 2500 trees/ha) whereas three thinnings were recommended when the density at 10 years was 2800 trees/ha (planting density of 3300 trees/ha). When the stand density was 2800 trees/ha, the optimal rotation length was 61, 58, and 55 years for site indices (SI) 12, 16, and 20 m (dominant height at 30 years), respectively. The mean annual wood production was 5.4 m3 ha−1 for SI 12, 8.2 m3 ha−1 for SI 16, and 11.7 m3 ha−1 for SI 20. The results were nearly the same for the lower initial stand density. The better the site quality of the stand, the earlier the thinnings were conducted. In multifunctional forestry, optimal rotation lengths of larch plantations were 10–20 years longer than advised in the current silvicultural recommendations for Northeast China.