Determining the optimal rotations of larch plantations when multiple carbon pools and wood products are valued

Abstract

Plantations can provide a large amount of wood products for human society but also have incredible potential to sequester carbon dioxide from the atmosphere due to its growth. However, management of these even-aged plantations to maximize the joint benefits of wood production and carbon sequestration objectives for forest managers and policymakers remains unclear, especially under the stringent targets of 2 °C climatic change mitigation. Therefore, an efficient theoretical framework based on the typical Hartman model was developed in this paper to determine the optimal rotations of even-aged plantations, in which multiple wood products and carbon pools within an infinite time horizon were considered. As an example, the sensitivity of the optimal rotations and their corresponding land expectation values (LEVs) with respect to different carbon pools (i.e., wood products, bioenergy, harvested residuals, stump roots, and naturally generated dead organic matter), as well as a set of stand conditions (site index and stand density) and economic parameters (carbon price and discount rate) were quantitatively evaluated for state-owned larch plantations in northeast China. The results showed that the alternative carbon pools could increase the optimal rotations of larch plantations by 1–3 years for a commonly used management scenario (site index = 16 m, carbon price = 100 CNY/ton)). The optimal rotations decreased linearly with increasing site indices (R2 = 0.95) and initial densities (R2 = 0.98) but increased linearly with increasing carbon prices (R2 = 0.99); however, significant negative exponential trends were observed with increasing discount rates (R2 = 0.92). Except for some extreme cases (site index ≤12 m, discount rate ≥ 6%), the optimal rotations of LEVs are usually larger than those of maximizing sustainable timber yield, in which the differences between them were as much as approximately 4 years of site index (20 m), 6 years of initial density (6666 trees/ha), 15 years of carbon price (1000 CNY/ton) and 9 years of discount rate (3%).