Abstract:

Objective: Increasing forest carbon sequestration has become an important measure to deal with climate change. However, the management of plantation in China is still based on timber income, ignoring the ecological benefits of forests for carbon sequestration. To coordinate the contradiction between carbon sequestration and timber production, this paper aims to explore the optimal rotation period of Larix olgensis plantation by taking into account both carbon sink and wood production, so as to provide a theoretical basis for the multi-objective management of L. olgensis plantation in this area. Method: This study was conducted in 35 plots of Larix olgensis plantation in the experimental forest farm of Northeast Forestry University in Maoershan, Heilongjiang Province. Based on Faustmann-Hartman model, an optimal rotation period determination model of compound management of L. olgensis plantation for both carbon sequestration and timber production was constructed, in comprehensively considering the arbor layer biomass carbon pool, DOM carbon pool, forest product carbon pool. According to the types of carbon pools considered, four different simulation scenarios were designed in this study. Scenario 1 only considers timber benefits, biomass energy benefits and operating costs; Scenario 2 adds additional biomass carbon pool; Scenario 3 further considers the impact of logging residue carbon pool; Scenario 4 adds the impact of carbon release penalties for commercial materials on the basis of Scenario 3. For each simulation scenario, the effects of different carbon prices, discount rates, biomass energy ratios and other factors on the optimal rotation, timber production, carbon sink and land expected value of L. olgensis plantation were quantified. Result: Under the baseline scenario (carbon price: 100 yuan·t^-1 C; discount rate: 5%; the proportion of branch and leaf biomass energy: 20%), the overall expected value of forest land showed a clear trend of first increasing and then decreasing with the increase of stand age, which can be simulated by quadratic multi pattern (Ra² > 0.60). The optimal rotation period for scenarios 1 to 4 was 35 a, and the corresponding forest land expected value was 50 288, 53 638, 53 263 and 53 071 yuan·hm^-2, respectively. For scenarios 2 to 4, the expect value of forest land increased by about 6.66%, 5.92% and 5.53% respectively compared to scenario 1. For Scenarios 2-4, the minimum carbon price that can extend the optimal rotation period of L. olgensis plantation by one year was 1, 500 and 1, 000 and 1000 yuan·t^-1 C, and the corresponding forest land expected values reached 100 667, 80 171 and 78 266 yuan·hm^-2, respectively, with an increase of 87.7%, 50.5% and 47.5% compared with scenario 1. When the discount rate increased from 5% to 9%, the optimal rotation age was advanced by about 4 years, and forest land expect value decreased by about 49 200 yuan·hm^-2. For the same discount rate, there was no significant difference between the optimal rotation period and the expected value of forest land under different simulation scenarios. Conclusion: Under the constraints of the current timber and carbon trading markets, timber revenue still dominates the management of Larix olgensis plantations absolutely. The increase of carbon pool types does not significantly change the optimal rotation age, but it has an impact on the forest land expected value. Carbon price and discount rate can significantly affect the optimal rotation period and land expected value of L. olgensis plantation. The minimum carbon price that can extend the optimal rotation period of L. olgensis plantation by 1 year should be at least 1 000 yuan. t^-1 C.

Key words: Larix olgensis, carbon sequestration, optimal rotation age, Faustmann-Hartman model, carbon pool