Multi-purpose forest management in the tropics: Incorporating values of carbon, biodiversity and timber in managing Tectona grandis (teak) plantations in Costa Rica

摘要

Plantation forestry is the ultimate alternative in reforesting degraded tropical ecosystems and in provisioning multiple ecosystem services beyond timber production. Therefore, we studied the management of Tectona grandis L.f. (teak) plantations in Costa Rica and simulated alternative management strategies incorporating simultaneously the values of carbon storage, biodiversity and timber production. Alternative management strategies included (1) extension of rotations, (2) reduced thinning and (3) conversion of even-aged to uneven-aged systems. Evaluation criteria were carbon storage in biomass, stand structural diversity as a proxy of biodiversity, and economic return from timber harvests. For growth predictions under future climatic conditions, we calibrated the hybrid forest growth model 3PG. We found that carbon storage could be increased by increasing rotation periods (e.g. + 29.7% of carbon for a 50% increase in rotation length) and a no thinning management (+ 9.5% of carbon). For rotation extension associated economic losses were high (e.g. at 5% discount rate, the Land Expectation Value (LEV) decreased by 25.1% for a 50% extension of rotations). For thinning LEV increased with a low-thinning regime, but decreased with a no-thinning management (+ 9.5% and 23.6%, respectively). Payments for ecosystem services (PES) increased economic return by about 3-4%. Structural diversity increased by conversion to uneven-aged forest stands (Gini coefficients for basal area increased from 0.21 to 0.52). Economic returns from timber harvests were almost equal for even-aged and uneven-aged systems at 1% discount rate (max. -2% of LEV). At 5% discount rate, we observed economic losses of 11.1-20.1% compared to the even-aged scenario. At 10% discount rate, economic losses ranged between 43.6 and 104%. We concluded that extension of rotations and reduction of thinning intensity can be used as management strategies to increase the carbon storage of teak plantations. However, to compensate the associated economic losses through a PES scheme, payments for carbon sequestration need to be increased and special incentives for longer rotation periods and low thinning management need to be developed. The transformation into uneven-aged forest stands requires active investment at discount rates higher than 1%. Whether this investment can be offset by benefits from biodiversity and increased forest resilience is unknown and requires further investigations. Other measures of biodiversity conservation, such as the use of native and mixed tree species and the retention of old trees and deadwood are moreover necessary.