Regulation of Timber Yield Sustainability for Tropical and Subtropical Moist Forests: Ecosilvicultural Paradigms and Economic Constraints

Components of yield regulation systems are discussed which are required to ensure successful stand regeneration and sustainable timber yield optimization in tropical and subtropical moist forests. Existing yield regulation/silvicultural systems were classified into four groups: uniform systems, tropical shelterwood systems, manipulistic selection cutting systems and naturalistic selection cutting systems. The performance of these systems, in particular of the relatively high impact systems generally practiced in the tropics, was assessed and problems relating to inadequate regeneration, unsustainable timber harvest levels, inadequacies of the residual growing stock and neglect of silvicultural interventions are identified. Most systems, as practiced, are potentially subject to sustainability risks due to forest matrix destruction effects, disruption of functional interspecies dynamics and disruption of regeneration processes. A forest matrix invasion model, which is considered to explain tropical forest dynamics ecologically more closely than the successional disturbance model generally invoked for temperate forests, is outlined. Based on this model, timber yield regulation characteristics for continuous cover primary forest management were defined. They include large-tree productivity realization, relative high harvest maturity thresholds and residual growing stock levels, and protection of the forest matrix through reduced impact logging.