Would spatial yield models be more relevant for forestry operations in the tropics?

Abstract

Experience with companies, using single-tree selection systems for logging in Sarawak, shows that they are generally guided only by basic statutory harvesting rules like minimum diameter limits, maximum gap size and permitted species. At best, silvicultural considerations are typically only implied in the harvesting rules, rather than being explicitly considered in harvest planning and operations. Increasingly, companies are moving towards 100 percent enumeration of trees and tree mapping using GPS as part of reduced or low-impact logging systems. Use of GPS results in a spatial database of trees and key descriptors that could be used to plan future activities by modeling growth and yield to forecast key forest parameters, such as DBH and species, and to map the location of trees. Doing this would help to shift the focus of harvest planners and surveyors from operational to silvicultural considerations such as spacing, recruitment, and future crop trees, when planning harvesting. The main reason why companies are not doing this type of planning now is that the common tropical forest models use area-based parameters (whole stand models, size class models) that are only relevant to large scale planning. Typically these models do not make use of the spatial data that is generated in logging planning, require significantly more and different data that what is used in planning logging operations, and do not produce outputs that are relevant to operational harvest planning. What would be more useful are single-tree models that make use of spatial data, and that produce output that is operationally relevant, including diameter, species, and location of trees. The paper outlines operational requirements of reduced and low-impact logging systems and recommends yield modelling approaches that would work with these systems.