Sustainable timber harvesting in Venezuela: a modelling approach
Reliable data on the growth and yield of logged-over forest to determinesustainable cutting cycles are widely missing for the tropics. We used theprocess-based model Formind2.0 to analyse the growth and yield of logged-overforest in Venezuela under different logging scenarios over a period of 240years and compared results with unlogged stands.The performance of the modelwas evaluated with a detailed stability and sensitivity analysis.In theabsence of further logging,the logged-over stand approached the standstructure of mature forest in terms of bole volume and basal area afterabout 50-100 years.Thirty-year cutting cycles with conventional loggingmethods and net extraction volumes of 45 and 60 m^3/(ha cycle) did not providesustainable yields under either of two minimum felling diameters(35 or 50 cm) that were applied. Only the 60-year cutting cycle providedsustainable yields under conventional and reduced-impact logging with thedi minimum felling diameters and a range of net volumes extracted(30-60 m^3/(ha cycle). With the longest cutting cycle (60 years), bole volumerecovered to levels similar to the mature unlogged stand, but the speciescomposition was very different.Scenarios with reduced-impact logging provideda significantly higher timber volume than under conventional logging. Theconservation of forest resources will only be possible with long cuttingcycles (at least 60 years) in combination with reduced-impact logging.