Impacts of rotation age changes on growth/removals ratios

Abstract

When forest managers and policymakers wish to assess the ability of a given forest resource to support a sustainable level of timber harvests, they frequently use growth/removals ratios (G/R) developed from forest inventory data. Recently published inventory data for forests of the southern United States have documented numerous states in which softwood harvests exceed softwood growth, raising concern over the sustainability of this critical resource. At the same time, forest managers in the South have been investing in a wide range of practices that have dramatically increased the growth rates for softwood plantations. As these growth increases are verified in the field, forest managers respond accordingly with adjustments to management regimes, including shortening of rotation lengths. This, in turn, means that the area of forest harvested annually must increase in a given forest estate to approach a regulated forest condition. The Timber Inventory, Growth, and Removals model (TIGR) is a spreadsheet model developed to evaluate the impact of shortening rotation length on the growth/removals ratios for managed forests. The model demonstrates that a temporary imbalance of removals over growth results when the rotation age is shortened. Hence, managers and policymakers should use caution when making inferences or public claims about sustainable harvest levels from growth/removals ratios alone. If the public has been convinced that G/R ratios greater than 1.0 imply sustainable harvests, then difficult explanations will be required when the G/R ratio drops below 1.0. South. J. Appl. For.