A generic model of thinning and stand density effects on forest growth, mortality and net increment

For assessing forest thinning effects at large (i.e. continental) scale, data scarcity and technical limitations prevent the application of localized or individual-based thinning models. Here we present a simple general framework to analyze and predict the effects of thinning on growth and mortality, including the following stand density development. The effects are modeled in relative terms so that the model can be parameterized based on any thinning experiment that includes an unthinned control, regardless of site conditions and stand age. The model was tested against observed thinning effects on growth and mortality from five temperate and boreal species (all species pooled r(2) = 0.51). It predicted a maximum increase in net stem biomass increment of 16% and a reduction in density-related mortality of 75% compared to unthinned conditions at stand densities of around 70% of the maximum (increment optimal density). A sensitivity analysis revealed overlapping ranges of near optimal density (net increment within 95% of optimal) among all tested species, suggesting that one thinning scenario can be used for many species. The simple and general formulation of thinning effects based on only five parameters allows easy integration with a wide range of generic forest growth models.