Optimising the management of uneven-aged Pinus sylvestris L. and Pinus nigra Arn. mixed stands in Catalonia, north-east Spain

Abstract

This study uses a simulation-optimisation system, PINUSMIX, to optimise the structure and management of uneven-aged mixtures of Pinus sylvestris L. and Pinus nigra Arn. in Catalonia (north-east Spain). The simulation sub-system consists of a method for drawing the initial tree diameters from a Weibull distribution and a stand growth and yield simulator based on individual-tree growth, height, ingrowth and survival models. The simulation sub-system was combined with the optimisation algorithm of Hooke and Jeeves. The system was used to optimise the management of uneven-aged mixtures of P. sylvestris and P. nigra on medium site characteristics in the region. When the land expectation value with a 20-year cutting cycle and a 2% discounting rate was maximized, the land expectation value was 1331 euro ha-1, and the optimal prior-thinning stand volume was 86 m3 ha-1. In the optimal stand structure P. sylvestris dominated. The effects of discounting rate, cutting cycle length, objective function, site, timber prices, type of diameter distribution and biodiversity considerations were logical. Increasing discounting rate and shortening the cutting cycle decreased the optimal prior-thinning stand densities. Maximising wood production or net income resulted in higher volumes of growing stock than did maximising profitability. Forcing the inclusion of large trees in the stand, for biodiversity reasons, clearly decreased profitability but had no effect on wood production. © INRA, EDP Sciences, 2005.