Optimal multi-product management of stands producing timber and wild berries

Abstract

Northern wild bilberries (Vaccinium myrtillus) and cowberries (V. vitis-idaea) are increasingly demanded, and forest owners are interested in their contribution to the total income obtained from the forest. In this study, bilberry and cowberry yield models were included in a stand growth simulator and the joint production of timber and berries was optimized by maximizing soil expectation value (SEV) with 3 % discount rate, assuming that 75 % of the berry yield is harvested. The berry prices and picking costs were included in calculations. Management was optimized for the following three stand types: Scots pine stand on Myrtillus site, mixed stand of Scots pine, Norway spruce and birch on Myrtillus site, and Scots pine stand on Vaccinium site. Management was optimized separately for an average and a good berry stand. With the current berry prices and picking costs, the optimal management of average berry stands changed very little from the timber-oriented stand management. When a pine stand growing on Vaccinium site produced good cowberry yields, thinnings were heavier and the rotation length was a few years longer than obtained for average berry stands. When both bilberry and cowberry yields were included in optimization, the optimal rotation length was 36 years longer than in timber-oriented management. In pine stands and mixed stands of pine, spruce and birch growing on Myrtillus site and having good bilberry yields, about 20 years longer rotation and a heavier first thinning were optimal to reduce canopy shading to a level that is favorable for bilberry crops. With increasing berry prices, it was more profitable to apply still longer rotation lengths and higher thinning intensities and convert the mixed stand into a pine–birch mixture—instead of spruce dominance—toward the end of the rotation. With the current berry prices, the SEV calculated with berries was more than twice as high as the SEV calculated without berries. Valuing forest berries may remarkably change the optimal management of stands, where the berry yields are known to be or can be assumed to become high.