Modelling cowberry (Vaccinium vitis-idaea) and bilberry (Vaccinium myrtillus) yields from mineral soils and peatlands on the basis of visual field estimates.

This study presents new models for predicting bilberry and cowberry yields from site and stand characteristics. These models enable one to evaluate th e future states of forests in terms of berry yields. The modelling data con sisted of visual field estimates of site and tree stand characteristics. as well as berry yields from 627 forest stands. Berry yields were estimated u sing a scale from 0 to 10. Using these data, models were prepared which pre dict the berry yield scores from those site and stand characteristics which are usually known in forest planning calculations. The model predictions c orrelated positively and often quite strongly with earlier models. The resu lts were in line with previous studies on the effects of site and tree cove r on berry production. According to the models, sites of medium and rather poor fertility produce the highest bilberry yields. Increasing tree height increases, and the basal area of spruce and proportion of deciduous trees d ecrease, bilberry yield. With mineral soils, cowberry yields are best on po or sites. A high proportion of pine improves cowberry yields. The yields ar e the highest in open areas and very young stands, on the one hand, and in sparsely populated stands of large and old trees, on the other hand. In pin e swamps, the yields are best on rather poor sites. Increasing basal area o f deciduous trees decreases cowberry yields.