Regional expert models for bilberry and cowberry yields in Finland

This study presents regional berry yield prediction models for the 13 Forestry Centres of Finland. The study material was collected by mailing a questionnaire to Forestry Centres' forest planners and other staff members whose work was related to forest planning in the field. These persons assessed bilberry and cowberry production of 117 imaginary forest stands, differing in site fertility, dominant tree species, stage of stand development and stand density. A total of 266 regional experts evaluated the stands. Using the resulting data, models were prepared which predict the berry yields from those site and stand characteristics which are usually known in forest planning calculations. In bilberry modelling, two separate models were developed: one for the Forestry Centre of Kainuu and the other for the rest of Finland. In cowberry modelling, the statistical analyses resulted in the sub-division of (1) North Karelia, Kainuu and Lapland vs. (2) the rest of Finland. Several district-specific, or Forestry Centre-specific, predictors were included in models common to several Forestry Centres. The results of this study, based on unexceptionally wide regional expertise, on the effects of site and tree cover on berry production were largely in line with previous field and other studies conducted in some parts of Finland. The models developed can be utilised in multiple-use forest planning throughout the whole Finland. They also provide possibilities for estimating the regional supply of the major wild berries in Finland. However, there still remains a need to calibrate the models with field data.