Selecting reserves for forest biodiversity maintenance is often done by setting criteria for components of structural elements of biodiversity, such as a volume of decaying wood. We tested how the different threshold values for the components of structural elements affect the cost-effective site selection. Using Finnish National Forest Inventory information and remote sensing data, we determined a habitat quality index and economic value for each site in Satakunta region in Finland. Moreover, we defined several sets of potential conservation targets using alternative criteria for the habitat quality index developed for the Finnish case study. These figures were used in the site selection model in order to maximize the sum of habitat index of selected areas under a given budget constraint. We found that the production possibility frontier for the outputs of timber and biodiversity is only slightly concave when using the given threshold values. Thus, the optimal combination of the outputs is sensitive to the relative values of these goods. Our results suggest that an integrated approach in forest conservation could provide to environmental managers considerable cost savings compared with current management practices. Environmental managers could also reduce conservation costs by loosening the criteria for potential conservation targets. This would not lower considerably the quality of conserved forests.