Habitat quality assessment using Weights-of-Evidence based GIS modelling:: The case of Picoides tridactylus as species indicator of the biodiversity value of the Finnish forest

Biodiversity issues have gained importance in forestry as a result of the increased awareness of forest landscape changes, but still there is much to do before forest management meets reasonable goals for forest protection and renewal of biodiversity. In this work, we focus on boreal forest landscapes, using Finland as a case study, and taking advantage of a valuable database-the National Forest Inventory (NFI). We explore a multicriteria approach by using a predictive habitat suitability model for three-toed woodpecker (Picoides tridactyius) based on Weights-of-Evidence (WofE) and a combination of remote sensing and field data derived from the Multisource Finnish National Forest Inventory (MS-NFI). The WofE model is a quantitative method used for combining evidence to examine the support for a given hypothesis. WE involves the estimation of a response variable (favourability for certain habitat occurrence) and a set of predictor variables (e.g. GIS layers containing environmental variables). WE is based on a log-linear form of Bayes' rule and uses the prior probability distribution and the likelihood of the data to generate a posterior probability distribution. Very few examples exist of WbfE being used to predict the spatial distribution of species or communities using biophysical descriptors. This work explores WofE as a tool for rapid biodiversity assessment using georeferenced species information. Since the method is dependent of the indicator species used as a surrogate of biodiversity value it can be applied for assessing biodiversity conditions of both managed and protected areas to help decision-making concerning protection of valuable habitats. Thus, the map of habitat suitability; represented as a range of probabilities of occurrence, offers an objective framework for evaluating the outcomes of different scenarios. Similarly, an objective assessment of habitat suitability provides a rational basis for management decisions incorporating impact on species habitat.