3. Spatial occurrence of drought damages in Finnish boreal forests: GIS and modelling approach
Vitality of forest ecosystems is regularly constrained by water availability and, in addition, drought (i.e. unusually dry and warm weather) may sometimes cause extensive tree damages. Drought has special interest because it may occur in nearly all forest ecosystems and because drought increases tree vulnerability to secondary stresses. The effects of drought damages in forests are influenced by several factors such as soil texture and depth, exposure, species present, life stage and finally the frequency, duration and severity of drought (Dale et al. 2001).
The aim of this work is to examine and model the spatial occurrence of drought damages in the boreal forests in Finland. The scope of this study is to evaluate the potential drought areas and to link that estimate to actual forest condition monitoring. This provides us a tool to predict changes in potential drought regimes in changing climate. We are going to demonstrate how the potential of drought damages differs spatially depending on presumable climatic conditions and soil properties.
The study area covers whole Finland. Finnish forests are mainly characterized by coniferous forests in boreal conditions. Our study is based on the multiple GIS and forest inventory data. One data source is so called Level 1 annual tree crown monitoring data of Pan-European monitoring program ICP Forests (the International Co-operative Programme on the Assessment and Monitoring of Air Pollution Effects on Forests) which was initiated in 1985 and which was established under the UN/ECE Convention on Long-Range Transboundary Air Pollution (CLRTAP). In the Finnish monitoring, drought damages have been surveyed and identified separately since 2005. Thus, we are analyzing monitoring data from 2005 to 2008. The data consists of totally 620 (year 2005), 606 (year 2006), 606 (year 2007) and 488 (year 2008) forest stands based on dividend of permanent sample plots of systematic grid provided by the Finnish National Forest Inventory (NFI). For more details about the NFI see Tomppo et al. (2001). We are also using the Finnish National Forest Inventory (NFI) data itself firstly to study soil quality, secondly to study drought damages and thirdly to study forest biomass and growth. In addition, multi-source forest inventory provides forest parameters based on the combination of remote sensing data and field measurements of NFI (Tomppo et al. 2009). We will combine these forest inventory and forest health data to environmental GIS data provided by national soil database, topographic maps, digital elevation model (DEM) and climatic data.