Temporal evaluation of retention patch development : retention patches in Swedish forestry

Abstract: The demands on the world’s forests are increasing rapidly and the different interests are conflicting, often including goals of biodiversity and timber production. Forest management has since the 1990s included a scientifically validated measure known as retention forestry, to better balance conflicting goals of forest management. It is implemented by leaving portions of stands unlogged to maintain continuity of important structural diversity, facilitate organism dispersal and enhance landscape connectivity. Due to retention forestry being relatively new, there is a lack of knowledge regarding retention forestry maintenance over time. We conducted a spatial analysis on isolated retention patches on clear-cuts in near coastal and inland Västerbotten county, examining areal decreases between 2007 and 2017 in the geographics information system QGIS. Locations, forest cover types, original retention patch size, distance to clear-cut edge and clear-cut ID were the basis for a statistical analysis, assessing if the factors influenced retention patch areal decrease. We found that retention patches in Västerbotten had a mean size of 0.11 ha and that they had decreased to 0.08 ha on average. Furthermore, our statistical model showed that original retention patch size was the only significant factor explaining areal decrease. Earlier studies have stated that the main cause for retention patch reduction is wind effects and exposure, something our project did not account for. The results showed that larger retention patches had lower percentage decreases compared to smaller retention patches. For future studies, more data and variables should be used, possibly over a larger timespan and geographical range.