Legacies of Historical Exploitation of Natural Resources Are More Important Than Summer Warming for Recent Biomass Increases in a Boreal-Arctic Transition Region

摘要

Eurasian forest cover at high northern latitudes (> 67 degrees N) has increased in recent decades due to stimulatory effects of global warming, but other factors may be important. The objective of this study is to compare the importance of historical human exploitation and climate change. Periodic information on forest and tundra resources along with human and domestic animal populations and forest harvesting was collected from sources like official statistics and maps and compiled for joint analysis. Our results show that the northernmost birch and Scots pine forests of the world often presumed as pristine were repeatedly exploited by logging, agriculture and grazing in the last century. In addition, repeated moth outbreaks have also had regulatory impacts on birch forest development. Despite these disturbances, forested area quadrupled during the period, largely because of reduced human activities in recent decades. Linear modelling confirms that the most important predictors for the variation in Scots pine and birch biomass and area were logging, grazing and farming activity, and not climatic changes. The dynamics in the forest cover over the last century seem to follow the 'repeated human perturbation' scenario. This study's application of legacy data, and historical and long-term data and evaluation of how the different drivers impacted some of the northernmost forests are essential to understand whether the greening of the boreal and arctic regions is a result of recent climate change or a recovery from earlier human impacts.