Changing forest area and forest productivity - climatic and human causes, effects, monitoring options, and climate mitigation potential

Forests are growing better, and trees are in many places expanding into the alpine zone. In order to maintain biodiversity and fulfill international obligations to reduce greenhouse gas emissions, it is important to understand how changes in the transition zone between forest and alpine will affect vegetation and the potential for carbon sequestration. One of the main goals in FORESTPOTENTIAL has been to analyze how the forest in areas close to the alpine zone will change with a changed climate and changed grazing pressure, and how great the relative effects of these factors are. In the data base for our analyses, we have repeated observations (2008, 2012, 2018) of establishment, growth and mortality for more than 1,500 trees at 36 locations in the transition zone between forest and alpine along a 1,100-km long latitudinal gradient. Linked to each site, we have also had information on grazing pressure, climate and terrain characteristics. Our studies show that it is difficult to quantify general relationships for the effect of changing climate and grazing pressure on the establishment, growth and mortality of trees. Which factors have the strongest impact on the changes seem to differ from site to site. However, our data show that the climate variable that seems to matter most for establishment and growth winter precipitation. This, together with the fact that the terrain form "lee side" and increasing coverage of trees seemed to have a positive impact on establishment and growth, suggests that protection and thus microclimate is important. This points to that changes in the tree line to the greatest extent will be manifested as a densification where the trees are already established, rather than a shift into the alpine zone. Increasing grazing pressure had a negative effect on establishment and grazing will therefore moderate densification. The effect of grazing and climate has also been analyzed using controlled experiments in an area in Hol municipality, where we have used enclosures with different densities of sheep and corresponding field measurements on trees. These analyzes show, like the results from the 36 sites, that sheep grazing influences the establishment of new trees. In parts of the experimental area where sheep were excluded for a 15-year period, the number of small birches decreased significantly when the sheep again were allowed access. On the same areas, the occurrence of the slightly coarser and more established birches was greater compared to the areas where there had been grazing throughout the trial period. This not only suggests that grazing by sheep can change tree line dynamics and the distribution of trees in different stages of development, but also that the current size distribution of trees when grazing is introduced determines what effect the grazing will have. Climate change also affects productivity of existing forests. Monitoring future changes in productivity is important because forest resources are of great importance for activity in the private sector and the country's economy, as well as potential for climate mitigation actions and adaptation. Existing methods for determining productivity are based on average productivity over a tree's lifetime. In times of rapid changes in climate, there is a danger that productivity determined according to conventional methods does not reflect current and future productivity. In FORESTPOTENTIAL, we have developed a method based on remote sensing that is already operational with companies that produce forestry plans for forest owners. The method involves observing trees height growth over a known period of time, and thus determining productivity. The results show that the method is very accurate and will probably take over completely for what was standard until recently. We have carried out an operational, large-scale test in which the effectiveness of the method was compared with the effectiveness of the methods that have been dominant until now. The results showed that the new methods were more cost-effective than the methods they were compared to. In addition to this, the research activities under FORESTPOTENTIAL related to productivity mapping have been continued under the center for research-based innovation (SFI) called SMARTFOREST. FORESTPOTENTIAL will study how changes in forest area and productivity affect economic opportunities in the sector. Scenario analyzes with bio-economic and global equilibrium models that include carbon sequestration will be used to analyze both economic opportunities in forest management and climate mitigation opportunities. This will illustrate the effects of climate change on both nature and society. We have developed an operational forest simulator that will be central to these analyses. The forest simulator has been used to simulate the future development of Norwegian forests under various scenarios, and this data will be the basis for the economic analyses.

The project has established new and stronger networks within and between research groups. This enhanced cooperation will be beneficial in future projects. The enhanced cooperation within MINA, NMBU (project owner) has already led to more joint research efforts in the boreal-alpine ecotone. Based on our unique and large data infrastructure that has been strengthened under ForestPotential, concrete research plans have already been made. These data will be very important for future projects where the aim is to understand the causal relationships between drivers of change and the corresponding changes in vegetation cover and carbon dynamics in the boreal-alpine ecotone. The dataset has also potential to gather many different institutions that do research in this environment and has already spawned research proposals with NINA and Swedish and Finnish partners. The project has strengthened the cooperation with stakeholders, especially Viken Skog and Glommen-Mjøsen Skog. For these two companies, the project has led to a permanent change in their routines for carrying out forest inventories.

FORESTPOTENTIAL will address effects of climate change on forests - both as terrestrial ecosystems and as an important land-based economic sector. Three Research Themes are identified: I) tree dynamics in the boreal-alpine ecotone; II) changes in forest productivity caused by climate change; and III) effects of changing forest resources on (i) economic opportunities in the forest sector and on (ii) mitigation potential accounting for the albedo effect and carbon uptake in biomass and soils. The research is focused on deciphering the effects of climate change and changing land use in the boreal-alpine ecotone and resulting climate feedbacks. We will study how changes in forest area in the boreal-alpine ecotone and forest productivity influence economic opportunities in the sector. Scenario analyses with bio-economic and global economic equilibrium modeling tools accommodating carbon sequestration to consistently address economic management opportunities and climate mitigation options offer a unique opportunity to jointly address effects of climate change on nature and society. For climate adaption, operational methods for monitoring the boreal-alpine ecotone as well as forest productivity are important and will be developed, the latter particularly for land managers. Knowledge of changing productivity has an immediate consequence for the green economy and for climate mitigation by altering the carbon sequestration potential. Thus, climate-induced productivity change has a direct societal impact, and scenario analyses will reveal its potential impact on carbon sequestration and Norway's national climate goals. The research is based on data from field and advanced remote sensing. Guidance on use of remotely sensed data for Greenhouse Gas (GHG) reporting are among the refinements requested by IPCC in guidelines for national GHG inventories. The project will contribute methods to ensure sustainable management of forests and will draw on multidisciplinary approaches.