# Subarctic Vegetation under the Mixed Warming and Air Pollution Influence
## 3 Results
### Tree Growth and Mortality Dynamics  
The first official data regarding pollution-driven forest dieback referred to 1970 [35]. At that time, the total area of dead forests was estimated as c. 5000 ha (red curve on Figures 6d and A1). Since then, a team of foresters from the State Forest Service have been surveying decline and mortality based on the on-ground and airborne data. Thus, in 1986 (the date of the last survey), the areas of total mortality and weakened forests were approximately 300,000 and 550,000 ha, respectively (Figure A1). Later, forest status was usually estimated based on satellite data, with occasional on-ground studies. According  
Figure 5: (**a–d**) Examples of sulfur dioxide transfer (based on Copernicus Sentinel-5P data [25]). SO\({}_{2}\) pollution spreads to a distance of several hundred km. The scale of SO\({}_{2}\) concentrations at the 7 km altitude is presented in (**a**). (**e**) The wind rose. Northwestern wind prevailed in summer, whereas southeastern ones prevailed in winter. to the latest satellite-derived estimate, the total area of dead and weakened vegetation communities was c. 24,000 km\({}^{2}\)[7]. The comparative GI dynamics of larch trees in the reference, LSB (larch-spruce-birch mixed forest), and impact zones are presented in Figure 6a-c. In the impact zone, tree population was divided into \"decliners\" (i.e., trees that eventually died) and \"survivors\" cohorts. The growth index of larch in the impact zone (especially \"decliners\") has had a significant negative trend since the 1950s until the beginning of the 2000s, whereas in the LSB zone, the trend is significantly lower (Figure 6c). In the reference zone, variations in the GI correlated with air temperature, whereas in the impact and LSB zones variations were  
Figure 6: GI dynamics of larch trees in the (**a**) reference and (**b**) LSB zone. (**c**) Comparative GI dynamics of “survivors” and “decliners” larch trees and sulfur dioxide emission in the impact zone. Solid lines indicate an 11-year moving average. (**d**) Tree mortality dates (gray columns; dendrochronology-derived values) and the total area of dead and weakened forests (red curve; based on [35] data; see also Figure 11). Mortality is the percent of trees that died in the given year. Stars (*) indicate significant trends at \(p<0.05\). meditated by both warming and SO\({}_{2}\) emissions (see equations in Table 2). In the impact zone, decliners' mortality was observed until c. 2005 (Figure 6d), whereas survived trees have increased growth since the end of the 1990s (Figure 6c). A similar positive trend was also observed in the reference zone (Figure 6a). Synchronous variations of the GI in all zones can be attributed to the variations in the temperature, which is, along with sulfur dioxide, a primary factor of tree growth. As for bushes (willow and alder), the GI dynamics of willow are similar to trees in the LSB zone, i.e., without significant depression in the 1990s, whereas the GI of alder is similar to larch tree growth in the impact zone. Both species increased growth since the 2000s (Figure 8a,b).