Die-off dynamics of Siberian larch under the impact of pollutants emitted by Norilsk enterprises

The radial growth of Siberian larch under the impact of pollutants emitted by enterprises of Norilsk has been analyzed to reconstruct the die-off dynamics of larch stands located along the Rybnaya River, along the main direction of pollutant air transport. Dendrochronological cross dating is used to detect the year of die off of 268 trees growing in 4 sites located 22, 45, 68, and 85 km from Norilsk. The death of individual trees in the sites closest to Norilsk was recorded immediately after the first enterprises started to operate in the early 1940s. The mass mortality of the trees started in the 1960s due to the operation of new smelters and the consequent increase in pollutant emissions. The complete destruction of the stands (100% die off of larch trees) occurred in the 1970s. At the most distant site (85 km), the highest rate of larch death was observed between 1975 and 1980, and in 2004 only 23% of larch trees were alive. A comparative analysis of the tree-ring width of the studied trees testified to the decrease in tree radial growth at the period before the complete degradation of stands. Unfavorable climatic conditions became an additional factor that enhanced the rate of tree die off due to the impact of pollutants. Although the increase in tree radial growth had been found in late 1990s to early 2000s at the site 85 km from Norilsk, the status of studied trees indicated that the area of completely degraded forest ecosystems might become larger under the present conditions.