RADIAL GROWTH OF TREES IN ANTHROPOGENICALLY MODIFIED LARCH FOREST OF THE CRYOLITHOZONE

The effect of anthropogenic impact (cutting of a «winter road» in 1984, in effect until 2002) on the radial growth dynamics of Gmelin larch trees ( Larix gmelinii (Rupr.) Rupr.), growing in permafrost larch forest has been analyzed. It has been established, that after the construction of the winter road the tree ring widths of the trees within the anthropogenically disturbed area increased sharply and after several years reached the peak values (0.971-1.601) mm, while in the natural stand it remained at the level of 0.121 ± 0.003 mm. Measurements showed that at the end of August (2017) the seasonally thawing layers on the abandoned road site and on the forest edge site (119.1 ± 18.4 and 71.9 ± 6.8 cm) were significantly larger than that in the natural stand (54.8 ± 5.8 cm). I.e., in the latter the temperature of the seasonally thawing layer increased faster and took on higher values. Using sliding climatic response functions of the radial increment indices, we revealed that anthropogenic impact modified the response of the trees to the influence of climatic factors. They manifested an earlier, in comparison with the natural stand, reaction of trees to spring-early summer air temperatures that show an earlier start of growth of the annual ring. We revealed also longer (end of May - end of June) dependence of the trees growing on the forest edge to precipitation compared to the native forest (end of May - beginning of June). We concluded that the modifications of the climatic response and a sharp increase of radial increment were due to the improvement of hydrothermal growth conditions in the anthropogenically disturbed area. Using extrapolation of the radial growth curves to future period of time, we can come to recognize that after finishing exploitation of the road in 2002, hydrothermal soil conditions and tree ring values in the anthropogenically modified forest sites will «return» to the background state in about 30 years, which is similar to post-pyrogenic restoration. Taking into account post-anthropogenic long-term effect manifested in improving the hydrothermal growth conditions, reducing the thickness of the organic layer and the formation of larger radial growth increments, the estimations of carbon balance in boreal forests growing on permafrost soils will make a significant improvement.

radial increment, Gmelin larch, anthropogenic impact, hydrothermal soil conditions, climate factors