Tree Change in Nemoral Spruce Forests of the Central Forest Reserve

Abstract

The paper discusses changes in forest-forming species in the nemoral spruce forests of the Central Forest Reserve (Tver Region, the Russian Federation). A comparison is made of the characterization of vegetation in the reserve spruce forests, carried out during the first survey of the reserve by Ya. Ya. Alekseev in 1931 (Alekseev, 1935) with the descriptions of vegetation made by the author from 2011 to 2019. It is shown that the coverage of nemoral herbs in the spruce forests of the reserve has increased over the past 90 years. In addition, three types of broadleaf trees (Tilia cordata Mill., Acer platanoides L. and Ulmus scabra Mill.) have greatly increased their abundance in the stand, most notably the linden. In recent decades, the decay of nemoral spruce forests has been taking place in the Central Forest Reserve. The birch-aspenspruce stand is not replenished with spruce renewal but is replaced by linden-maple forests. The vitality of spruce undergrowth is deteriorating. After the decay of a spruce forest, a change of the tree dominants occurs on 74% of the trial plots and the stand continues with a spruce forest on 26%. The largest part of the reserve's nemoral spruce forests arose after major disturbances 100–150 years ago (on the site of burned-out areas, hurricane windblows and cuttings). Old nemoral spruce forests were formed during the period when severe frosts prevented linden and maple from entering the stand. Currently, the coincidence of climate warming with the aging of the spruce stand and the removal of anthropogenic influence contributed to the release of maple and linden from the undergrowth into the stand and change to a spruce-deciduous forest. Under the prevailing climatic conditions, a return to the spruce forest is possible in the event of a burning out or when the climate becomes cold. The nemoral spruce forest is an ecotone type and, depending on conditions, becomes a spruce or broad-leaved forest.