Reconstruction of the Disturbance History of Bilberry–Sphagnum Spruce Forests in the Central Forest Reserve

A study of bilberry–sphagnum spruce forests (from Picea abies (L.) H. Karst.) in the Central Forest Reserve (Tver oblast, southern taiga) is presented. The sample plots covered 7 km2 of forest. Coals were found under the roots of fallen trees in all the test areas. Reconstruction of the history of disturbances based on spruce cores showed that the surveyed area was subjected to high-intensity fires in the 1770s–1780s and 1840s–1870s. In addition, part of the spruce forest experienced major wind disturbances in the 1900s (reconstruction), as well as in 1987, 1996, and 2017/2018, as well as the mass drying of spruce in the 2010s and 2020s. Over the past 250 years, there has been a decrease in the frequency of pyrogenic disturbances and an increase in wind damage. The rarity of fires since the second half of the 20th century is an obvious result of the strict protection of the reserve. The period from the last detected major disturbance to the partial or complete death of the stand (currently) averaged 150 years. Judging by the taxation descriptions of 1939, in the stands of 17 out of 20 sample plots (85%), spruce dominated 70 years after a major disturbance (mainly after a fire), and later, over the next 80 years, the ratio of spruce and small-leaved tree species in the stand changed from 8 : 2 to 9 : 1. In the moss cover during this period, there was a change of dominants, namely, Polytrichum commune Hedw. to Sphagnum girgensohnii Russ. Over the 250-year history of the surveyed spruce massif, the uneven-aged structure of the forest stand was not achieved. 150 years after the last major violations, two main generations of spruce are distinguished in the age structure. Thus, on the southern border of the taiga zone, speaking about the stability of primary stands, we can only talk about the stable (continuous) existence of a spruce forest in this territory, which is determined by the possibility of its self-renewal. Currently, in the Central Forest Reserve, there are large areas of young spruce trees at the place of hurricane falls and areas of complete drying of the spruce stand. Such forests are the most fire-prone. Therefore, at the present stage of the dynamics of the spruce forests in the Central Forest Reserve, it is extremely important to protect the forest from fires.