The impact of drying on the thinning of spruce stands and on changes in the species composition of forest in the Perm Krai

The phenomenon of a massive drying out of spruce stands, which has been taking place in recent decades in our country and in other countries of the world, has many negative consequences: reduction of the area of forests acting as a carbon sink, inability of forests to perform their protective, environment-forming, water-protecting functions, and loss of habitat. A massive drying out of spruce stands can lead to changes in forest composition, significant thinning of spruce stands, and the change of the species. The focus of our research was on spruce forests in the southern part of the Perm Krai, specifically within the Oktyabrsky and Tchaikovsky forestries. 52 forest stands had been examined within our study area, primarily focusing on spruce forests of the wood sorrel and linden forest types, in the summer periods of 2017-2024. As a result of the study in the above years, it was found that in terms of sanitary condition, the predominant species of spruce stands are spruce stands that are dying out, their share exceeding 50 %. Additionally, around 17.3% of the surveyed stands were found dead. The calculated coefficient of variation indicates that the variability of the average weighted scores of the sanitary condition increases with the age of spruce stands in plantations of both studied forest types. The dependence of variability of weighted average sanitary condition scores on the age of the stands is described by a polynomial function. On average, 30.7 to 47.3% of spruce trees survive after drying out in plantations of both types of forest. The species composition of plantations changed in 75% of cases as a result of drying out. The predominant stands are those where the share of spruce in the composition of stands has decreased by 10 %. In a number of cases there is a change from native spruce stands to soft stands. At the same time, the share of stands in which the drying out process led to the complete death of spruce trees is 5.8%. As a result of the density study, it has established that the drying out of some spruce trees led to the formation of spruce stands of low density and sparse forests.