Characteristics of the process of tree mortality occurring in the Polish Sudetes Mts

Abstract The forests of the Sudetes Mts are among the ecosystems most threatened by climate change in Poland. Abiotic factors cause the threat, such as an increase in the average annual temperature and a clear change in the distribution of atmospheric precipitation intensity during the year. The aim of the study is to characterise the process of tree mortality, especially spruce, the main forest-forming species of the region, in the Sudetes. The analyses carried out covered 12 forest districts belonging to the Regional Directorate of State Forests in Wrocław. Calculations made with the stand growth model showed that the total volume of merchantable timber in the forest districts is about 58 million m 3 , of which 68% consists of spruce. Two indices characterising the process of tree dieback, that is, tree dieback index (the volume of deadwood of a specific tree species harvested in the period 2011–2022) and tree dieback intensity coefficient (the quotient of the volume of deadwood harvested after the occurrence of the main cause of tree dieback and the volume of deadwood harvested before the occurrence of this cause there) were applied. The threat process intensified in 2015, when drought during the vegetation season caused massive thinning of trees and breakdown of tree stands, especially spruce stands and, to a lesser extent, pine and larch stands, and the least of all, birch, alder and beech stands. Therefore, it was assumed in the study that it is the ratio of the volume of deadwood obtained in the periods 2015–2018 and 2019–2022 to the volume of deadwood obtained in the period 2011–2014. There is an urgent need to change the concept of forest management in Poland. In the field of silviculture, it should include in particular: a) planning the species composition of tree stands, adapted to the changing of their growth conditions; b) a critical approach to the methods of forest management, including harvesting system and c) a critical verification of the methods used to determine the action level of cutting management, especially harvesting systems, and the order of selection of tree stands for the implementation of these treatments.