Utjecaj stanišnih promjena i načina gospodarenja na sušenje obične smreke (Picea abies Karst.) u Hrvatskoj | The impact of Site Changes and Management Methods on Dieback of Common Spruce (Picea abies Karst.) in Croatia

Common spruce (Picea abies Karst.) is a tree species that occurs naturally in the valleys and other frost sites in high mountain regions, where it is free of serious competition of other tree species. Being resistant to frost, the winter colds of the continental and mountainous climate suit it. It is highly tolerant of winter chills of the continental and mountainous climate, it likes areas with abundant precipitation and snow in particular and avoids those with little precipitation and low relative air humidity. In Croatia, it naturally occurs in high mountain areas of Gorski Kotar, Velebit and other parts of Lika, and especially in frost spots where it is free of competition with other tree species. In Europe, spruce is a favourite tree species for the establishment of forest cultures. It has the properties of both pioneer and transitional tree species. It is highly sensitive to summer droughts. During its growth, in its habitats it creates the conditions for the development of tree species of a climatogenous forest. It develops in regular and uneven-aged stands, while its percentage in selection stands with stable structural and stand conditions is lower. The total growing stock amounts to 13,200,000 m³, which accounts for 5.57 m³/ha of the forested area in Croatia. Its volume share in the highest age and diameter classes is 80%, which indicates its advanced age and physiological weakening. Regular and uneven-aged spruce forests of high silvicultural form cover an area of 6,300 ha, of which spruce accounts for 52% in the composition mixture, silver fir for 35%, common beech for 11%, and other species for 2%. Spruce is currently significantly affected by dieback; at the level of Croatia, the percentage of defoliated crowns is 59.3%, while in the Gorski Kotar area alone it is 96.2%. Droughts are one of the most important factors contributing to the physiological weakening and dieback of spruce in Croatia, while in Europe they are the major cause of dieback of catastrophic proportions. Temperatures measured in the past 15 years are the highest in the 150-year period, with a linear trend of temperature increase amounting to 0.74 °C. There is controversy as to the causes of droughts: according to many, they are the consequence of global warming, whereas others disagree.