Correlation of Habitat and Structural Factors with Dieback and Nutrition of Silver Fir (Abies alba Mill.) in Gorski Kotar

Dieback of silver fir in Croatia, especially in the Dinaric part, is associated with complex changeable effects of abiotic and biotic factors. In industrial forests, the volume of dieback trees or volume of trees cut down in salvage cutting is most often used for showing tree dieback intensity, and can be used as an indicator of forest stand health status (Capecki 1981).The aim of this research was to show the correlation of silver fir dieback with habitat and structural factors, calculate the intensity of dieback according to volume, and determine tree dieback dynamics and effects of habitat factors on concentration of essential mineral nutritive elements in needles and soil.The research was carried out in the mountainous part of Croatia, in beech-fir and fir forests of Gorski Kotar. The research included the forest stands of disrupted stability and structure, at the border of the natural range of sliver fir towards a warmer area and optimum area of silver fir i.e. central part of Gorski Kotar. Data for wood mass of dieback silver fir trees were collected for the selected management units at the level of all compartments and subcompartments in the management unit. The data were being collected for twelve years (1995–2007). In the researched area, needle sampling from tree crowns was carried out on trees with three different levels of defoliation (<25%, 25–60%, >60%). Dry needle mass was determined as well as concentration of K, Ca and Mg. Soil chemical analysis included soil reaction, and amount of phosphorus (P) and potassium (K) in the soil.The average annual silver fir dieback intensity for forest stands at the border of the natural range was 18.3 m3/ha or 9.2% of silver fir growing stock, and in forest stands in the central part of Gorski Kotar it was 6.2 m3/ha or 4.1%.The maximum annual dieback intensity in forest stands at the border of the natural range was 113.0 m3/ha, and in forest stands in the central part of Gorski Kotar it was 55.4 m3/ha. For forest stands with recorded dieback, the average annual increment was 2.7 m3/ha, and in forest stands in the central part of Gorski Kotar it was 3.3 m3/ha. In forest stands with sliver fir dieback, dieback intensity was higher than the value of the growing stock (Table 1).Intensity of the average annual silver fir dieback at the border of the natural range was from 1.6 to 18.8 m3/ha, and in forest stands in the central part of Gorski Kotar from 5.0 to 7.5 m3/ha (Fig. 1).In forest stands at the border of the natural range, the highest average annual silver fir dieback intensity was recorded in silver fi