Influence of soil properties on silver fir (Abies alba Mill.) growth in the Dinaric Mountains

Tree growth can be influenced by a wide variety of complex interacting factors. The contribution of soil to site productivity is confounded by the interactions between other site factors and silviculture. The contribution of soil properties to the growth of silver fir (Abies alba Mill.) was studied in the Dinaric Mountains, which are characterised by abundant sinkholes and limestone outcrops, resulting in diverse micro topography and different soil development at small spatial scales. Basal area increment and height growth data were estimated based on stem analysis of dominant silver fir trees (n = 65) on a 50 m × 50 m sampling grid, and competition intensity was determined. The soil development around each tree was defined using morphological properties of the genetic horizons based on soil probing (n = 65 × 12). In the study area, the chemical and physical soil characteristics (based on 21 soil profiles) were favourable for plant growth. Soil parameters e.g. soil depth, thickness of genetic soil horizons, share of soil types around each tree and soil associations were the factors controlling tree growth. Tree age and competition intensity were also influential factors in the case of height and radial tree growth respectively. Positive effects on height and radial growth were confirmed also for available water capacity of soil and location of tree in slope position (in the sinkhole, out of the sinkhole). The decrease in specific basal area increment with increasing competition intensity was most evident for trees growing on leached soils. The coefficient of determination and the statistical significance of the relationship between height growth and soil association over the last 100 years emphasised the cumulative effect of the soil condition on tree height growth.