Effects of forest age, structure and dominant species (spruce and Swiss stone pine) on water balance in the Tyrolean Alps

Subalpine forests in the Alps are vulnerable ecosystems and valuable supplies of water for environment. Coniferous forests are sensitive to climate changes and human interventions. Although several water balance components have been assessed in earlier research, nothing is known about the frequency and impact of fog on the water balance. This article presents the results of the investigation carried out in subalpine coniferous forests of northern Italy. The aim is to determine the hydrological balance of the area and evaluate the significance of fog occurrence in forests dominated by spruce (Picea abies) and Swiss stone pines (Pinus cembra), as well as Scots pine (Pinus sylvestris L.) and European rowan (Sorbus aucuparia). Methods include water outflow, fog interception, and eddy covariance (EC) techniques for measuring evapotranspiration. The workflow included operation with tree transpiration sensors, phonecam pictures, throughfall and stemflow gauges, water discharge measurements, soil moisture sensors, and epiphyte quantification. These methods were used to monitor dense, old-growth coniferous forest (>200 years old trees) as well as young trees (< 30 years). The study has shown that fog plays a significant influence on the water balance of temperate, coniferous mountain forests. Besides, precipitation interception and evapotranspiration partitioning vary with forest age.