THE INTERCEPTION, THROUGHFALL AND STEMFLOW IN A FOREST IN HIGHLAND SCOTLAND AND THE COMPARISON WITH OTHER UPLAND FORESTS IN THE UK

Interception loss from a 50-year-old Sitka spruce forest at Balquhidder in Highland Scotland has been determined by measuring precipitation, throughfall and stemflow. Annual mean precipitation at the site was 2130mm and for the period October 1983 to June 1986, the average interception was 28% with throughfall and stemflow comprising 69 and 3%, respectively of the precipitation. This interception loss is similar to results from other upland forests in the U.K. While large variations were found throughout the year, interception was greatest in the summer months, reaching 79% in May 1985, and least in the winter, 0% in January 1985. Snow interception can be large, 37% in January 1984 when storage on the canopy was estimated to have reached 22mm water equivalent. The spatial variability of throughfall was dependent on distance away from the tree stem and on the density of the canopy cover. Tree age does not appear to determine interception values but comparison of the relative amounts of throughfall and stemflow with those from other sites shows that there is an increase in throughfall with the age of the tree. This has important consequences for water quality in young forests. © 1990.