INTERSPECIES COMPARISONS OF THROUGHFALL AND STEMFLOW AT 3 SITES IN NORTHERN BRITAIN

Rainfall, throughfall and stemflow were collected every 2 weeks for 2 years at three forest sites in northern Britain. At each site, the distribution of water under pine (Pinus sylvestris L.) was compared with that under one or more other species, including Norway spruce (Picea abies (L.) Karst), Sitka spruce (Picea sitchensis (Bong.) Carr), larch (Larix decidua L.), oak (Quercus petraea Matt.) and alder (Alnus glutinosa (L.) Gaerta). Throughfall and stemflow amounts were strongly correlated with rainfall for all species and sites. Throughfall was a variable proportion of rainfall between years and between seasons. The annual proportions for Scots pine were in the range 51-78% at the three sites, for larch the range was 73-87% at two sites, for spruce 63-71% at two sites, and for broadleaved species 72-75% at one site. There was no obvious seasonal pattern, even for deciduous trees. Proportions of stemflow were consistent between seasons and years for a given site and species, in the range 6-15% for Scots pine at the three sites, 1-4% for larch at two sites, 13-14% for spruce at two sites, and 9-10% for the broadleaved species at one site. Interception loss, calculated as the difference between measured rainfall and (throughfall + stemflow) showed little seasonal variation for any species when expressed as a proportion of rainfall. At one site, there was evidence of significant capture of cloud and/or fine rain by the spruce canopy, resulting in an apparent small interception loss. Attention is drawn to the systematic errors which can arise through the neglect of occult deposition when calculating interception loss at upland sites.