Relationships between precipitation, stemflow and throughfall for a lowland beech plantation, Black Wood, Hampshire, southern England: findings on interception at a forest edge and the effects of storm damage

Abstract

Precipitation (rainfall plus snowfall), throughfall (canopy and free throughfall), stemflow and net precipitation (stemflow plus throughfall) data are presented for a network of collectors located in a fully developed lowland beech plantation. Precipitation averaged 640 mm year −1 and conditions were relatively dry during the sampling period: the long-term average precipitation is about 800 mm year −1. Stemflow constitutes on average 5% of the net precipitation and it varies according to season: from 1–2% during the leafed to 6–16% during the dormant winter period. The interception loss (the difference between precipitation and the net precipitation) averages about 14–16% and varies to a limited degree through the year. The values are highly scattered but there are lower values for the first few months of each year: for January–March 1991 negative interception losses were recorded. These very low values appear to be associated with inputs other than precipitation (such as mist, dew, fog and ice) or snow, or a combination of the two; the water inputs to the catchment may well be underestimated at this time. Edge effects, if they exist, occur at less than 20 m from the edge and so are of little importance in relation to water resources. Storm damage and associated tree loss reduced interception loss although the effect is not as great as might have been expected: the loss of canopy is compensated in part by an increased roughness that in turn increases turbulence and hence interception losses. It is concluded that (1) the precipitation measurements provide the weakest link in estimating interception losses and (2) the network design used in this study is adequate for determining the spatial and temporal variation in net precipitation.