F. Belmonte Serrato

A simple technique for measuring rainfall interception by small shrub: ''interception flow collection box''

Abstract: In this paper a simple technique for field measurement of rain water loss arising from interception and waterflows associated with species of small Mediterranean shrub is described: the ‘interception flow collection box’.This technique solves the problem of installing devices to control stemflow in species with a multiple trunk anddemonstrates its e†ciency through the results obtained from the data observed for three species of semi-aridMediterranean shrub: Juniperus oxycedrus, Rosmarinus o†cinalis and Thymus vulgaris. Finally, the empiricalequations for the prediction of throughfall, stemflow and rain water loss through interception are presentedfor the three selected species and the validity of the technique employed is established. #1998 John Wiley S drainage; stemflow; interception; small shrub INTRODUCTION AND OBJECTIVESInitial studies of interception arose from the idea that large areas of forest retain and evaporate a significantpart of the rainfall they receive, at the same time reducing the water resources available to the forest floor.These studies, essential to the research of water balance in wooded areas, are very important at a local andregional level, in addition to contributing to knowledge of the processes in a wide range of structurallycomplex forest covers.Following the initial work of Horton (1919), hundreds of experiments have been carried out in this area(for example, Haynes, 1940; Kittredge et al., 1941; Law, 1957; Rutter, 1963; Helvey and Patric, 1965;Leonard, 1966; Gash and Morton, 1978). However, the majority of these have been carried out in forests,with very few paying attention to other types of plant cover, such as shrubland, grassland, etc. (Burgy andPomeroy, 1958; Slatyer, 1965; Crouse et al., 1966; De Ploey, 1982; Tromble, 1988; Navar and Bryan, 1990).In forests, the procedures used to measure the water that passes through the cover and reaches the soil(throughfall) are various: ranging from a dense networkof pluviometers uniformly distributed around atree(Ford and Deans, 1978; Durocher, 1990; Belmonte Serrato and Romero Di´az, 1992), to a network ofpluviometers that are moved periodically (Aussenac, 1970) or maintained in their original, randomly chosenpositions (Veneklaas and Van Ek, 1990). Also, large surface pluviometers (Rutter et al., 1971; Massman,1983; Mulder, 1985) or ‘net rain water pluviometers’ (Calder and Rosier, 1976) have been used, althoughtheselatterdevicespresenttheproblemofsummingtheflowsofthroughfallandstemflow(waterthatreaches