A. Romero Díaz

Topographic control of soil moisture, vegetation cover and land degradation in a moisture stressed mediterranean environment

Abstract An erosion-vegetation competition model (THORNES 1985) assumes that surface litter, soil organic matter and soil moisture are positively correlated and that these in turn are correlated with topographic conditions on a uniform soil in a moisture-stressed environment. These relationships are tested for an experimental site in Mediterranean Spain. The results show that while these relationships are statistically significant, but rather weak, when all the data are used or when they are grouped according to geomorphic position (interfluve, hollow or slope), the correlations become stronger when considered in relationship to transects and when the data are subject to a low level of spatial smoothing. Even then, the relationships are rather complex, reflecting local features, the stage of vegetal development and, perhaps, the status of competition between erosion and vegetation.

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