- Spatial pattern in Anthyllis cytisoides shrubland on abandoned land - 627 Journal of Vegetation Science 8: 627-634, 1997 © IAVS; Opulus Press Uppsala. Printed in Sweden have different effects on plant water use, evapotranspi- ration and hydrology (Shuttleworth & Wallace 1985). Determination of the demography and patterns of sparse vegetation and the prediction of their development and possible change can therefore improve estimates of the hydrological balance of ecosystems (Wallace et al. 1990). In practice, however, such changes in the vegetative cover are rarely considered in models. Sparse vegetation is typical of large areas of aban- doned land in semi-arid southeastern Spain, which re- ceive a mean annual rainfall of 200 - 400 mm and have up to four months of summer drought. These lands, often fields of irregular shapes and poorly defined mar- gins depending on the local topography and soil texture, were formerly intermittently ploughed and sown with cereals. Arable cultivation ceased several decades ago and the ‘fields’ now support semi-natural shrublands (Puigdefábregas et al. 1996). These shrublands are pre- sumed to represent an intermediate stage of an old-field succession. Therefore, the floristic composition, stand density and the spatial distribution patterns of the shrubs are expected to change with time which will have conse- quences for the hydrological balance. As part of a wider research project (MEDALUS II - Mediterranean Desertification and Land Use) on the ecology of sparse vegetation and its effects on hydrology and soil erosion in a semi-arid environment, we investi- gated the trends of changes in plant density and distribu- tion pattern. Although the land was successively aban- doned and the present vegetation must therefore be a mosaic of different ages, the exact time of abandonment of particular fields is usually not known and information on the development of the vegetation must be obtained by other means. As a result of cultivation, the aban- doned fields provide spatially uniform habitats which offered, in addition to material for demographic studies, the possibility for analysis and ecological interpretation of the distribution patterns and spatial relationships of perennial plants. These were investigated by second- order spatial analysis based on Ripley’s K-function (Ripley 1976, 1981), a method which is able to detect Spatial pattern in Anthyllis cytisoides shrubland on abandoned land in southeastern Spain Haase, Peter * , Pugnaire, Francisco I. 1 , Clark, S.C. & Incoll, L.D. Department of Biology, University of Leeds, Leeds LS2 9JT, UK; 1 Present address: Estación Experimental de Zonas Áridas, General Segura 1, E-04001 Almería, Spain; * Author for correspondence; Dyckerhoffstrasse 3, D-49525 Lengerich, Germany; E-mail haasep@t-online.de Abstract. Univariate and bivariate distribution patterns of small shrubs on abandoned land in semi-arid southeastern Spain were investigated by second-order spatial analysis (Ripley’s K-function). All shrubs (Anthyllis cytisoides and subdominant Artemisia barrelieri) were either randomly dis- tributed or clumped at scales of 0.25 - 1.0 m. The pattern shown by A. cytisoides shrubs alone changed from clumped to random with decreasing density. Pattern analysis and demo- graphic data suggest a successive replacement of A. barrelieri, which had high proportions (44 - 86 %) of dead shrubs, by the dominant A. cytisoides. In two of three plots there was a positive association between A. cytisoides and A. barrelieri at a scale of 0.25 - 0.5 m. In the third plot, believed to represent a more advanced stage of colonization, there was a negative association (repulsion) between the two species, presumably as a result of interspecific competition from A. cytisoides. Dead shrubs present in spring 1994 were randomly distrib- uted in all plots. Living and dead A. cytisoides shrubs were positively associated at a scale of 0.5 m, suggesting that the shrubs died as a result of intraspecific competition in small clumps. The shrubland previously dominated by A. barrelieri is changing to A. cytisoides shrubland with increasing biomass and ground cover. Keywords: Artemisia barrelieri; Competition; Mediterra- nean shrubland; Old-field succession; Second-order spatial analysis; Semi-arid. Nomenclature: Sagredo (1987). Introduction Whenever an established vegetation is destroyed or disturbed, its recovery progresses through a sere of successional stages which may differ strongly in den- sity, physiognomy and taxonomy from the original veg- etation (e.g. Wood & del Moral 1988; Chapin et al. 1994). Changes in the density and physiognomy of the vegetation have strong effects on hydrology and soil erosion, particularly in arid and semi-arid environments. Here, in the usually sparse vegetation, different spatial distribution patterns of equal densities of plants can