Patterns of structural complexity and human disturbance of riparian vegetation in agricultural landscapes of a Mediterranean area

Riparian corridors are valuable high diversity habitats in Mediterranean-type environments and mainly in agricultural landscapes. Following a ‘vegetation complexes’ approach along fluvial landscapes, the factors affecting structural complexity and human disturbance through agricultural areas in south-west (SW) Spain were analysed. Using principal component analysis and a stepwise multiple regression analysis three main results were obtained: (1) a successional vegetative gradient was noted from upper (pioneer herbaceous communities) to lower reaches of streams (closed-canopy forests) with a concomitant increase in both woody cover and habitat diversity; (2) land-use intensity associated with each of the agricultural production methods, which was mainly related to topographic irregularity, appeared to be the main cause of human disturbance in riparian areas. Thus, the closed-canopy forests located in flat landscapes of lower streams were removed, highly modified or extensively fragmented; in contrast, riparian complexes placed on wild and rough landscapes of upper streams appeared as undisturbed or near-natural; (3) nearly 50% of the natural riparian vegetation of the study area has been highly modified or has disappeared, in most cases replaced by non-natural formations which have today become dominant. The protection of the few existing well-preserved riparian corridors and the restoration of highly altered riparian areas in the lower reaches of streams has become a priority in maintaining biodiversity in these agricultural Mediterranean landscapes. The extensive and cost-effective method developed for this study would be easily applicable to other large areas to evaluate the effect of human disturbance on riparian corridors