The evolution and significance of soil-vegetation patterns following land abandonment and fire in Spain

Examples are presented from two locations in SE and NE Spain where patterned or banded vegetation are found on semi-natural and abandoned land or where vegetation is recovering from wildfire. In both cases patterns are being investigated as process-pattern phenomena with the aim of understanding how different kinds of environmental gradients influence pattern evolution. On abandoned land, patterns occur at different scales. At the patch scale there are areas where Plantago albicans germinates in cracks and influences the accumulation of silty material, At the slope scale these form elongated steps that create a characteristic micro-topography, At the patch and slope scale Stipa tenacissima tussocks form an hexagonal pattern on level areas where water infiltrates in and around the tussocks, On sloping areas the S, tenacissima tussocks form parallel ovoid bands. They intercept fine and coarse material being eroded on the slopes by both overland flow and the hooves of sheep and goats. This also creates a distinctive micro-topography. Rainfall simulation experiments were undertaken in combination with monitoring activities in order to investigate the effects that key-processes of sediment and water movement have on the patterns. Other methods include controlled experiments and modelling. Biologically driven erosion processes are very important as key processes. Positive feedback mechanisms are important at various stages in the evolution of the pattern. The patterns studied play an important role in creating more favourable micro-environments where vegetation recovers first after disturbances, This is particularly the case following wildfire. The first post-fire rain produces patterns in ash and litter around sites, concentrating these at locations where shrubby vegetation subsequently resprouts or becomes seeded. On abandoned land. the evolution of patterns reflects the parent material, grazing and the climate. (C) 1999 Elsevier Science B.V. All rights reserved.