Tenacissima Tussocks Research Articles

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.

Response of the Tussock Grass Stipa tenacissima to Watering in a Semi-Arid Environment

1. Stipa tenacissima is a perennial tussock grass of arid and semi-arid zones around the Mediterranean basin that occupies extensive areas in south-eastern Spain. The environment of this region is extreme, with low irregular rainfall, high temperature and high irradiance, so that S. tenacissima tussocks are subjected to a high degree of environmental stress, especially during the summer months. 2. The ability of S. tenacissima to use a pulse of water applied in midsummer was tested in a field experiment in which extension growth and physiological performance of leaves of watered and unwatered plants were measured. 3. In unwatered plants, when leaf extension had ceased, leaf water potential, relative water content, leaf conductance and net photosynthetic rate were low and minimum fluorescence was high. 4. Leaf conductance and net photosynthetic rate doubled, leaf extension resumed, minimum fluorescence (F 0 ) fell and photosynthetic efficiency of photosystem II (F v /F m ) rose with watering. As the soil dried out again, values of these variables approached or equalled those of unwatered plants. 5. These changes in F 0 and F V /F m suggested that the photosynthetic apparatus had not been damaged permanently, i.e. that S. tenacissima has reversible photoprotective mechanisms. 6. We conclude that the decreased photosynthetic rate of unwatered plants in summer results from non-damaging photoinhibition and low leaf conductance. The latter is partly a consequence of the folding of leaves, which was inversely proportional to relative water content. 7. The arrested development of S. tenacissima leaves was apparently not due to summer dormancy because leaves responded opportunistically within days to an applied pulse of water.