Change in plant spatial patterns and diversity along the successional gradient of Mediterranean grazing ecosystems

Abstract

In this study, we analyze the complexity of plant spatial patterns and diversity along a successional gradient resulting from grazing disturbance in four characteristic ecosystems of the Mediterranean region. Grazing disturbance include not only defoliation by animals, but also associated disturbances as animal trampling, soil compaction, and mineralization by deposition of urine and feces. The results show that woodland and dense matorral are more resistant to species loss than middle dense and scattered matorral, or grassland. Information fractal dimension declined as we moved from a dense to a discontinuous matorral, increasing as we moved to a more scattered matorral and a grassland. In all studied cases, the characteristic species of the natural vegetation declined in frequency and organization with grazing disturbance. Heliophyllous species and others with postrate or rosette twigs increased with grazing pressure, particularly in dense matorral. In the more degraded ecosystem, only species with well-adapted traits, e.g., buried buds or unpalatable qualities showed a clear increase with grazing. Indeed, the homogeneity of species distribution within the plant community declined monotonically with grazing impact. Conversely, the spatial organization of the characteristic plants of each community increased in the better-preserved areas, being also related to the sensitivity of the species to grazing impact. The degree of autocorrelation of plant spatial distribution at the species level and the information fractal dimension at the community level allow us to quantify the degree of degradation of natural communities and to determine the sensitivity of key species to disturbance.

Local facilitation, bistability and transitions in arid ecosystems

“…Vegetation patches of different sizes, shapes and spatial distributions have been observed in arid ecosystems throughout the world (e.g., Aguiar and Sala, 1999;Rietkerk et al, 2000;Alados et al, 2004;Webster and Maestre, 2004). These observations have raised questions about the origin of this patchiness and the mechanisms that maintain it.…”

Spatial vegetation patterns and imminent desertification in Mediterranean arid ecosystems

“…Their movement (located by Global Positioning System, GPS, and transferred to a map in a Geographic Information System) and the time spent in each site were recorded. Effective stocking rate was calculated as the average stocking rate multiplied by the percentage of time each grazing site was used 28 . Vegetation surveys were conducted in 2000 from April to June 28 .…”

“…Effective stocking rate was calculated as the average stocking rate multiplied by the percentage of time each grazing site was used 28 . Vegetation surveys were conducted in 2000 from April to June 28 . Transects were laid out, and the vegetation cover under the tape was recorded by measuring the starting and end points (in centimetres) of each species.…”

Overgrazing in the Montado? The need for monitoring grazing pressure at paddock scale

“…These variations of attractiveness of resources in space and time create a spatial mosaic pattern of animal distribution. The consequent uneven grazing will affect vegetation dynamics (Alados et al 2004) and can increase or decrease pasture spatial heterogeneity (Adler et al 2001).…”