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

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.http://www.sciencedirect.com/science/article/B6VBS-4D2FMJK-3/1/3bd96d3eb6d9aa73038f87bb6b8c82b

Assessment of grazing effects on mediterranean shrubs Phillyrea latifolia L. and Cistus monspeliensis L. with developmental instability and fractal dimension

In this study we used developmental instability expressed as translational and fluctuating asymmetries as well as fractal dimension in order to assess the effects of different levels of grazing pressure by goats on two dominant species of Mediterranean shrublands, i.e. Phillyrea latifolia L., a palatable, and Cistus monspeliensis L., an unpalatable shrub. Treatments included light, moderate and heavy grazing pressure. For the former species, an additional ungrazed treatment was used as a control. Measurements were carried out in thirty shrubs of each species in each treatment. For Phillyrea, the fluctuating asymmetry analysis revealed higher asymmetry of leaves in the grazed treatments than in the control. The lower parts (below 1.5m height) of Phillyrea shrubs, reached by goats, also attained larger values of asymmetry in comparison to the upper parts (above 1.5m height) of the shrubs, not reached by goats. Moreover, fractal dimension of branches was lower in the grazed treatments in comparison to the ungrazed ones, as well as in the lower parts compared to the upper parts of the shrubs. However, the results of translational asymmetry analysis showed that grazed shrubs were developmentally more stable than the ungrazed ones. These results suggest that Phillyrea is very tolerant to grazing; its upper part can be maintained in a non - stressful situation even when its lower part is overgrazed. For Cistus, the results of translational asymmetry revealed that grazing did not affect its developmental stability. The effects of grazing on fractal dimension declined under moderate grazing situations. This indicates that Cistus is developmentally stable both in well preserved and in heavily disturbed sites. It is concluded that developmental instability and fractal dimension are useful tools in assessing the differential response of Mediterranean key species to grazing impact.This research is part of the INCO project DRASME ( Desertification Risk Assessment in Silvopastoral Mediterranean Ecosystems, contract no. IC18- CT98-039), financed by the European Commission. Greece-Spain Bilateral Action No 200GR0001 also supported the project. The support from both these projects is gratefully acknowledged.Peer reviewe