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

Abstract

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.