10
Introduction
characterised by an increased proportion of plants with seasonally dimorphic leaves as well as plants with spines, and by a lesser proportion of plants
with succulent leaves, while they are the. only systems in which plants without leaves as well as species deciduous in winter have been recorded. Diamantopoulos et al. (1994) postulated that these differences might partly be
attributed to climatic variations and partly to intensive exploitation (includinging frequent fires and grazing), which has existed for millennia in the
Mediterranean basin. Species diversity of woody plants can also be associated with management history. Comparatively less species diversity has been
recorded in the communities of Greek woody plants, this being attributable
to the selective pressure of intensive grazing. Apparently, the increased proportion of Labiatae species in Greek phrygana not consumed by grazing animals add support to this assumption.
The releves from Greek formations were ordinated on a CCA biplot
(Fig 1.7) along the first axis in relation to their bioclimatic origin. Samples
from the Aegean islands and from continental sites were ordinated separately. Moreover, the ordination of species and releves along the first axis is correlated primarily with soil variables (loss upon ignition, total-N and C/N
ratio), whereas short-term differences in the values of climatic variables are
not distinguishing factors. It seems that the distribution of phryganic formations on a major national scale is controlled by more stable characteristics
such as bioclimatic type and soil properties.
The two sets of Aegean and continental rei eves were treated separately.
Ordination of the Aegean samples was controlled by variables concerning
humidity conditions, whereas ordination of the continental samples was in
accordance with their geographical origin. In the latter case, samples from
the wettest western sites occupy the left endpoint of the axis, and samples
from the more arid eastern sites are ordinated closer to the right endpoint of
the axis. Similar biplots were obtained in cases where, instead of species composition, the dependent variable concerned life forms. It seems that within
smaller bioclimatic scales, local differences in climatic variables appear so
pronounced as to determine the ordination of samples on the CCA biplots.
The overall conclusion drawn by Diamantopoulos et al. (1994) is that longand short-term climatic effects, soil properties and anthropogenic factors are
synergetically, although not equally, involved in the establishment and
appearance of xeric Mediterranean ecosystems. In some areas these formations correspond to climax stages, while in others they are man-made.
1.2.4
The Resilience of Mediterranean-Type Ecosystems
The spatial heterogeneity of Mediterranean habitats originates from the heterogeneity of the Mediterranean landscape as well as from management practices involving overgrazing of the land coupled with frequent fires and the
Introduction
characterised by an increased proportion of plants with seasonally dimorphic leaves as well as plants with spines, and by a lesser proportion of plants
with succulent leaves, while they are the. only systems in which plants without leaves as well as species deciduous in winter have been recorded. Diamantopoulos et al. (1994) postulated that these differences might partly be
attributed to climatic variations and partly to intensive exploitation (includinging frequent fires and grazing), which has existed for millennia in the
Mediterranean basin. Species diversity of woody plants can also be associated with management history. Comparatively less species diversity has been
recorded in the communities of Greek woody plants, this being attributable
to the selective pressure of intensive grazing. Apparently, the increased proportion of Labiatae species in Greek phrygana not consumed by grazing animals add support to this assumption.
The releves from Greek formations were ordinated on a CCA biplot
(Fig 1.7) along the first axis in relation to their bioclimatic origin. Samples
from the Aegean islands and from continental sites were ordinated separately. Moreover, the ordination of species and releves along the first axis is correlated primarily with soil variables (loss upon ignition, total-N and C/N
ratio), whereas short-term differences in the values of climatic variables are
not distinguishing factors. It seems that the distribution of phryganic formations on a major national scale is controlled by more stable characteristics
such as bioclimatic type and soil properties.
The two sets of Aegean and continental rei eves were treated separately.
Ordination of the Aegean samples was controlled by variables concerning
humidity conditions, whereas ordination of the continental samples was in
accordance with their geographical origin. In the latter case, samples from
the wettest western sites occupy the left endpoint of the axis, and samples
from the more arid eastern sites are ordinated closer to the right endpoint of
the axis. Similar biplots were obtained in cases where, instead of species composition, the dependent variable concerned life forms. It seems that within
smaller bioclimatic scales, local differences in climatic variables appear so
pronounced as to determine the ordination of samples on the CCA biplots.
The overall conclusion drawn by Diamantopoulos et al. (1994) is that longand short-term climatic effects, soil properties and anthropogenic factors are
synergetically, although not equally, involved in the establishment and
appearance of xeric Mediterranean ecosystems. In some areas these formations correspond to climax stages, while in others they are man-made.
1.2.4
The Resilience of Mediterranean-Type Ecosystems
The spatial heterogeneity of Mediterranean habitats originates from the heterogeneity of the Mediterranean landscape as well as from management practices involving overgrazing of the land coupled with frequent fires and the