Chapter 1 - Núria BONADA

Regional amd local scale: convergences and divergences
In the mediterranean climate areas, the water high seasonal stress condition implies that
organisms present some specific adaptations. Consequently, most of the affinities it can be
found between these areas are related to physiological, morphological or behavioral
adaptations (e.g. in artropods —Stamou, 1998) to avoid the severity of drought and its
seasonality and interannual variability. In that sense, resilience and resistance are common
attributes found in the elements of the mediterranean biota (Grubb & Hopkings, 1986), being
the first more frequent (Fox & Fox, 1986). These adaptations give higher probability of
permanence to mediterranean communities to the seasonal predictable natural disturbances
(Aschmann, 1973; Orshan, 1983).
In addition to this harsh natural conditions, mediterranean climate areas have been exposed
since many years ago to human disturbances (Mooney, 1982), although the human impact
differs among med-regions because of the different time of human colonization (Aschmann,
1973b; Fox & Fox, 1986). Probably, fire is the main disturbance in these ecosystems (Miller,
1983; Keely, 1986), altering nutrient availability and influencing on speciation (Cowling, 1987)
with fire-dependents and resilient plants (Kruger, 1979ac; Fox & Fox, 1986; Keely, 1986). For
instance, in the South African fynbos several plants need the fire to reproduce; in Australia
some tree are adapted to fire and its frequency and intensity; and even in Chile with a weak
fire history, some adaptations to fire are present (Grove & Rackham, 2001).
Trabaud (1981) points out that med-regions are unique to have been affected by human
activities for ages, as the introduction of non-native plants and animals, agriculture, cattle,
urbanization, salinization... (Conacher & Sala, 1998). Because of the impact of all these
activities, med-regions are characterized by lost of natural vegetation, soil salinization, water
pollution and high erosion (Conacher & Sala, 1998). These consequences can be more or less
important in each region, and topography, lithology or the climate itself can accelerate the
erosion and the land degradation (see Conacher & Sala, 1998). Hence, an increase of
temperature by climate change could have important consequences in the mediterranean
ecosystems, enhancing the water stress in the arid and semiarid areas or prolonging the
growth season in the alpine regions (Le Houérou, 1990).
Mediterranean rivers
Rivers influenced by this climatic heterogeneity in temperature and precipitation regimes are
considered mediterranean rivers (Gasith & Resh, 1999). Because in the mediterranean climate
several microclimates can be distinguished (Nahal, 1981; Daget et al., 1988), we understand
that several river typologies can also distinguish in med-regions: from mountain permanent
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