The dynamics of vegetative and reproductive growth were compared in matched pairs of Mediteranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Brachypodium distachyon (L.) Beauv. and Bromus fasciculatus C. Presl., under high and low levels of water availability in a common-environment experiment. Plants of all desert populations showed earlier switches to reproductive development and to subsequent phenophases, and the transition to flowering occurred at smaller plant sizes. Water stress had no effect (E. hispanica) or slightly accelerated the transition to flowering in B. fasciculatus (by 1-2 days) and in B. distachyon (by 4-6 days). Plant senescence was strongly enhanced by water stress, and this enhancement was greater in desert populations than in corresponding Mediterranean ones. Duration of life cycle was greatly shortened by water stress in all three species. Desert and Mediterranean populations of the three species exhibited small differences in their relative response, i.e. phenotypic plasticity, to water stress for phenological and plant size parameters. In E. hispanica and B. fasciculatus the population x water regime interaction amounted to less than 3% of total variance. By contrast, the Mediterranean population of B. distachyon was much more plastic in its response to water stress than the desert population in its transition to plant senescence. Plants from the desert populations appeared to be adapted to shorter, more compact growth cycles, culminating in earlier dates of seed maturation and plant senescence. In addition, they showed larger phenotypic plasticity in the transition to plant senescence, which trait was enhanced or magnified by sustained or repeated lack of water. By contrast, plants from Mediterranean populations delayed switchover from one phenophase to the next, seeming thus to "bet" on more water being forthcoming.

Reproductive effort (relative allocation of biomass to diaspore production) was compared in matched pairs of Mediterranean and desert populations of three unrelated annual species, Erucaria hispanica (L.) Druce, Bromus fasciculatus C. Presl. and Brachypodium distachyon (L.) Beauv., grown under high and low levels of water availability in a common-environment experiment. Desert populations in all three species showed higher reproductive effort than corresponding Mediterranean populations, as expressed by both a reproductive index (RI= reproductive biomass/vegetative biomass), and a reproductive efficiency index (REI=number of diaspores/total plant biomass). Moreover, in E. hispanica and Brachypodium distachyon, inter-populational differences in reproductive effort were greater under water stress, the main limiting factor for plant growth in the desert. These results indicate that variability in reproductive effort in response to drought is a critical and dynamic component of life history strategies in annual species in heterogeneous, unpredictable xeric environments. When subjected to water stress the Mediterranean populations of E. hispanica and B. distachyon showed greater plasticity (e.g. had a greater reduction) in reproductive effort than the desert populations, while in Bromus fasciculatus both populations showed similar amounts of plasticity.

There are only five mediterranean-climate regions (MCRs) on Earth-the Mediterranean Basin, most of California, central Chile, southern South Africa, and south-central and southwestern Australia. They all have cool, or cold, and relatively wet winters alternating with long, hot, and dry summers. Spring and autumn seasons are ephemeral in comparison, and highly variable. During much of the year, droughts lasting weeks or even months are frequent, with grave consequences on all biota, since water is the key limiting factor for growth and well-being of all organisms, including humans. Yet, biodiversity is unusually high in all five MCRs. Well adapted woodlands and shrublands, which are the subject of this chapter, are numerous and noteworthy, in ecological, cultural, and socioeconomic terms. Climate, geology, and evolutionary biogeography of MCRs have all contributed to alpha, beta, and gamma biodiversity of these regions. In the Mediterranean Basin, California, and Chile, the predominantly young, orogenic systems produce intense geomorphologic dynamics with poorly developed, shallow soils (Bradbury 1981). The uneven relief with steep slopes in large parts of the territory and spreading of unconsolidated and soft substrata increase the risk of soil degradation. In sharp contrast, MCR landscapes in South Africa and Australia are ancient and stable; as a result, they have highly weathered and leached soils that are very poor in nutrients (Rundel 1998). Human land use histories have also contributed to ecological diversity in all five regions, and must be taken into account when contemplating or undertaking ecological restoration. Natural wildfires are common in most of the five MCRs, owing to the high accumulation of fuels leading to enhanced flammability in summer, the frequency of lightning storms and, in some areas, periodic but intense, hot and dry winds such as the Santa Ana in California, and the Mistral in southern France. An exception is central Chile where the Andean Cordillera protects the MCR area from summer storms and lightning (Rundel 1998). As a result, central Chilean sclerophyllous vegetation is ill-adapted to frequent fires, never having had selective pressure from this form of disturbance over evolutionary time. Nonetheless, in recent decades anthropogenic fires have become much more common, and this is causing profound changes in the characteristic features of central Chilean landscapes (Armesto et al. 2009). In spite of the similarities in climate, many striking differences can be found among MCRs, in addition to fire regime. As mentioned, historical differences in land use practices, including the time span of degradation processes, socioeconomic dependence on local resources, and cultural perceptions of the relationship between humans and nature all have great impact on biota and ecosystem dynamics. The Mediterranean Basin is the only MCR in the so-called Old World, where humans have practised agriculture for as long as 13 millennia, in some areas (Purugganan & Fuller 2009). The process, initiate...

No abstract