Growth, tolerance and zinc and cadmium hyperaccumulation of Thlaspi caerulescens populations from three metal contaminated soils and three normal soils were compared under controlled conditions. Individuals of six populations were cultivated on five soils with increasing concentrations of zinc (50-25 000 µg g −" ) and cadmium (1-170 µg g −" ). There was no mortality of normal soil populations in the four metal-contaminated soils, but plant growth was reduced to half that of populations from metal-contaminated soils. However, in noncontaminated soil, the growth of individuals from normal soils was greater than that of individuals from metal-contaminated soils. Individuals from normal soils concentrated three times more zinc in the aboveground biomass than those from metal-contaminated soils, but the latter accumulated twice as much cadmium. We conclude that populations of T. caerulescens from both normal and metal-contaminated soils are interesting material for phytoextraction of zinc and cadmium, but to optimize the process of phytoextraction it is necessary to combine the extraction potentials of both type of populations.

Summary Recent, rapid and often underestimated landscape changes have occurred over large areas in Mediterranean Europe. They are the result of major rural depopulation. Old photographs of landscapes taken at the beginning of the twentieth century (i.e. old postcards) and present‐day photographs taken at the same places were compared in a 2500‐km2 area of southern France. Vegetation changes were analysed using transition matrices. During the 80‐year study period, land uses and vegetation changed dramatically. Woodland cover and tree height increased; but in contrast, the extent of cropped lands and rangelands decreased. Forest spread was heterogeneous, depending on initial composition of the vegetation, and locally dominant ecological and socio‐economic conditions. Our data show that a Mediterranean forest can re‐establish under humid climatic conditions and spread within a century, despite severe prior exploitation over several decades. These dramatic changes are liable to have biological and ecological consequences (e.g. spread of woodland species, threat against open habitat species, fire regime modification, deterioration in water resources), some of them being already perceptible.

Summary 1The downy oak Quercus humilis has recently recolonized the Causse du Larzac plateau in southern France. We studied the in¯uence of the shrubs Buxus sempervirens and Juniperus communis on Q. humilis establishment, and of Buxus on the growth of established Q. humilis individuals. 2 Percentage germination of experimentally planted Q. humilis was higher under shrubs than in nearby open areas and higher on the north than the south side of the canopy. Germination where part of the canopy has been removed was similar to that away from the shrubs, suggesting that the facilitation mechanism is related to changes in microclimate rather than to a soil e ect. 3 When exposed to sheep for 1 month, 100% of 326 unprotected oak seedlings were grazed, causing 44% mortality. The presence of Buxus and Juniperus improved seedling survival by protecting them against sheep grazing and summer drought. Predation by rodents was however greater under shrub cover. 4 The highest leaf dry mass of oak seedlings was recorded under Juniperus where light conditions seem more favourable for growth than under Buxus (direct e ect) or in grassland (indirect e ect). The growth of naturally established individuals of Q. humilis (in terms of total leaf mass per annual branch and width of rings) was lower under Buxus than in grassland but the values became similar once the canopy was overtopped. 5 The balance between positive and negative interactions varied in relation to the life stage of Q. humilis and the two shrub species. Regeneration of Q. humilis in open grassland was prevented by grazing. The protection o ered by shrubs continues to o set the negative interference on growth, particularly under Buxus, so that plants could survive to overtop the shrub canopy and reach maturity. The succession pathway therefore depends closely on the distribution of shrubs in the grassland.

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