Environmental controls on species composition along a (maquis) shrubland to forest gradient on ultramafics at Mont Do, New Caledonia
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The landscape-scale pattern of distribution of maquis, maquis with emergent conifers (Arauacaria laubenfelsii), and rain forest, on ultramafic substrate at Mont Do, New Caledonia, is investigated in relation to soil and plant chemistry, light and moisture. The structure and composition of these vegetation types reflects the impacts of disturbance on the one hand, and of physiological stresses on the other. Disturbance by fire is important in determining the presence and abundance of maquis and rain forest at the landscape level and is discussed in detail by Perry et al. elsewhere in this issue. The impacts of light environments, water availability and soil chemistry on the succession of vegetation from maquis to forest are also important. The chemistry of iron-crust and eroded oxisol soils does not vary greatly between vegetation types, and does not appear to define the distribution of species at the local scale. Nevertheless, low concentrations of macronutrients (such as P) and slow rates of biomass accumulation associated with this ultramafic landscape may be important in slowing the rate of progression of the vegetation from maquis to forest. Chlorophyll fluorescence studies of seedlings, saplings and trees in macquis and forest provide strong evidence for severe reductions in photosynthetic efficiency in photosystem II on clear days for seedlings growing in maquis. The importance of increased water supply to plants establishing beneath emergent araucarians in maquis through cloud-combing is also illustrated.