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Free keywords:
pioneer; varzea; establishment strategy; Cecropia latiloba; Senna reticulata; Amazonian floodplain
Abstract:
Two pioneer woody plant species with differential growth habits, Cecropia latiloba and Senna reticulata, form monospecific stands during secondary succession in Amazonian floodplains. The 'fugitive strategy' of Cecropia latiloba enables vertical evasion from competition by continuous height growth without branching. This establishment strategy is aided by high submergence tolerance. In contrast to this, the 'possessive' Senna reticulata shows fast height growth only in the first non-flooded period, with extreme lateral branching and effective shading of competitors. This strategy is efficient only on higher elevations in the flooding gradient where complete submergence does not occur and on sites with supposedly high nutrient availability. The present study describes the two establishment strategies for floodplain pioneers based on structural, physiological and reproductive characteristics of the two species, measured in the lower Rio Solimoes/Amazon River, Brazil, and in experiments performed at the INPA (Amazon Research Institute, Manaus). Despite several traits shared by the two species (many small seeds, high germination rates, high CO2-assimilation, fast initial growth, low maximum age, wood with high increments and low density), most physiognomic, structural and reproductive traits indicate two distinct establishment strategies which represent two extremes within a continuum of possible growth habits, and emphasize that also in ecosystems which have adverse growth conditions with prolonged flooding of up to 230 days every year and a water column of more than 10 m, the guild of pioneer trees does not necessarily form a homogeneous group.
