Persistent effects of pre-Columbian plant domestication on Amazonian forest composition.

The extent to which pre-Columbian societies altered Amazonian landscapes is hotly debated. We performed a basin-wide analysis of pre-Columbian impacts on Amazonian forests by overlaying known archaeological sites in Amazonia with the distributions and abundances of 85 woody species domesticated by pre-Columbian peoples. Domesticated species are five times more likely than nondomesticated species to be hyperdominant. Across the basin, the relative abundance and richness of domesticated species increase in forests on and around archaeological sites. In southwestern and eastern Amazonia, distance to archaeological sites strongly influences the relative abundance and richness of domesticated species. Our analyses indicate that modern tree communities in Amazonia are structured to an important extent by a long history of plant domestication by Amazonian peoples.

Complementary N Uptake Strategies between Tree Species in Tropical Rainforest.

Within tree communities, the differential use of soil N mineral resources, a key factor in ecosystem functioning, may reflect functional complementarity, a major mechanism that could explain species coexistence in tropical rainforests. Eperua falcata and Dicorynia guianensis, two abundant species cooccurring in rainforests of French Guiana, were chosen as representative of two functional groups with complementary N uptake strategies (contrasting leaf δ (15)N signatures related to the δ (15)N of their soil N source, NO3 (-) or NH4 (+)). The objectives were to investigate if these strategies occurred under contrasted soil N resources in sites with distinct geological substrates representative of the coastal rainforests. Results showed that species displayed contrasting leaf δ (15)N signatures on both substrates, confirming their complementary N uptake strategy. Consequently, their leaf (15)N can be used to trace the presence of inorganic N-forms in soils (NH4 (+) and NO3 (-)) and thus to indicate the capacity of soils to provide each of these two N sources to the plant community.

Tree diversity in tropical rain forests: a validation of the intermediate disturbance hypothesis.

The "intermediate disturbance hypothesis," which postulates maximum diversity at intermediate regimes of disturbance, has never been clearly proved to apply to species-rich tropical forest tree communities and to local-scale canopy disturbances that modify light environments. This hypothesis was tested on a sample of 17,000 trees in a Guianan forest, 10 years after a silvicultural experiment that added to natural treefall gaps a wide range of disturbance intensities. Species richness, standardized to eliminate density effects, peaked at intermediate disturbance levels, particularly when disturbance intensity was estimated through the percentage of stems of strongly light-dependent species.

Interspecific variability of δ13C among trees in rainforests of French Guiana: functional groups and canopy integration.

The interspecific variability of sunlit leaf carbon isotope composition (δ13C), an indicator of leaf intrinsic water-use efficiency (WUE, CO2 assimilation rate/leaf conductance for water vapour), was investigated in canopy trees of three lowland rainforest stands in French Guiana, differing in floristic composition and in soil drainage characteristics, but subjected to similar climatic conditions. We sampled leaves with a rifle from 406 trees in total, representing 102 species. Eighteen species were common to the three stands. Mean species δ13C varied over a 6.0‰ range within each stand, corresponding to WUE varying over about a threefold range. Species occurring in at least two stands displayed remarkably stable δ13C values, suggesting a close genetic control of species δ13C. Marked differences in species δ13C values were found with respect to: (1) the leaf phenology pattern (average δ13C=-29.7‰ and -31.0‰ in deciduous-leaved and evergreen-leaved species, respectively), and (2) different types of shade tolerance defined by features reflecting the plasticity of growth dynamics with respect to contrasting light conditions. Heliophilic species exhibited more negative δ13C values (average δ13C=-30.5‰) (i.e. lower WUE) than hemitolerant species (-29.3‰). However, tolerant species (-31.4‰) displayed even more negative δ13C values than heliophilic ones. We could not provide a straightforward ecophysiological interpretation of this result. The negative relationship found between species δ13C and midday leaf water potential (Ψwm) suggests that low δ13C is associated with high whole tree leaf specific hydraulic conductance. Canopy carbon isotope discrimination (Δ A ) calculated from the basal area-weighed integral of the species δ13C values was similar in the three stands (average Δ A =23.1‰), despite differences in stand species composition and soil drainage type, reflecting the similar proportions of the three different shade-tolerance types among stands.

The insectivorous-frugivorous diet of the golden-handed tamarin (Saguinus midas midas) in French Guiana.

The diet of Saguinus midas is characterised by analysis of stomach contents samples on an annual and seasonal basis. The diet comprises significant proportions of both fruit and insects all year round, although fruit use shows important seasonal variations. The tamarins reduce their use of fruit resources during the peak fruiting season and instead exploit increased opportunities for insectivory. This is suggested to be a response to differences in gross fruit availability as a function of both fruiting patterns and the presence of competitors for the available fruit resources.