Markedly divergent estimates of Amazon forest carbon density from ground plots and satellites.

Aim: The accurate mapping of forest carbon stocks is essential for understanding the global carbon cycle, for assessing emissions from deforestation, and for rational land-use planning. Remote sensing (RS) is currently the key tool for this purpose, but RS does not estimate vegetation biomass directly, and thus may miss significant spatial variations in forest structure. We test the stated accuracy of pantropical carbon maps using a large independent field dataset.

Are all seeds equal? Spatially explicit comparisons of seed fall and sapling recruitment in a tropical forest.

Understanding demographic transitions may provide the key to explain the high diversity of tropical tree communities. In a faunally intact Amazonian forest, we compared the spatial distribution of saplings of 15 common tree species with patterns of conspecific seed fall, and examined the seed-to-sapling transition in relation to locations of conspecific trees. In all species, the spatial pattern of sapling recruitment bore no resemblance to predicted distributions based on the density of seed fall.

Breeding systems and seed size in a neotropical flora: testing evolutionary hypotheses.

A well-known, but largely untested, prediction in plant reproductive ecology is that dioecious taxa should produce larger, more, higher-quality, or better-defended seeds than cosexual taxa. Using a data set composed of 972 species in 104 families, representing the flora of the Tambopata Wildlife Reserve (Madre de Dios, Peru), we evaluated the first component of this prediction, examining ecological and evolutionary relationships between breeding system and mean seed size with two kinds of tests. First, we conducted cross-species analyses to determine whether species with different breeding systems differed significantly with respect to mean individual seed size.

Effect of distance, aggregation, and habitat on levels of seed predation for two mammal - dispersed neotropical rain forest tree species.

The effect of seed aggregation and distance from conspecific trees on seed predation was experimentally examined for two neotropical tree species, Macoubea guianensis (Apocynaceae) and Pouteria sp. (Sapotaceae) in a lowland tropical rain forest in northeastern Peru. Results of these experiments are discussed in the context of the Janzen-Connell model (Janzen 1970; Connell 1971), which predicts decreased seed survival near parent trees due to either density-or distance-responsive mortality, and Howe's model (Howe 1989) which predicts that trees with seeds dispersed in clumps (aggregated) will not suffer density-dependent predation, and will have higher survival of seeds near the parent tree than other trees.