Increasing dominance of large lianas in Amazonian forests

Ecological orthodoxy suggests that old-growth forests should be close to dynamic equilibrium, but this view has been challenged by recent findings that neotropical forests are accumulating carbon and biomass, possibly in response to the increasing atmospheric concentrations of carbon dioxide. However, it is unclear whether the recent increase in tree biomass has been accompanied by a shift in community composition. Such changes could reduce or enhance the carbon storage potential of old-growth forests in the long term. Here we show that non-fragmented Amazon forests are experiencing a concerted increase in the density, basal area and mean size of woody climbing plants (lianas). Over the last two decades of the twentieth century the dominance of large lianas relative to trees has increased by 1.7–4.6% a year. Lianas enhance tree mortality and suppress tree growth, so their rapid increase implies that the tropical terrestrial carbon sink may shut down sooner than current models suggest. Predictions of future tropical carbon fluxes will need to account for the changing composition and dynamics of supposedly undisturbed forests

Late twentieth-century patterns and trends in Amazon tree turnover

Previous work found that tree turnover, biomass, and large liana densities increased in mature tropical forests in the late 20th century, indicating a concerted shift in forest ecological processes. However, the findings have proved controversial. Here, regional-scale patterns of tree turnover are characterized, using improved datasets available for Amazonia that span the last twenty-five years. The main findings include: trees at least 10 cm in diameter recruit and die twice as fast on the richer soils of western Amazonia compared to trees on the poorer soils of eastern Amazonia; turnover rates have increased throughout Amazonia over the last two decades; mortality and recruitment rates have tended to increase in every region and environmental zone; recruitment rates consistently exceed mortality rates; and increases in recruitment and mortality rates are greatest in western Amazonia. These patterns and trends are not caused by obvious artefacts in the data or the analyses, and cannot be directly driven by a mortality driver such as increased drought because the biomass in these forests has simultaneously increased. Apparently, therefore, widespread environmental changes are stimulating the growth and productivity of Amazon forests. © The Royal Society 2005. All rights reserved