Evidence for arrested succession in a liana-infested Amazonian forest
Résumé
1. Empirical evidence and modelling both suggest that global changes may lead to an increased dominance of lianas and thus to an increased prevalence of liana-infested forest formations in tropical forests. The implications for tropical forest structure and the carbon cycle remain poorly understood.
2. We studied the ecological processes underpinning the structure and dynamics of a liana-infested forest in French Guiana, using a combination of long-term surveys (tree, liana, seedling and litterfall), soil chemical analyses and remote-sensing approaches (LiDAR and Landsat).
3. At stand scale and for adult trees, the liana-infested forest had higher growth, recruitment and mortality rates than the neighbouring high-canopy forest. Both total seedling density and tree seedling recruitment were lower in the liana-infested forest. Stand scale above-ground biomass of the
liana-infested forest was 58% lower than in the high-canopy forest.
4. Above-ground net primary productivity (ANPP) was comparable in the liana-infested and highcanopy forests. However, due to more abundant leaf production, the relative contribution of fast turnover carbon pools to ANPP was larger in the liana-infested forest and the carbon residence time
was half that of the high-canopy forest.
5. Although soils of the liana-infested forest were richer in nutrients, soil elemental ratios suggest that liana-infested forest and high-canopy forest soils both derive from the same geological substrate. The higher nutrient concentration in the liana-infested forest may therefore be the result of a release of nutrients from vegetation after a forest blowdown.
6. Using small-footprint LiDAR campaigns, we show that the overall extent of the liana-infested forest has remained stable from 2007 to 2012 but about 10% of the forest area changed in forest cover type. Landsat optical imagery confirms the liana-infested forest presence in the landscape for
at least 25 years.
7. Synthesis. Because persistently high rates of liana infestation are maintained by the fast dynamics of the liana-infested forest, liana-infested forests here appear to be the result of an arrested tropical forest succession. If the prevalence of such arrested succession forests were to increase in the future, this would have important implications for the carbon sink potential of Amazonian forests.