Responses of Amazonian ecosystems to climatic and atmospheric carbon dioxide changes since the last glacial maximum

Abstract

The aims of this paper are to review previously published palaeovegetation and independent palaeoclimatic datasets together with new results we present from dynamic vegetation model simulations and modern pollen rain studies to: (i) determine the responses of Amazonian ecosystems to changes in temperature, precipitation and atmospheric CO2 concentrations that occurred since the last glacial maximum (LGM), ca. 21 000 years ago; and (ii) use this long-term perspective to predict the likely vegetation responses to future climate change. Amazonia remained predominantly forested at the LGM, although the combination of reduced temperatures, precipitation and atmospheric CO2 concentrations resulted in forests structurally and floristically quite different from those of today. Cold-adapted Andean taxa mixed with rainforest taxa in central areas, while dry forest species and lianas probably became important in the more seasonal southern Amazon forests and savannahs expanded at forest-savannah ecotones. Net primary productivity (NPP) and canopy density were significantly lower than today. Evergreen rainforest distribution and NPP increased during the glacial-Holocene transition owing to ameliorating climatic and CO2 conditions. However, reduced precipitation in the Early-Mid-Holocene (ca. 8000-3600 years ago) caused widespread, frequent fires in seasonal southern Amazonia, causing increased abundance of drought-tolerant dry forest taxa and savannahs in ecotonal areas. Rainforests expanded once more in the Late Holocene owing to increased precipitation caused by greater austral summer insolation, although some of this forest expansion (e.g. in parts of the Bolivian Beni) is clearly caused by palaeo Indian landscape modification. The plant communities that existed during the Early-Mid-Holocene may provide insights into the kinds of vegetation response expected from similar increases in temperature and aridity predicted for the twenty-first century. We infer that ecotonal areas near the margins of the Amazon Basin are liable to be most sensitive to future environmental change and should therefore be targeted with conservation strategies that allow 'natural' species movements and plant community re-assortments to occur.

Oxygen isotopes in tree rings are a good proxy for Amazon precipitation and El Niño-Southern Oscillation variability

“…18-21 ka ago) indicate that the Amazon was wetter during the LGM than it is today. This finding would be consistent with independent inferences of wetter conditions during the LGM based on lake records in the Altiplano (35), but inconsistent with pollen evidence (36) or Amazon river outflow reconstructions based on a marine foraminifera δ 18 O record (37), indicating that the Amazon was drier than today. A scenario of a drier Amazon seems difficult to reconcile with wetter Andes indicated by ice core records during the LGM.…”

Mitochondrial DNA Detects a Complex Evolutionary History with Pleistocene Epoch Divergence for the Neotropical Malaria Vector Anopheles nuneztovari Sensu Lato

“…The mismatch distribution depicted populations at non-equilibrium for all groups, although the sum of squared deviations goodness of fit test did not reject the null hypothesis, except for subclade II-B. The departure from equilibrium, the star-like network, 70 likely contributed to speciation in this complex. These findings may help to clarify the involvement of An.…”

Trans-Amazon dispersal potential for Crotalus durissus during Pleistocene climate events

“…Although projections from niche modeling algorithms presently provide only a single, generalized snapshot of climatic suitability for a given time slice, they illuminate processes affecting the broader distributional potential of C. durissus since the LIG. A variety of studies, including genetic (Wü ster et al 2005a,b, QuijadaMascareñ as et al 2007, paleoecological (Prado and Gibbs 1993, Pennington et al 2000, Mayle et al 2004 Though still not completely clear, overall understanding of late Pleistocene climatic events and biotic responses in the Amazon Basin has improved significantly in recent years. The vast majority of data feeding this understanding of South America's climate during the Pleistocene derive from sites along the Atlantic seaboard and in the central Andes (Wang et al 2004, Whitney et al 2011; however, limited data also now exist for South America's continental interior (Whitney et al 2011).…”