Holocene histories of biome stability in northern Amazonian savannas

Abstract

Paleoecological analysis of three lake sediment cores from the Roraima savannas in northern Brazil revealed systems dominated by Poaceae pollen throughout most of the Holocene. A slight increase of palms and woody taxa, probably linked to wetter conditions, is observed during the last 1000 years but is more noticeable after 300 and 150 calibrated years BP (yr BP) respectively. Charcoal was present throughout affirming the importance of fire for the landscape but showed the highest values mostly in the last millenium. Poaceae pollen size spectra varied considerably, showing more variability than the overall pollen record. Despite evidence of some climate change in the Holocene, these savannas were stable systems. The sedimentary records showed gaps in deposition between 10,000 and 7800 yr BP and between 2500 and 1200 yr BP, suggesting dry periods during which lakes most likely dried out or became impermanent and highlighting the sensitivity of these lakes to local water table variation. The establishment of the modern climate in the region is evident after 1000 yr BP.