Holocene Savannah Rainforest dynamics of the Northern Amazon.

Overview

Savannahs are important ecosystems accounting for 20% of the global land-surface and account for an equal percentage in global net carbon uptake. However, emphasis on the role of grasslands in terms of carbon storage is often overshadowed by that of forests, which have received much more attention. The Northern Amazon basin is rich in Amazonian savannahs and while these ecosystems are highly biodiverse and offer important ecosystem services to locals, they are also poorly understood and understudied. Interestingly, in contrast to savannah ecosystems elsewhere, Amazonian savannahs are almost entirely devoid of grasses, their place being taken by endemic ancient Guyana-shield (grass-like) monocotyledon taxa which make up the bulk of the vegetation. These savannahs form characteristic mosaics with rainforest occupying large areas of the Rio Negro in the Amazon basin, and typically are found predominantly on nutrient-poor white sand substrates. It is believed that these savannahs depend on fire as a disturbance agent to prevent forest encroachment promoting their diversity. These ecotones appear extremely sensitive to Anthropogenic disturbance. In the absence of palaeoecological records, nothing is known about Anthropogenic effects on vegetation dynamics, equally not much is known about the natural drivers either. The aim of this study is to determine how climate and humans have shaped this landscape.

We present an exciting opportunity, as we have obtained a substantial amount of peat records from the Colombian Amazon. These peatlands are close to the savannah-forest ecotones and are thousands of years old, and provide us with a unique archive that will allow us to study the palaeoecological history of these ecosystems. Because of the complete lack of comparable data, there is no evidence of how fire, humans and climate have affected these ancient Amazonian forest-savannah ecotones. This study will produce the first Holocene environmental reconstruction of the entire region. We anticipate that our peat records will provide important evidence about the evolution of the forest-ecotone dynamics over the Holocene and Anthropocene. We aim to answer the fundamental question: what are the factors that encourage for Savannahs in the Northern Amazon?

Figure 1. Guacamaya superba or Inirida flower. Endemic monocotyledons such as these replace the role of grasses in this white sand Amazonian Savannah.