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Savannahs soon to be covered in trees not grass, researchers say

New research from researchers based at two German research institutes predicts that large parts of Africa's savannahs may well be forests by the time the year 2100 comes round.

Writing in the journal Nature, Steven Higgins from the Goethe University Frankfurt and Simon Scheit...
Savannahs soon to be covered in trees not grass, researchers say
New research from researchers based at two German research institutes predicts that large parts of Africa's savannahs may well be forests by the time the year 2100 comes round.

Writing in the journal Nature, Steven Higgins from the Goethe University Frankfurt and Simon Scheiter from the Biodiversity and Climate Research Centre (BiK-F) in Frankfurt suggest that fertilisation by atmospheric carbon dioxide (CO2) is leading to major increases in tree cover throughout Africa.

Grasses and trees differ fundamentally in their response to temperature, CO2 supply and fire, and continually struggle for dominance in savannahs.

Previously, these shifts in dominance have taken place over long periods of time, but the current wave of atmospheric changes has sped up rates of change.

Once a critical threshold of CO2 concentration is exceeded, savannahs become less grassy and more forest-like. However, each savannah has its own critical threshold which means that each savannah will make the switch at different times. This helps reduce the risk of a simultaneous and dramatic change emanating from the savannahs.

Although most experimental studies have shown that plants do not show a large response to CO2 fertilisation, Steven Higgins explains that most of these studies were conducted in northern ecosystems or on commercially important species.

He explains that so far 'only one experimental study has investigated how savannah plants will respond to changing CO2 concentrations'.

'This study showed that savannah trees were essentially CO2 starved under pre-industrial CO2 concentrations, and that their growth really starts taking off at the CO2 concentrations we are currently experiencing.'

The changes in vegetation predicted by this study can be labelled 'catastrophic regime shifts' and they can be triggered by small changes in the factors that regulate the system. These small changes set up a cascade of events that reinforce each other causing the system to change more and more rapidly. The study demonstrated that the savannah complex showed symptoms of catastrophic regime shifts.

Stephen Higgins comments: 'The potential for regime shifts in a vegetation formation that covers such vast areas is what is making earth system scientists turn their attention to savannahs.'

This study discovered that locations where the temperature rise associated with climate change occurs rapidly, for example in the centre of southern Africa, are projected to switch later to forest as the high rate of temperature increase allows the savannah grasses to remain competitive for longer in the face of rising atmospheric CO2 concentration. This means that even though a single location may experience its catastrophic regime shift, the vegetation change when averaged over a region will be smoother. Such gradual transitions in regional vegetation patterns will reduce the potential for shocks to the Earth's system.

Stephen Higgins emphasises that although such trends may appear to be reassuring, when considered in terms of geological time scales they are in fact very rapid.

Source: Biodiversity and Climate Research Centre (BiK-F)

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Countries

  • Germany
Record Number: 34780 / Last updated on: 2012-06-29
Category: Other
Provider: EC