Herbivores help prevent African savannah from becoming a forest

Dec 13, 2013 by Harriet Jarlett
Herbivores help prevent African savannah from becoming a forest
Eland on the savannah

Grazing herbivores play a major role in maintaining savannah landscapes, say scientists.

NERC-funded researchers have been studying a savannah in East Africa over the past ten years to try to understand why trees are so sparse in these grassy areas.

Savannahs are grasslands that are spotted with trees, but these two types of vegetation - grass and trees - require very different light, water and . To co-exist, they create a landscape that's not quite a forest and not quite grassland, and scientists remain in debate about whether or not this coexistence is stable.

Until now, fires were thought to be the main factor in preventing trees from taking over the landscape and turning it into woodland. But this latest research has shown that grazing in the area may be just as important.

'Herbivores play a dual role in maintaining a savannah landscape,' says lead-author Dr Mahesh Sankaran, of the University of Leeds and the National Centre for Biological Sciences (NCBS) in Bangalore, India. 'Smaller herbivores graze on lower seedlings and saplings, preventing them from growing into larger things. While larger bodied herbivores, like elephants, knock down trees , stop them from growing as much and prevent them from dominating.'

By eating saplings before they have a chance to grow, the herbivores prevent the trees from encroaching on the landscape and turning it into a woodland.

The experiment was carried out in a controlled area, where 10 years ago scientists mapped and measured every single tree. In this area fires, which are known to harm sapling trees and maintain a savannah landscape, are suppressed . The scientists were intrigued as to what other factors could be maintaining the balance of grass and trees.

They closed off some areas to exclude animals so that after a decade, when the scientists returned, they could assess which trees had survived and what effect animals had in the areas they could reach.

The team found that without herbivores, seven times more trees grew during the ten year study period . This was the first study ever to track individual trees in an African savannah where herbivores have been excluded.

"Our results demonstrate unequivocally that herbivores have a dramatic influence in maintaining savannahs , and removing them could cause to rapidly take over," Sankaran says.

The work was carried out in close collaboration with researchers from the Rangeland Resources Research Unit, USDA in Colorada, USA.

Explore further: Can pollution help trees fight infection?

More information: Sankaran, M., Augustine, D. J., Ratnam, J. (2013), Native ungulates of diverse body sizes collectively regulate long-term woody plant demography and structure of a semi-arid savanna. Journal of Ecology, 101: 1389-1399. DOI: 10.1111/1365-2745.12147

Related Stories

Airborne technology helps manage elephants

Aug 06, 2012

For years, scientists have debated how big a role elephants play in toppling trees in South African savannas. Tree loss is a natural process, but it is increasing in some regions, with cascading effects on the habitat for ...

Avoiding poisons: A matter of bitter taste

Nov 18, 2013

In most animals, taste has evolved to avoid all things bitter—-a key to survival—- to avoid eating something that could be poisonous via taste receptors, known as Tas2r, that quickly spring into action and elicit the ...

Recommended for you

Can pollution help trees fight infection?

11 hours ago

Trees that can tolerate soil pollution are also better at defending themselves against pests and pathogens. "It looks like the very act of tolerating chemical pollution may give trees an advantage from biological ...

Stink bugs have strong taste for ripe fruit

12 hours ago

The brown marmorated stink bug has a bad reputation. And for good reason: every summer, this pest attacks crops and invades homes, causing both sizable economic losses and a messy, smelly nuisance—especially ...

Iceland whaling season underway despite protest

15 hours ago

Icelandic whaling boats have left port to begin the 2015 whaling season, authorities said on Monday as more than 700,000 people signed a petition calling for an end to the hunt.

Study suggests there are only two tiger subspecies

21 hours ago

(Phys.org)—A team of researchers with affiliations to institutions in Germany, Denmark and the U.K. has concluded after extensive research, that there are really only two subspecies of tigers, as opposed ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.