Silvermine, Western Cape. Photo Jay Cowen/1999 and John Watermeyer/June 2016. Click on the triangles to slide the picture to one side or the other.

Forests around the world are disappearing. Since 2000, roughly 20% of Africa’s forests have been wiped out. But, according to research by Zander Venter, a UCT agroecology PHD student, trees and shrub appear to be fighting back – at the cost of African savannah. 

Venter analyzed satellite imagery from as far back as 1986 and compared them with South African grasslands today.

“Many of these species are gradually encroaching into grasslands and savannas across Africa, particularly in places like Cameroon and the Central African Republic,” wrote Venter in an article in the Conversation.

Zander Venter. Photo supplied.

"We found that woody plants’ cover has increased in large swathes of the continent in the past three decades," said Venter.

Woody plants provide fuel for rural communities and increased food for browsing livestock like goats. They could also offset the loss in carbon sequestration caused by deforestation.

But woody plants encroaching on grasslands also means less food for cattle and some types of wild herbivore.

It’s difficult to explain the gradual increase in woody cover, but researchers believe the answer may lie in rising levels of atmospheric carbon dioxide (CO2). Some experiments have shown that trees grow faster from elevated CO2 than grasses do.

“In our study we found that fire and herbivores are possibly as important as climate or CO2 emissions in shaping Africa’s savannas. Over the past few decades, as human populations have grown, we have reduced the spread and intensity of fires and replaced browsing animals like elephants, kudu and goats with grazers like cattle. This has allowed woody plants to proliferate," said Venter. 

Satellite observation from content sites like Google Earth Engine and Planet, have given scientists the ability to monitor every point on the planet, every day. 

The pictures, taken by citizen scientists for the repeat photography project rePhotoSA, reveals how woody plants are transforming grasslands. 

By looking at historical photographs, scientists can investigate changes in vegetation over decades and even centuries.

Click on the triangles to slide the picture to one side or the other.


1. Barberton, Mpumalanga.

Pine plantations have expanded since 1946 and bush encroachment has increased. 

Photos: John Acocks/1946 and Nico and Delia Oosthuizen/2015. 


2. Hogsback, Eastern Cape

Note the increase in pine trees across this landscape. 

Photos:  John Acocks/1942 and Justin du Toit/May 2016. 


3. Kei River, Eastern Cape 

A general increase in woody vegetation with a slight increase in development.  

Photos: IB Pole Evans/1923 and James Puttick/August 2010. 


4. Three Sisters, Eastern Cape

The buildings are no longer there, and there has been a general increase in trees and shrubs in the area. 

Photo by John Acocks/1948 and Justin du Toit/April 2016. 


5. Drakensberg, KwaZulu-Natal

 

Photos: Keith Cooper/1992 and Wayne McNamara/April 2016


6. Elsenburg, Western Cape 

Photos: IB Pole Evans/1921 and Samantha Venter/July 2016


7. Kalk Bay, Western Cape

There are many more houses now, particularly in the distance. 

Photos:  IB Pole Evans/1900 and John Watermeyer/August 2016. 

To explore other changes in woody plant coverage, visit this interactive map.


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