Andreas Späth

Africa’s shrinking savannahs

2012-12-18 12:55

Andreas Späth

We’re all conscious of the fate of the world’s tropical rainforests, especially those of the Amazon region. We regularly hear stories of their continuing decimation by human activities like deforestation and slash-and-burn cultivation techniques.

But what about the status of major ecosystems in our own backyard? What about, for instance, our own continent’s iconic grassland savannahs, a type of landscape that’s very close to the heart and soul of many South African’s?

Plight of the lion

A new study published in the journal Biodiversity and Conservation earlier this month sheds some light on the issue from a somewhat unusual perspective – that of free-roaming African lions (Panthera leo) and the results are not particularly encouraging.

Using high-resolution satellite imagery in conjunction with data for the distribution of lion and human populations, the researchers defined the term savannah very broadly as regions south of the Sahara that receive between 300 and 1500 mm of rain per year, excluding montane and tropical forests as well as dry areas such as the Namib.

In 1960, Africa is estimated to have been home to nearly 100 000 lions roaming some 11.9 million km2 of savannah with a human population density of less than 25 people per square kilometre, a figure which is considered to be the threshold above which lions become extinct in an area. Under increasing pressure from factors such as urbanisation and land-use changes through agriculture and forest plantations, this habitat has been shrinking and as a result lion numbers have been declining precipitously.

In 2000 only 9.7 million km2 of savannah inhabited by fewer than 25 humans per km2 remained, and today the total potential range of the continent’s remaining 32 000 to 35 000 lions is estimated at a mere 3.39 million km2 at best.

Trend to continue

This trend is expected to continue as Sub-Saharan Africa’s human population increases - it almost quadrupled from 229 million in 1960 to 863 million in 2010 and is forecast to more than double again to 1.753 billion by 2050.

Twenty seven African countries have resident free-ranging lion populations, but only in nine do numbers exceed 1000. In Central and West Africa, lions are especially threatened, even in National Parks and conservation areas.

But...

On a somewhat more positive note, the study does identify ten regional lion strongholds with stable or growing populations of 500 or more individuals in protected areas. The Southern African strongholds include:

- Kgalagadi (Botswana and South Africa) with about 800 lions;

- Okavango-Hwange (Botswana and Zimbabwe) with about 2300 lions; and

- Great Limpopo (Mozambique, South Africa and Zimbabwe) with over 2100 lions, nearly 1700 of which live in the Kruger National Park.

The greater significance of the study’s focus on lions is, of course, that as the continent’s top predator, their presence in an area represents a good measure of a reasonably intact ecosystem. Ultimately it confirms the very significant impact we humans are having on our natural environment, turning forests into savannah and then savannah into miellie fields and parking lots – a process that was set in motion a long time ago.

In February, a group of French researchers suggested, for example, that human activities (along with regional changes in climate) had a significant role in converting large parts of central African rainforest into savannah 3000 years ago as Bantu-speaking farmers moved into the area from near the present-day border between Nigeria and Cameroon. In the Amazon, studies have shown that burning and deforestation are leading to a similar modern-day process of “savannization”.

In the context of climate change and global warming, we should be worried about more than just the aesthetic implications of losing some of our continent’s most beautiful landscapes though. While forests represent the most important terrestrial carbon sinks, research indicates that savannahs and grasslands play a significant role in sequestering CO2 from the atmosphere by trapping it both in vegetation and soil.

Like the lions, we can’t afford to lose them.


- Andreas freelance writer with a PhD in geochemistry. Follow him on Twitter: @Andreas_Spath

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