世界各地防止荒漠化

40 percent of the world's land - home to about two billion people - is arid or semi-arid. The Karoo drylands are just one example of where the earth has dried up to such an extent, that it is no longer agriculturally productive.

Professor Timm Hoffman is the Director of the University of Cape Town's Plant Conservation Unit. He says land degradation is a problem world-wide.

"Research which has measured the changes in productivity over the last thirty years from satellites suggests that about 25% of the global surface has lost, or is losing productivity. This is measured in response to cultivation, in response to harvesting, resource-extraction, and as a result also of over-grazing."

According to the United Nations Conference on Desertification, 73% of Africa's drylands are affected by desertification.

South Africa is largely arid or semi-arid, and according to the South African National Biodiversity Institute, about a quarter of the country is severely degraded. This sometimes manifests as eroded gulleys following over-grazing of vegetation.

In the Eastern Cape province, over-grazing by non-indigenous angora goats farmed for mohair, has resulted in a large shrub known locally as spekboom being severely depleted.

Soil fertility and water-holding ability have been lost as a result. Only about 14% of the original healthy spekboom-rich thicket remains, as PhD student Marius van der Vyver explains.

"300 years of goat-browsing - injudicious goat-browsing - by land-owners has degraded most of the spekboom in the area. The area is naturally dominated by spekboom, which is what you see here behind me. And it is a very palatable shrub - goats love the stuff, also indigenous herbivores. But the goats, because of the numbers and the constancy of browsing, they depleted the area."

Van der Vyver's PhD is in the restoration of spekboom-dominated areas, much of which is now degraded land.

The shrub is very valuable in preventing desertification in the dry thicket landscape.

It grows quickly, and prevents erosion by binding the soil.

For these and more reasons, the South African government's Working For Land programme has for the last seven years, been restoring large tracts of degraded land, and already more than 2000 hectares have been replanted with spekboom.

Professor Richard Cowling of the Nelson Mandela Metropolitan University and the Restoration Research Group explains the value of reintroducing spekboom.

"It produces a huge amount of litter - leaf litter. It sheds lots of leaves. So if you put a little canister under spekboom you're going to pick up as many leaves as you would in some of the rainforests. And that enriches the soil enormously, and builds up the organic matter, which enables the soil to hold more moisture, so it's a self-augmenting process of building up an ecosystem that's really healthy. And spekboom can kick start that - it's a kind of an ecosystem engineer."

For a dry area plant, spekboom sequesters, or stores, a high amount of carbon.

The Restoration Research Group is working on accessing further funding for spekboom restoration from the carbon credit market.

Starting with early field trials by farmers, this method of restoration is now being implemented in nature reserves.

For CRI, I am Li Dong.