政二 B 邱科翰 (3) 補交

How shrubs can help solve climate change (節選)

政二 B 07114248 邱科翰

By Alexander Matthews, BBC Future

4th February 2020

In South Africa, there used to be a thicket the size of Cyprus that could sink large quantities of carbon and create a cooler microclimate. These people are trying to grow it back.

“We last had proper rain in 2014,” winemaker Margaux Nel tells me. The two dams on her family’s farm in the semi-arid region of Klein Karoo in South Africa have been dry for the past three years. Less than half of the family’s 60 hectares (148 acres) of vines have survived the prolonged drought, and even less will be able to provide fruit for this year’s harvest.

“We decided we needed to do something,” she says. That “something” has taken the form of planting one million cuttings of Portulacaria afra over the next five years. This succulent shrub, more commonly known as spekboom, has small, round leaves and is indigenous to the area. When these plants have reached maturity in more than a decade’s time, they’ll be up to 5m (16.4ft) high – more than twice the height of a tall adult. They will cast pools of cooling shadow in spite of the dry heat typical of this landscape. The ground surrounding them will be covered with leaf litter – discarded remnants of their tiny bright leaves – as well smaller shrubs that can flourish in their shade.

The reason for Nel’s enthusiasm and that of many growers in the region is that this humble, hardy, semi-desert plant has the potential to alter both the weather, by bringing rain, and the climate, by absorbing carbon dioxide.

Nel’s farm is one small piece of the jigsaw in restoring the thicket. On her vineyard, a team of 10 people plant hundreds of spekboom cuttings every week on the 2,200 hectares (5,536 acres) of land that her father bought for conservation purposes 20 years ago. But to have real impact, the scale of the replanting needs to be orders of magnitude greater. The South African government’s Working for Ecosystems programme proposes restoring a million hectares (2.5 million acres) of spekboom thicket – an area roughly equivalent in size to Cyprus.

Not only would the spekboom suck large amounts of carbon out of the air, but it “would also provide a cooler micro-climate, one that allows other species of animals and plants to return to the area,” Christophersen adds. The cooler temperatures would be a result of the shade cast by the spekboom’s branches, as well as the release of water from the plant’s stomata, a process known as evapotranspiration. Animals that could thrive in the replanted thicket include Big Five wildlife – black rhinos and elephants in particular adore this habitat. It would also be able to support greater numbers of sheep and goats than degraded land currently can, while also encouraging biodiversity in other ways, with the growth of smaller plant species that thrive in the spekboom microclimate.

For more than a decade, the South African government has covered the labour costs for the replanting of an initial 7,400ha (18,285 acres) of spekboom in national parks and on private land. Christo Marais, who oversees the initiative as chief director of Natural Resource Management Programmes at the Department of Environmental Affairs, Forestry and Fishing, estimates that a further 3,000ha (7,413 acres) has been planted through private funding. With a budget of just R120m (£6.3m; $8.2m) annually for ecological restoration, Marais hopes that private landowners, like Nel, and non-profit organisations can step in to take the lead.

Thriving patches of spekboom help to prevent erosion of precious topsoil and silting up dams. Another major benefit to the planting of spekboom on degraded land is the drastic increase in the amount of carbon in the soil that comes both from its roots and leaf litter, as well as the presence of other, smaller plants that are able to grow around it.

The higher carbon content, in turn, improves water retention. Research by Anthony Mills, a soil scientist at Stellenbosch University, has estimated that one hectare of restored spekboom results in 255,000 litres (56,092 gallons) of retained water. Restoring the thicket in full, would result in more than 200 billion litres (44 billion gallons) of additional water being stored in the ground – equivalent to half the capacity of Cape Town’s largest dam.

The reason some of the farmers in Baviaanskloof threw their efforts into spekboom was not just for its ecological benefits, but for financial ones. Farmers hoped to find a source of income from spekboom’s ability to act as a carbon sink,. “When we started planting in 2008, we believed that one day we’d be able to sell carbon credits, which can replace the income from farming animals,” says Zandvlakte’s owner, Piet Kruger.

A drastic fall in the price of carbon credits in the past decade meant those plans had to be put on hold. Nevertheless, Kruger remains hopeful. In spite of four years of drought – which, he says is “abnormal: we haven’t experienced something like this” – the spekboom is growing. He recently observed mycorrhizal fungi growing on the organic matter under the plants. “That means all the soil biology is busy restoring under these plants. It’s a wonderful sign – we can definitely turn degraded land into productive land again, and that gives me hope.”

Spekboom planting is already having other benefits in the area. Government-led planting projects have, according to the South African government’s Marais, provided 1,000 person-years of work (equivalent to 89 full-time jobs a year). And Marijn Zwinkels, the co-director of the Living Lands says this non-governmental organisation is the largest private employer in the Baviaanskloof, with 24 permanent employees involved in planting and other ecological restoration activities, giving a boost in an area with high unemployment

There are other challenges farmers face too. “To make land available for restoration, you need to remove the livestock from those areas. That’s a loss of income for the farmers,” says Kruger. The livestock would only be able to resume grazing once the spekboom matures, which takes over a decade. That might be less of a problem for winemakers like Margaux Nel where livestock is not part of the picture, but for farmers relying on livestock it is a significant commitment.

Nevertheless, Marais – a self-described “realistic optimist” – remains bullish about scaling up spekboom planting. He says that already South African petrochemicals giant Sasol is in talks with his department about ecological restoration to help offset its carbon emissions. South Africa’s carbon tax, which was signed into law last year, could also provide additional sources of revenue to aid planting efforts. And new rules for a reformed carbon market are due to be finalised at the COP26 talks in Glasgow at the end of 2020, which could lead to an invigorated trading system and an increase in the value of carbon credits. This would make setting aside land for spekboom planting much more enticing to farmers.

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心得 : 

  本篇報導聚焦在由南非小 Karoo 地區的居民所發起, 結合 NGO 與政府的力量, 種植樹馬齒莧的計畫。 如果不仔細詳讀, 或許會以為這只是普通的綠化活動, 但它其實有調節氣候, 增加生物多樣性, 對抗土壤退化 (因而提高農業生產力), 增加就業, 與開發新收入來源等多重效用。 很少在地發起的志願活動能有這麼大的影響, 這或許也是為何它能吸引南非政府的補助和科學家的興趣。

  台灣或許能從小 Karoo 的個案學到什麼。 比方說, 在規劃常見的 “社區美化”, “區域綠化” 計畫時, 應能試著效仿小 Karoo 的居民, 做全盤評估, 探索不同可能, 將附加價值與周邊效益最大化。 另外, 台灣許多鄉村雖然還不至於稱得上 “土壤退化”, 但農業生產卻著實下降了, 採取這種模式是否能帶來改變 ? 若想為偏遠村里創造較長期的工作機會, 這種可以活化地方的種植計劃能否促成良性循環 ? 在 “ 新農業” 開始受到關注的今日, 如何擴大 “新農業” 的範圍, 發展更多應用, 並在地紮根, 是值得留意的。