How Shrubs Can Help Solve Climate Change

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.

By Alexander Matthews

3rd February 2020

"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.

Because of spekboom's remarkable growth rate, its rate of carbon capture can rival that of tropical forests," Sarah-Jane Paviour writes in her 2014 thesis on these properties of spekboom, also called the dwarf jade plant or porkbush. It doesn't need to be cultivated in a nursery before planting, which takes times and money. The result is that one tonne of CO2 can be captured for less than a tenth of the cost of sinking the equivalent carbon by planting trees in temperate or tropical forests. To plant spekboom, all you need to do is to take a cutting from an older plant and place this where you'd like to plant it (sandy soil is best). While it slowly establishes a root system, regular watering is crucial.

Survivor

As well as being a fast and cheap option, another appeal of spekboom is that it something of a botanical chameleon. "The uniqueness of a spekboom is closely linked to its changeable physiology," says Rina Grant-Biggs, an ecologist at Rhodes University. During wet periods, plants are physiologically active in the day, collecting CO2 through tiny pores called stomata in their leaves in a process known as C3 photosynthesis. This is the most efficient way to absorb carbon, and the one used by 85% of the world's plants, including spekboom. Like other plants, spekboom uses the CO2 attained to make sugars to fuel growth and the other essential processes of life.

Spekboom can survive through drought, when many other species would die – Kathleen Smart

But when the rains stop, the plant is able to flip its daily rhythm. During drought, the stomata in its leaves are closed during the daytime. This cuts the water loss during the hottest hours of the day. Instead, the plant opens the stomata in its leaves at night to collect the necessary CO2 when it is cooler, so it loses less water through these pores. This night-time photosynthesis is known as Crassulacean acid metabolism, or CAM photosynthesis.

The result of this flexibility, says Kathleen Smart, also of Rhodes University, is that "spekboom can survive through drought, when many other species would die". There are estimated to be about 16,000 species that carry out CAM photosynthesis, but only a tiny minority – about 25 species, as far as Smart is aware – are able to switch between daytime and night-time photosynthesis for the additional resilience it affords them.

Revival

But, while hardy, spekboom is certainly not invincible. The plant used to be a dominant species in the subtropical thicket biome that, by one estimate, used to cover over a million hectares of South Africa. Over the past 150 years, this has drastically shrunk because of persistent overgrazing by sheep and goats.

A change of this scale would be clearly visible from space. The impact on the climate would be enormous – Tim Christophersen

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.

"If we could regreen the entire area, a change of this scale would be clearly visible from space," says Tim Christophersen, head of UN Environment's Freshwater, Land and Climate Branch, and chair of the Global Partnership on Forest and Landscape Restoration. "The impact on the climate would be enormous."

The maximum recorded rate of carbon sequestration in a spekboom thicket is 15.4 tonnes of CO2 per hectare per year. 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.

Rain-bringer

To date, the goal of one million hectares of spekboom thicket is still a long way off, but there are many reasons that people like Nel are persisting. "The changes and potential benefits from restoring thicket are not only due to carbon [sequestration]," says Smart.

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.

This property of spekboom has the potential not just to improve the quality of the soil and vegetation present, but to alter the local weather. "Soil water retention promotes other plant growth, and both these make water available for evaporation, and potentially, rainfall," says Smart. Indeed, research shows that the presence of plants brings rainfall, thanks to the release of water vapour into the air.

Restoration

But sometimes this isn't enough. Zandvlakte, a farm in the Baviaanskloof area where four million spekboom cuttings have been planted over 1,500ha (3,706 acres), is in the midst of its worst drought in living memory.

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.

It's a wonderful sign – we can definitely turn degraded land into productive land again, and that gives me hope – 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.

Since spekboom planting began in earnest, a number of lessons have been learned, says Marais. While spekboom can grow from cuttings, there are no guarantees that they'll survive if they are simply stuck in just any piece of ground. They should be planted on slopes and not at the bottom of valleys where, when young, they can be easily killed by frost. And while mature spekboom is extremely hardy, "drought is a killer" for young plants that are yet to establish root systems. It is for this reason that Kruger says he has hit pause on further spekboom planting on his farm – he plans on waiting until after more rain arrives before resuming.

Sacrifice

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.

Mills, of Stellenbosch University, agrees with Marais that the goal of one million hectares of spekboom is no mere pipe dream. "Given the current amount of funding available for carbon projects, and because climate change is increasingly recognised as the crisis facing humanity, I do think it's realistic to raise the approximately $1bn (£768m) needed to do this," says Mills. And if this is achieved, he adds, "The win-wins are considerable. Jobs will be created; water supplies will increase; livestock and game carrying capacity will increase."

Countries around the world will be eagerly watching to see if South Africa's experiment is a success. With degraded thicket in dry areas widespread in countries such as Argentina, Chile, Mexico and Madagascar, there is the potential for similar kinds of indigenous plant restoration to replicated elsewhere – again, at a fraction of the cost of restoring forests.

The science behind planting spekboom clearly shows that what is good for the climate is good for biodiversity, and vice versa. However, given that restoring the thicket would boost employment and agricultural productivity, lower temperatures and increased rainfall, it is arguably us humans who stand to benefit most of all. --

Correction This article originally stated that a fully restored thicket could sequester almost three times the emissions produced by the US in 2019, at 5,783 million tonnes. In fact, there was an error in this calculation and the restored thicket could absorb only 15.4 million tonnes per year. We apologise for the error.

Source: https://www.bbc.com