The trouble with trees: what is the benefit of afforestation?
Hailed as a resolution in the fight to reduce greenhouse gases (GHG) and global warming, tree planting programmes have been seen as a major player in conservation. But, new research, published this week, questions the viability and validity of large-scale afforestation. Might we be barking-up the wrong tree to protect Earth’s fragile environment?
While restoration of recently deforested areas has been acknowledged as an important factor in helping to reduce further increases in GHGS, the significance of planting vast areas that have never been forest has not been well scrutinised. An article*, published in Trends in Ecology and Evolution examines the possibility that plans for large-scale tree planting, far from offering hope, distracts from the urgent problem of reducing use of fossil fuels and transforming energy systems.
Against a backdrop of growing scientific skepticism over the contribution of afforestation, William Bond, from the University of Cape Town, Nicola Stevens and Guy Midgley, from Stellenbosch University and Caroline Lehmann of the Royal Botanic Garden Edinburgh have been examining the supposed benefits – and potential losses – of mass tree planting. Their focus: the ambitious AFR100 plan to plant 100 million hectares of trees in Africa by 2030.
The vast area – more than four times the size of Britain – is the subject of a pledge by 28 African countries, signing up to AFR100, to afforest an explicit target area. Mozambique, for example, has committed to ‘restoration’ of one million hectares, South Africa to 3.6 Mha, Kenya to 5.1 Mha, and Cameroon to 12 Mha. Cameroon’s pledge requires converting a quarter of the country to plantations, and Nigeria’s 32 per cent.
But, Bond and colleagues argue the programme will not contribute significantly to GHG reduction, that the funding is a small fraction of that really required to stem CO2 increases, and that African countries are locking themselves into a novel land use for decades without considering the costs to their own future.
With carbon dioxide, the major GHG, increasing at a rate of 4.7 Gigatons per year (1 Gt is one billion tons), the researchers have evaluated the AFR100 programme by considering the cost required to nullify the yearly increase. Their conclusion: “You would need to fork out $47 billion at a very conservative 10$ per ton of carbon sequestered,” explained Bond. “The World Bank’s contribution of a billion dollars is less than 0.5 per cent of what would be needed over the next 10 years. And that billion dollars, spread over 100 million hectares of Africa, works out at $10 per hectare – a bargain for the industrial countries of the world.”
If Africa reached its target of 100 million hectares afforested, the reduction in the annual increase of atmospheric CO2 would be less than 3 per cent per year, they have calculated. “If that seems small, consider that the coal used in the industrial revolution took 400 million years to accumulate,” added Nicola Stevens. "Can you really expect to stuff it all back again in the next few decades?”.
Africa was targeted for the afforestation as the continent’s considerable grasslands and savannas, with climates that can support forests, were wrongly considered to be deforested in colonial times. The researchers have concluded that by converting these grassy landscapes to plantations of eucalypts and pines could condemn citizens in these countries to a century or more of plantation forestry. That means suppressing plantation fires, felling trees and storing the carbon produced, and replanting every decade or two for the foreseeable future. The amount of carbon stored will depend on such intensive management. Furthermore, there is not even scientific agreement on whether plantations will warm or cool the planet. Trees have darker canopies than grassy vegetation absorbing more sunlight and heating the land surface, a problem not yet included in the calculations of afforestation advocates.
In Africa, the vast new forests will be at the expense of food crops, livestock farming and conservation of Africa’s rich diversity of savanna animals and plants. It will also reduce the dry season flow of streams and rivers. “The rush to implement AFR100 has left little time for sober evaluation of the multiple costs and benefits to countries across Africa that have promised large chunks of their land to afforestation. For tree planting to be positive it needs to be the right trees in the right places” said Caroline Lehmann.
As Guy Midgley said “Africa is poised on the brink of rapid urbanization and industrialization. We suggest that environmentally conscious citizens can support renewable energy, energy-efficient buildings, electric cars, solar heating and cooling and other means or reducing GHG emissions. Such actions will rapidly and effectively help reduce greenhouse gases without destroying Africa’s grass-based livelihoods and iconic savanna ecosystems.”
*From Article in Trends in Ecology and Evolution by:
William J. Bond (1), Nicola Stevens (2), Guy F. Midgley (2), Caroline E.R. Lehmann (3), The Trouble with Trees: Afforestation Plans for Africa, Trends in Ecology and Evolution (2019)
(1) Department of Biological Sciences, UCT and Honorary Research Fellow, SAEON
(2) Department of Botany and Zoology, Stellenbosch University
(3) Tropical Diversity, Royal Botanic Garden Edinburgh, Edinburgh EH3 5LR, United Kingdom
University of Cape Town
UCT is the oldest University in South Africa and the leading research university in Africa according to world rankings.
Stellenbosch University is among South Africa's leading tertiary institutions based on research output, student pass rates and rated scientists, and is recognised internationally as an academic institution of excellence. Located in the centre of the historical oak-lined university town amongst the Boland Mountains, it is home to an academic community of 29 000 students (including 4 000 foreign students from 100 countries), spread over five campuses.
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