By Chris Lang
The African Forest Landscape Restoration Initiative (AFR100) aims “to bring 100 million hectares of land in Africa into restoration by 2030”. AFR100 is an offshoot of the Bonn Challenge. The Bonn Challenge aims to “restore forest landscapes” over an area of 350 million hectares by 2030.
But a recent paper in Trends in Ecology & Evolution argues that,
[T]he afforestation envisaged by the global tree planting programmes is based on wrong assumptions. Far from being deforested and degraded, Africa’s savannas and grasslands existed, alongside forests, for millions of years before humans began felling forests.
The paper is titled “The Trouble with Trees: Afforestation Plans for Africa”, and is written by William Bond of the University of Cape Town, Nicola Stevens and Guy Midgley of Stellenbosch University, and Caroline Lehmann of the University of Edinburgh and the University of the Witwatersrand.
The authors are not opposed to trees. They write,
We strongly endorse tree planting to restore closed forests destroyed in historical times (reforestation), the retention of intact forests that remain, and the planting of trees
in urban areas for shade and enjoyment.
But they are opposed to tree planting over vast areas of African savannas.
They note that the areas targetted for “restoration” are based on global maps such as World Resources Institute’s Atlas of Forest Landscape Restoration Opportunities. A 2015 paper in BioScience found that the atlas identifies 900 million hectares of ancient grassy biomes as having potential for tree planting.
The paper points out that this is a “profound misreading of Africa’s grassy biomes”:
The maps erroneously assume that low tree cover, in climates that can support forests, are ‘deforested’ and ‘degraded’. The bizarre result is that ancient savanna landscapes, including the Serengeti and Kruger National Park, are mapped as deforested and degraded (because tree cover is reduced by elephants, antelope, and several million years of grass-fuelled fires).
A brochure on the AFR100 website boasts that 30 countries have committed to restore a total of 126 million hectares. Under the AFR100, Cameroon has pledged to plant trees on 12 million hectares of land. That’s a little more than a quarter of the area of the country.
Aid agencies, including the World Bank and the German government, have committed US$1 billion and the private sector has committed US$481 million.
The company that has committed the most money to AFR100 may come as a surprise to regular readers of REDD-Monitor. EcoPlanet Bamboo has committed by US$175 million by 2020. For more on why EcoPlanet Bamboo is an extremely dubious source of financing, this is probably as good a place as any to start:
Will plantations cool the planet?
The authors point out that,
Committing such vast areas to plantations for the next century should raise many questions. An obvious one for industrial countries that are funding these projects is whether afforestation (planting new trees, rather than restoring areas known, historically, to have been closed forests) will work to cool the climate.
“There is growing scientific scepticism,” they note. They cite three papers to illustrate this scepticism:
• Smith, P. et al. (2016) Biophysical and economic limits to negative CO 2 emissions. Nat. Clim. Chang. 6, 42
Smith et al. argue that all negative emissions technologies are merely a “distraction from the serious business of reducing emissions by reducing fossil fuel use”.
• Baldocchi, D. and Penuelas, J. (2019) The physics and ecology of mining carbon dioxide from the atmosphere by ecosystems. Glob. Chang. Biol. 25, 1191–1197
Baldocchi and Penuelas “evaluated the potential of the Earth’s ecosystems to sequester carbon and concluded that planting trees will not significantly reduce atmospheric CO2”.
• Lewis, S.L. et al. (2019) Regenerate natural forests to store carbon. Nature 568, 25–28
Lewis et al. argue that “restoration of forests is effective, but that plantation forestry is not. They calculated that if 350 Mha were restored natural forests, 42 gigatons of carbon (GtC) would be sequestered by 2100, compared with 1 GtC for the same area afforested with pines and eucalypts. Their analysis implies that converting African savannas to plantations is pointless as a mitigation measure.”
The authors mention last year’s paper titled “The global tree restoration potential” and written by scientists from the Crowther Lab at ETH-Zürich. The paper claimed that global tree restoration is “our most effective climate change solution”.
The authors obviously wrote their “Trouble with Trees” paper before Science published a series of critiques of the Crowther Lab paper. However, they refer to a personal communication from Joseph Veldman who pointed out that the Crowther Lab’s scientists assumed zero soil carbon stocks in sites targeted for tree planting. Veldman was the lead author of one of the critiques of the Crowther Lab paper.
Tree planting is land hungry
The authors calculate that to absorb the current growth in CO2 in the atmosphere, an area of between 1.4 billion and 4.7 billion hectares of plantations would be needed.
Using the lower, optimistic number would mean planting trees on 85% of Russia. Less productive plantations would mean planting trees on about one-third of the world’s land area.
The authors point out that,
If Africa reached the 100 Mha target, GATM [growth rate in atmospheric CO2] would be mitigated by a mere 2.7% per year. If this seems very small reward for afforesting a continent, consider that the coal that drove 200 years of the industrial revolution took 400 million years to accumulate. How can we possibly expect to grow enough trees to stuff all the carbon back in again in just a few decades?
One of the problems with tree planting, especially plantations of eucalyptus and pines, is that they are vulnerable to fires. The problem will get worse as the planet gets hotter.
Most of the carbon stored in grasslands is stored below ground. It remains there even when the grassland burns.
The authors note that,
The global scale of tree planting promoted by AFR100 and similar programmes ignores local concerns over land tenure, competition with agriculture, and conservation, and imposes this single dominant land use for generations to come.
Then there’s the impact on water supply caused by covering savannas with thirsty, fast-growing trees. “Reduction in streamflow from savanna afforestation will have critical impacts on dry season water supply for local communities,” the authors note.
The authors conclude that,
Given the land use change envisaged for tree planting, over enormous areas, sustained for decades, with such poor gains in carbon reduction, we find it difficult to understand why afforestation is so widely supported.
[ . . . ]
Indeed, trees-for-carbon projects can be seen as a distraction from the urgent business of reducing fossil fuel emissions. Planting 100 Mha of trees, far away in Africa, might reduce the urgency of emissions reductions in industrial countries that are the major sources of greenhouse gases.