HAILED as a resolution in the urgent fight to reduce greenhouse gases (GHG) and global warming, mass tree planting programmes have been seen as a major player.

Yet, while there is certainly much to be said for considered plantings of the right species in appropriate locations for restoration of previously degraded forests, new research questions the viability and validity of large-scale afforestation.

Might we be barking up the wrong tree to protect Earth’s fragile environment?

Restoration of recently deforested areas is acknowledged as important for conservation and in helping to reduce further increases in GHG. However, the significance of planting vast areas that have never been forest has not been well scrutinised. A target for mass tree planting has been the African continent, 50% of which is covered by vast grasslands and savannas with climates that can support forests.

Often wrongly considered to be deforested in colonial times, these savannas and grasslands are regions with unique flora and fauna requiring sun-lit environments.

READ MORE: Stuart Cosgrove: Greta Thunberg's opponents are measure of her success

Mass tree planting will push out a unique biodiversity, as evidenced from studies in Brazil and South Africa, where increases in savanna tree cover led to declines in overall diversity.

Closer analysis indicates that mass tree planting targeting grassland and savanna areas could distract from the urgent problem of reducing use of fossil fuels and transforming energy systems, while having a negative effect on biodiversity.

Against a backdrop of growing scientific scepticism over the contribution of afforestation, studies into the ambitious AFR100 plan to plant 100 million hectares of trees in Africa by 2030 suggest it might not be the best hope for regeneration.

Twenty-eight African countries have pledged to afforest an explicit target area more than four times the size of Britain.

Mozambique, for example, has committed to “restoration” of one million hectares (Mha), 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%. It has received World Bank backing to the tune of one billion dollars.

But it is questionable if the programme will contribute significantly to GHG reduction. Not only is it unlikely the project can stem CO2 increases, but the initiative could lead to African countries locking themselves into a novel land use for decades without considering the costs to their own future in terms of biodiversity, land use and ecosystem resilience in a changing climate.

With carbon dioxide, the major GHG, increasing at a rate of 4.7 Gigatons per year (1 Gt is one billion tons), the cost required to nullify the yearly increase could be as much as $47bn at a very conservative $10 per ton of carbon sequestered. The World Bank’s contribution of a billion dollars to the continental African project, therefore, is less than 0.5% of what would be needed over the next 10 years.

That billion dollars, spread over 100 million hectares of Africa, works out at $10 per hectare.

If Africa reached its target of 100 million hectares afforested, the reduction in annual increase of atmospheric CO2 would be less than 3% per year. If that seems small, the coal used in the industrial revolution took 400 million years to accumulate. It would be unreasonable to expect that situation to be resolved in only a few decades.

To convert grassy landscapes to plantations of eucalypts, pines or even native species could condemn citizens to a century or more of plantation forestry. That means suppressing plantation fires, which can be a threat to life and difficult to control, 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 but also potentially exclude people from using land in other ways needed for sustainable livelihoods.

Yet, there is not even any scientific agreement on whether extensive areas of new forests 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 its rich diversity of savanna animals and plants. It will also reduce the dry season flow of streams and rivers that people otherwise utilise.

The rush to advocate and implement mass tree planting has left little time for sober evaluation of the multiple costs and benefits to countries promising large chunks of their land to afforestation.

For tree planting to be positive it needs to be the right trees in the right places. There is an urgent need to balance local land use needs and biodiversity conservation with a global policy agenda for reducing GHG.

With Africa on the brink of rapid urbanisation and industrialisation, there are other ways to positively impact our environment.

Support renewable energy, energy-efficient buildings, electric cars, solar heating and cooling and other means of reducing GHG emissions.

Such actions at a collective scale combined with advocacy to change our energy systems will be most effective to help reduce greenhouse gases without compromising iconic ancient ecosystems.

These considerations are transferable around the world.

It is important to recognise and respect the diversity of ecosystems and develop GHG mitigation actions that lead to sustainable changes in our energy systems.

We can assess more closely how we improve our understanding and value of grasslands and savannas and their contribution to biodiversity and climate. By being responsible global citizens we can take steps to conserve and restore biomes while combatting climate change.

So much remains to be learned about global organisation, assembly and distribution of plant and animal communities. This is best done when their vegetation, that basis for animal habitats, be it grassland, savanna, forest, desert or tundra or any other habitat, can be assisted in retaining its natural integrity.

Dr Caroline Lehmann is a tropical diversity biologist at the Royal Botanic Garden Edinburgh