Tree-planting drive a threat to ecology, livelihoods

William Bond, emeritus professor of biological sciences, UCT

I refer to the article (“Call to plant 10 million trees could give Cape Town back its shade,” Bulletin January 20). For over 25 years, the Western Cape has been running a world-class environmental programme removing trees. Surely that calls for some comment on why a government department, decades on, wants to establish millions of the same plantation trees that we have been removing.

The tree-clearing programme stems from a century-old debate on whether plantations of trees increased rainfall or dried up rivers. After many decades of research and monitoring we have a clear answer: trees dry up our rivers. To avoid future Day Zeroes, cutting down alien, invasive trees is a key strategy for sustaining our water sources.

The new call by the Department of Forestry, Fisheries and Environment (DFFE) to plant 10 million trees is part of a global and Africa-wide programme intended to soak up excess carbon dioxide in the atmosphere.

Anyone can see that trees lock up carbon in the tree trunk. What you can’t see is the carbon below ground, which can greatly exceed carbon above ground, in Arctic peatlands, for example.

With the support of oil and forestry companies, politicians (including former American president Donald Trump), and the World Bank, the gobal tree-planting programme has received massive support.

The science behind it is surprisingly thin and is being increasingly questioned by scientists. The trillion trees programme for example was promoted by a paper in Science (Bastin et al. 2019), but subsequent rebuttals showed that the carbon estimates were greatly exaggerated (they ignored soil carbon for example).

Plantations are an uncertain and very slow way of decarbonising the atmosphere. They are not only an inefficient mechanism compared, say, to reduction of fossil-fuel emissions, but tree planting also directly threatens livelihoods of millions of people and thousands of sun-loving plant and animal species. The problem of plantations lowering water tables, very well understood in South Africa, has hardly entered public debate and tree-planting promotions.

It might help to visualise what 10 million trees means. Like all the other big numbers, it bamboozles people to talk about a million, a billion, a trillion. Even the largest trees start off as very small seedlings. So is the target 10 million seedlings? Or stately giants? How big will these 10 million trees be?

The answer really matters for how much carbon they sequester and the area needed to do so. If we choose tall trees and count how many trees you get in one hectare it’s not hard to work out. Two hundred trees per hectare would give you some stately looking tall trees.

Ten million of those would require 500km². That is an area exceeding the entire Cape Peninsula (470km²) including all its urban settlements. So when the enthusiasts for tree planting welcome the 10-million-trees programme do they envisage the whole of the Cape Peninsula covered under trees? Does “giving back Cape Town’s shade” mean swallowing up our famous sun-loving fynbos under pine trees?

This is not giving Cape Town back its shade – it’s creating shade that was never there before. Planting those 10 million trees would destroy all the biological uniqueness of the Cape Peninsula.

It makes sense to plant trees in cities and their gardens, for shade and recreation. But does it really make sense to cover remaining natural areas with even more plantations than those that already exist?

How should we deal with the flood of calls for tree planting to save the planet? What should we be doing to reduce climate change risks? Why plant a tree? Why not a solar panel or better roof insulation?

I like trees and have planted quite a few. If you really want to plant trees, it is helpful to ask: is this the right tree, in the right place and for the right reasons?

Avoid fast-growing alien invasives. Short-term gain will leave a centuries-long headache. Avoid planting in pristine, native vegetation. What are you destroying? Beware planting trees to decarbonise the world. You may lose more carbon from disturbing virgin soils, or if the stored carbon goes up in smoke in a plantation fire.

Beware the European forest fetish. Celebrate the magnificent views in South Africa, which plantations would obscure. Insist that Europe, and South Africa, fight climate change by the quickest and most effective means: reducing fossil-fuel emissions.