I welcome the national plan by the Department of Forestry, Fisheries and the Environment (DFFE) to plant 10 million trees (“Call to plant 10 million trees could give Cape Town back its shade”, Bulletin, January 22).
I would like to add several points to counter the negative issues raised by Bond (“Tree planting drive a threat to ecology, livelihoods”, Bulletin, February 3) and Rebelo (“Trees come at a cost”, Bulletin, February 3).
The DFFE proposal came out of the Paris Accord of 2015 and COP 26 held last year at Glasgow. The world has been deforesting at a rate estimated at 10 million hectares per year over the last five years, down from 16 million hectares per year in the 1990s.
The area of primary forest worldwide has decreased by over 80 million hectares since 1990. Each country attending these conferences made a commitment to stop deforestation and to plant millions of trees to offset this loss. South Africa’s commitment to this was 10 million nationally, but not all in Cape Town.
If any trees are to be planted, they should be selected on their suitability for each specific area. Even then, there should be a variety of trees to limit the spread of disease and to enhance biodiversity. Any botanist worth their salt would do this. The first place to start is to see what has been growing successfully locally over the last 50 years. Any layperson will notice that in the urban landscape of Cape Town, there are virtually no indigenous trees, because they are not tall enough and may not survive the pollution and limited water. There are mostly foreign species with a few indigenous South African natives.
There is no evidence that foreign trees use more water than similar sized indigenous trees. Pines and gums are no different and both have adapted to our drought. Under drought conditions gums will reduce their transpiration by closing the stomata in the leaves.
Water use by trees is two-fold - for manufacturing food by photosynthesis and for cooling the “manufacturing sites” on each leaf. Nature has not provided a special photosynthesis process for the Cape’s indigenous fynbos. Don’t let anybody tell you otherwise. Usage of water varies according to the number of leaves on a tree or plant. Hence it stands to reason that the more foliage on the plant/tree the more water it will use for producing sugars. But photosynthesis only operates effectively below a certain temperature and nature has provided trees with a water cooling system. Again, it stands to reason that larger trees will use more water, but this water is not wasted. It cools the environment. This cooling can be as much as 80C – a critical benefit for wildlife and our urban population.
Removing greenhouse gases (GHG) and pollution are important tree functions. Eliminating fossil fuel substantially reduces GHG, but it is not the only source. Domesticated animals produce more GHG than all transport modes combined. Reducing all these animal populations would be very healthy and beneficial.
Soil is not the most effective means for absorbing carbon. If the soil is healthy and porous it can absorb up to 10%. Fynbos soils are too compacted and shallow to absorb much and create high run-off. Peat is more effective and wetlands even more so. Large trees surpass absorption by the soil, because their total leaf surface area far surpasses soil area. However, felling trees, as we have been doing in the Cape, releases all the captured GHG and toxins, which had been safely locked into the matrix over the life of the tree. That is why deforestation dramatically increases all pollutants in the air. Hence, conservation of trees was a prerequisite in the COP 26 directive.
Our limited rain is a precious resource in Cape Town. The objective should be to retain the water on land and reduce run-off to the sea. Roots of trees hold the water and allows a large population of insects, bacteria, and fungi to thrive underground and create a healthy and porous soil for absorbing rain and providing the trees with nutrients whilst reducing erosion.
Our street trees are in a bad situation. They are strangled by concrete and tar, so that rain runs off into the storm-water drains and is lost to the sea. Hence our rain cannot be accessed by urban trees making them entirely dependent on ground water. Trees recycle this water drawing it up to the leaves and is transpired through the stomata into the environment, reducing the ambient temperature and providing moisture for surrounding shrubs, wildlife and mankind. This reduces respiratory problems with lower health costs.
With global warming the focus should be on reducing temperatures. Trees can do this with a limited sacrifice and provide us with health benefits, plus an extra bonus of aesthetics and increased bird population, allowing us to better cope with mental stress. It is in our own interest to make tree-planting possible with our limited rain. We have competent botanists/arborists who can do that.
It is not my intention to debunk the exaggerations made by the academics. Rather, find out for yourself by googling “benefits of trees”. There are many wonderful videos on YouTube. Certainly, sacrificing all the benefits of trees for the sake of fynbos is not in the interests of biodiversity, Capetonians or the heritage of the indigenous people.