Tree Planting as a Natural Climate Solution?  

By Hanna Vogt | Rehabilitating Earth

To avoid the worst effects of climate change, we need to remove greenhouse gases (GHGs) from the atmosphere and stop producing them quickly. Whilst technological solutions like carbon capture technology hold promise, tree planting seems the most obvious solution. The Earth’s forests and soils are currently responsible for removing about 30% of GHGs, and whilst this solution has huge potential, plenty of cases from around the world demonstrate that tree planting can in fact be counterproductive.

Large-scale tree planting projects in Australia and China actually led to biodiversity declining and the worsening of pre-existing local water scarcity issues. This clearly illustrates that tree planting is not the knight in shining armour that the climate needs, as when it is not meticulously planned, the impact on local communities and the natural environment can be devastating. So, what factors do we need to consider to avoid these adverse side-effects?

Replacing Old Trees

For a start, reforestation (planting new trees where previous forests have been cut or burnt down) can never simply compensate for the loss of previous forest lands. Deforestation leads to huge amounts of carbon being released, previously ‘locked-up’ in trees and in the ground. As well as this, it devastates local ecosystems – destroying habitats and subsequently losing the variety of species that lived within them too. 

Planting new forests does not instantaneously make-up for these irreversible impacts. Older trees capture far more carbon than younger ones do, and older forests have more complex and diverse ecosystems. As the biodiversity of the forest plummets, so does the forest’s ability to capture and store carbon. 

The UK’s controversial railway project, HS2, is coming under criticism for exactly this issue. Whilst HS2 claims that the project will be “the most environmentally sustainable railway ever built in the UK”, attempting to salvage ancient woodland soil and replant saplings simply does not compensate for the climatic and environmental impacts of the loss of these woodlands. 

The type of forest and tree can also determine the carbon capture capabilities of woodlands. Tropical forests and boreal forests can store about 240 tonnes of carbon per hectare, whereas temperate forests can ‘only’ store about 155 tonnes of carbon per hectare. Whilst some studies have recently given us some seemingly positive news, reporting an increase of tree cover in some regions of the world, this information has to be put into perspective. Forest area tends to only – if at all – increase in non-tropical areas, whilst deforestation rates remain highest in the world’s tropical regions, such as the Brazilian Amazon. Of course, tree planting efforts in the world’s temperate and boreal regions can still be beneficial for the climate, but they cannot compensate for the unprecedented rates of deforestation in tropical regions (or combat the climate and biodiversity crises) alone. On top of this, trees in recently planted forests are of course also younger – therefore storing less carbon and providing a home for fewer animal and plant species. In other words, to build diverse, ecologically complex systems such as woodlands or rainforests – it takes time. This process is not instantaneous and thus for the full effects of tree planting projects to be reaped, we must be patient. 

What kind of trees, and how trees are planted…

As well as where they are planted, it also matters what kind of trees is planted and how this is done. Tree Planting efforts can only be completely positive if planted trees match the local ecology, landscape, and climate. 

Let’s return to China, a country which has implemented several large-scale afforestation programmes. Afforestation describes the process of planting new forests where previously there haven’t been forests for a long time, or never any at all. Whilst afforestation is technically good in the sense that it is not striving to compensate for deforestation loss and thus could technically be a ‘net benefit’, it can still be harmful. With the goal of stopping desertification, China’s programme has been rolled out in northern arid and semi-arid regions since the 1950s. However, the project has led to several unwanted side effects. Firstly, the planted tree species were not native, and so did not match-up with the local ecology, climate, and landscape. The transpiration (the evaporation of water from leaves) by the planted trees is found to be higher than that of the native tree species. Consequently, the project led to a lowering of the groundwater table, exacerbating pre-existing water scarcity issues which was devastating for local communities. 

Inadvertently the project exacerbated water scarcity issues, a problem which the climate crisis was already making more complex in the arid region. Thus, it is crucial in any tree planting project to diligently consider the local environment and select tree species which are native to avoid any possible adverse effects.   

Moving across the Pacific Ocean to Australia, tree planting is typically carried out in the form of commercial monoculture plantations. Monocultures describe the cultivation of one single plant or tree species (as opposed to cultivating a variety of species). These monocultures often consist of fast-growing species like Radiata pine, a softwood that is endemic to California’s central coast. The introduction and widespread cultivation of the Radiata pine in Australia has led to severe ecological consequences. These include the invasion of native vegetation lands, the alteration of local nutrient cycles, and the decline of biodiversity. Furthermore, monoculture plantations are more susceptible to forest diseases like bark beetle infestations and allow forest fires to spread quicker and further. So, to avoid unwanted and destructive effects such as these, selecting a variety of native tree species and planting them in the form of polycultures is the way to go. A tree planting project carried out in this manner ensures that there is a diversity of species, boosting the carbon capture capabilities of the new forest and protecting local people from adverse side effects such as forest fires. 

Promising approaches within the tree planting sphere

Thankfully, it is not all doom and gloom when it comes to planting trees. There are initiatives which have a wholly positive impact on the climate and local environment. What distinguishes them is that they are designed with the local ecological and human characteristics of the region in mind. 

Community Forests International, for example, emphasise the protection and restoration of forests whilst also pursuing local economic and climate change objectives. They have correctly identified the crucial role forests play in the fight for building climate resilience and climate justice, and they take great care in considering the specificities of the local area. For example, their projects in Zanzibar and Pemba consist of planting and restoring a variety of native tree species (no monocultures here!) that also work for the needs of local communities – boosting food production and income generation

Although tree planting should not be regarded as a climate holy grail since it cannot realistically offset our increasingly rising greenhouse gas emissions, initiatives like Community Forests International’s prove that when diligently planned and carried out tree planting can be a powerful tool in the battle against the climate and biodiversity crises.

Graphic courtesy of Toby Hawksley.