Published at 2020, January 31th
Can planting trees can help stop climate change and mitigate its consequences? As trees have a great potential for carbon sequestration and they are often seen as a great natural technology against global warming – but is this always true? Let’s jump into the secret world of trees to better understand their capabilities.
Trees And Climate Change: Carbon Absorption Potential
As trees grow, they help absorb and sink the carbon that would otherwise contribute to global heating. Trees (together with all plants) use sunlight energy to do photosynthesis – a process that uses carbon dioxide and water to create energy (glucose) for their cells. In the end, trees end up feeding themselves with the carbon we desperately need to avoid getting to the atmosphere.
In addition to the carbon dioxide trees capture, they also help the soil capture and store carbon. Despite not doing such an incredible job as oceans do – absorbing around 90% of all carbon emissions and then suffering the impacts of ocean acidification – trees are extremely important to help stop climate change.
That’s why the more trees are out there, the better. Unfortunately, as areas of forest the size of a football pitch are being lost every minute, we’re yet to get to the right track when it comes to forest protection and management. But this piece ain’t about what’s going wrong with forests. This is about why it is so important that things go right.
Planting Trees Can Help Stop Climate Change. But How Many Trees?
The global tree restoration potential study published in the journal Science had several scientists analyzing the global tree cover situation. They used 80,000 high-resolution satellite images from Google Earth to measure tree cover and then mixed these results with soil, topography and other climate variables using AI. The result was a global map of where more trees could be planted to help stop climate change.
The results from the study led by Prof Tom Crowther found that nearly two-thirds of all land – 8.7bn ha – can grow trees and support a forestal area. Of all this space, 5.5bn ha already have trees and another 1.5bn ha corresponds to cropland used for growing food.
Doing the math, it means there is an extra 1.7bn ha with grasslands, degraded soils or lightly vegetated area where more trees can be planted. This area represents around 11% of all land and has the size of China and the US combined. The researchers involved in the study expressly dismissed from the analysis all the land currently being used to grow crops, as well as urban areas. However, they considered grazing land which, they say, can benefit from having trees – a forest management technique known as agroforestry.
This huge area represents the great potential that planting trees can have in helping to stop climate change. In fact, Prof Crowther said he was amazed by the results and by the potential that planting trees can have to fight global warming. This (at the time) unmeasured potential that had previously been suggested by the IPCC, the entity that spoke of the need to increase forest area by 1 billion ha to limit global warming to 1.5ºC by 2050 – was one of the goals of the study. One that ends up being very valuable as it created a blueprint that clarifies how much tree cover there is and how much more can be planted.
The Urgency Of Planting Trees Globally And How Climate Change Is Faster Than Growing Trees
According to the same study, there is room for growing more 0.9 billion ha of canopy cover that would store 205 gigatonnes of carbon. And citing the authors’ words, we can see global tree restoration as our most effective climate change solutions to date. All these restored forests and woodlands could store 205 Gt of carbon if they were allowed to develop to a similar state of existing ecosystems in protected areas.
This solution is one that needs to find a global consensus and take place a bit everywhere – but especially in 6 main regions. In fact, more than 50% of the tree restoration potential sites can be found in 6 countries: (in million hectares) Russia, +151; United States, +103; Canada, +78.4; Australia, +58; Brazil, +49.7; and China,+40.2.
However, despite the existing potential, according to Prof. Crowther, it would take between 50 to 100 years for all these (expected to be) planted trees to be able to remove 200bn tonnes of carbon. That’s why it is crucial to reduce emissions (currently around 40 GtC per year) while restoring forest areas. But it looks like planting may not always be the best solution.
(One Of The Solutions) To Stop Climate Change Is Planting More Trees. But Not All Is Good
A study led by scientists from Stanford University and the University of Barcelona also highlights the ability of trees to continue to sink carbon dioxide from the atmosphere. Despite warning that as CO2 concentration rise, close attention needs to be given to the soil’s balance of nitrogen and phosphorus concentration, the study also points towards the idea that trees have a great potential to help stop climate change.
Again according to the global tree restoration potential study, if we act now, this could cut carbon dioxide in the atmosphere by up to 25 percent, to levels last seen almost a century ago. Planting trees is cheap (at least compared to high tech sucking carbon technology whose efficiency isn’t proven yet), it’s available and it’s something citizens can easily get involved with.
By betting on planting trees while adapting the existing monoculture plantation forests can become more inclusive and ecological. This will help enrich wildlife and biodiversity while reducing water pollution, soil degradation, and plagues. Nonetheless, there are other studies that question the efficiency of trees and bring up some concerns about the true efficiency in cap and trade systems.
Is Planting Trees The Best Way Of Fighting Climate Change? It Is Not So Straight Forward
A study from the University of California, Davis, discovered grasslands and rangelands are better and more resilient carbon sinkers than forest trees in California. This happens because grasslands “are less impacted by droughts and wildfires” as they “sequester most of their carbon unground, while forest trees stored it mostly in woody biomass and leaves.”
As a result, when they burn, trees release carbon back to the atmosphere, while the carbon fixed by grasslands (which also absorb a lot of carbon) tends to stay in the roots and soils. This suggests grasslands are less vulnerable to (the increasingly likely to happen) weather events, droughts and fires and, therefore, more adaptive to climate change then trees. This means conserving grasslands and promoting rangeland practices that contribute to carbon absorption is very important to meet the reduction targets of GHG emissions.
Moreover, other studies show forests lead to a higher albedo effect (the number of sun rays directly reflected back to space without heating the ground) compared to arable land. It is, therefore, crucial to accurately calculate (depending on the location or the type of land among other variables) the net effect of decreased albedo and carbon storage to figure out whether planting trees truly is the best use for soils. If we consider nutrient-rich and balanced soils have a great carbon absorption potential, deciding whether to prioritize enriching these soils or planting trees can become a hard choice.
Other Issues Rise When Looking More In-Depth To The Potential Of Planting Trees
Indeed, more questions need to be asked before saying out loud and with clear confidence that planting trees all over is, without a shadow of a doubt, the best strategy to fight climate change. How long will planting trees take before changing the levels of co2 in the atmosphere? Can savannas and grasslands support huge increases in tree cover or will it affect the resilience of ecosystems and perhaps even their ability to function as effectively regarding carbon sequestration? How to conciliate the need to plant more trees with the increasingly higher demand for food production?
It is important to consider these questions before speaking about planting trees on a large scale as a good strategy to tackle climate change and reduce GHG concentrations. For instance, one should consider that trees sink carbon as they grow and not right after being planted. Planting single types of species is also dangerous for the natural balance and damaging for the health of soils.
Saatchi, a senior scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, goes even further as to say that we need to consider the phenomenon of climate connectivity. He warns that when ecosystems become too fragmented, they start losing their natural functions which makes it harder for a “reforested area to have its species range and diversity, and the same efficiency to absorb atmospheric carbon.”
In the end, more studies with better satellite observations and modeling (that takes climate connectivity and the current resilience of certain ecosystems into consideration) are needed – Saatchi suggests. They will allow a better understanding of which – if any, as enriching grasslands and arable soils can turn out to be better solutions – regions global forest reforestation efforts should be put. Meanwhile, reducing emissions and restore original forest covers are crucial climate change mitigation strategies.
Photo by Aditya Vyas on Unsplash