Tree planting and reforestation projects have taken the world by storm in the past couple of years. The premise seems simple enough. Trees are natural carbon sequesters: they take carbon dioxide out of the air during photosynthesis and turn it into biomass. In reality, tree-planting projects are much more complicated and some even do more harm than good. In theory, reforestation projects are essential if we are to keep global warming below 1.5C, but we need to completely rethink the way we approach reforestation if we have any hope of succeeding.
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The problem with most reforestation projects is best exemplified when looking at global pledges like the Bonn Challenge. Started in 2011 and hosted by the German Government, the initiative called for massive reforestation programmes to be implemented by countries, companies, and individuals. The Bonn Challenge aims to reforest an area of Earth roughly the size of India and says that doing so will sequester enough carbon to keep global temperatures below 1.5C by 2100.
A report by the journal Nature published in 2019 found that out of all the Bonn Challenge pledges, “45% of all commitments involve planting vast monocultures of trees as profitable enterprises.” 21% of pledges involved commitments to agroforestry, which has never been implemented at large or industrial scales. And nearly two-thirds of Bonn Challenge pledges were for agricultural projects disguised as tree planting schemes. Other groups like Nature Conservancy have been criticised for selling carbon credits for fake or overstated tree planting projects, as revealed in a bombshell report by Mark Kauzlarich for Bloomberg. Tree planting projects are not internationally regulated or vetted, so it is far too easy for harmful or untrue practices and claims to be branded as climate solutions.
At the same time, it is far too easy for companies like Shell and BP to buy carbon credits via reforestation projects instead of reducing emissions. At its core, reforestation as a way to offset carbon just isn’t working. In some ways, it is a cop-out. Companies unwilling to decrease their emissions can buy carbon credits and continue to emit without changing their practices, but that doesn’t mean we should stop reforestation. Instead, we need to examine the difference between commercial tree-planting schemes and ecosystem restoration.
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Ecosystem Restoration As A Land Management Strategy
Ecosystem restoration is fundamentally different from mainstream tree planting and reforestation projects because it recognises the nature’s ability to heal itself. In most tree planting schemes, trees germinate, grow off-site, and are hand-planted in the target area. In assisted natural regeneration, sites can regrow with minimal human intervention.
An assisted natural regeneration plan at the Knepp Castle Estate in West Sussex, England, restored a 1,400-hectare forest dotted with flood-prone meadowlands. Workers at the Knepp Castle simply allowed local birds and animals to bring in tree seeds. Brambles and thorny plants grew over target areas, which provided the saplings protection from grazing animals. 20 years later, a thriving ecosystem has completely recovered. The only human interventions involved reengineering the way water flowed through the estate and weeding out invasive species of plants. The forest at Knepp Castle is now home to a biodiverse ecosystem, with more than five species of trees, and hundreds of species of animals.
The biodiversity crisis has had rippling effects in the past couple of years and is intrinsically connected to the climate crisis as a whole. Animals have critical roles to play in the ecosystems they are adapted to. For example, when Yellowstone National Park in Wyoming reintroduced Timber Wolves, they found that the forest floor became more lush, and that rivers running through the park were eroding their banks at a less rapid rate. The wolves’ presence changed the behavior of omnivores like deer, so they didn’t overgraze patches of forest floor and instead chose to move more often, which allowed groundcover to be more lush. Deer also spent less time eating around riverbanks, which allowed plants to stabilize themselves better. Overall, the Timber Wolves made the forest in Yellowstone healthier and better at absorbing carbon.
Restoring ecosystems as a whole makes their overall ability to sequester carbon better. That is not to say that our goal when it comes to reforestation and ecosystem restoration should just be carbon sequestration. Instead, we should prioritise the health of the ecosystems that we restore so that they can harbour biodiversity and cope with severe events like droughts and floods. Some active reforestation projects have burned to the ground as a result of forest fires, rendering their efforts to sequester carbon useless. When trees burn, they release the carbon stored in their trunks back into the atmosphere.
All living things hold carbon in their bodies, and ecosystems sequester carbon in different ways, but all rely on the same underlying principle. When an organism dies, the carbon in its body is re-released into the atmosphere as it decomposes, this includes trees, which rerelease carbon after they die, but that process can take hundreds to thousands of years because trees take a long time to decompose. Some carbon that has been sequestered by forests is stored permanently in soil, but forests need to mature and age for their carbon sequestration to become meaningful in terms of climate change.
We also need to look beyond forest restoration, not only because humans have damaged every type of ecosystem, and as a result, wildlife populations have fallen by 70% in the last 50 years, but because other ecosystems are even better at sequestering carbon.
Among different types of forests, tropical forests sequester the most carbon, but tundra, seagrass meadowlands, kelp forests, wetlands, and mangrove forests are just as good, or even better at sequestration. We analysed the characteristics of each of these ecosystems.
1. Preserving and Restoring Tundra and Permafrost
Tundra stores the most carbon per hectare of any ecosystem. It is found at the poles and in alpine zones and is generally treeless. Tundra is full of grasslands and wildflowers in the summer. Tundra can also be characterised by its permafrost, which is what makes it so good at storing carbon. Permafrost is permanently frozen soil. When plants die as the seasons change in the tundra, they don’t decompose and release the carbon stored in their bodies back into the atmosphere because they are frozen and become permafrost. Permafrost can become incredibly thick and is up to 1,000 metres deep in some places. At the same time, some permafrost can be hundreds of thousands of years old.
A crevasse formed by melting permafrost (source: Flickr)
There isn’t significant data concerning how we can restore tundra ecosystems, but preserving damaged tundra and protecting tundra from development can keep stored greenhouse gases in the permafrost. Scientists are constantly studying the tundra to learn how to protect it best. It is estimated that the tundra already holds 180 billion metric tons of carbon, which is equivalent to a third of the greenhouse gas in the atmosphere. At the same time, the arctic has warmed four times faster than the rest of the planet in the last 50 years, which has caused permafrost to melt at an astonishing rate. Protecting tundra and restoring tundra ecosystems means we have to limit global warming. The less the planet warms, the fewer greenhouse gases escape from the permafrost. This is a great example of a feedback loop.
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2. Seagrass Meadowlands and Kelp Forests
A look at the rhizomes underneath seagrass (source: Flickr)
Seagrass meadowlands are found in coastal regions around the world. They look like underwater prairies and can extend unbroken for hundreds of miles. Seagrass meadowlands are also incredibly good at sequestering carbon dioxide dissolved in the ocean, which is called ‘blue carbon’. The ocean naturally absorbs carbon dioxide, and studies have found that it already sequesters emissions every year. However, as the ocean absorbs more and more carbon, it becomes more acidic. This is because as carbon enters the ocean, it becomes carbonic acid. Ocean acidification is a problem that threatens wildlife worldwide, with cascading effects, including making it harder for organisms to build shells, and threatening coral reefs’ ability to grow.
Seagrass meadowlands use carbon stored in the ocean to perform photosynthesis and then integrate that carbon into their biomass. When individual seagrass dies, it becomes buried under ocean sediment. Ocean sediment prevents saturated oxygen from reaching the things buried in it and therefore prevents decomposition. Seagrass meadowlands also stabilise ocean sediment and prevent it from eroding, which helps to keep biomass within it from reemitting stored carbon. Frontiers Journal published a study in early 2021 which found that seagrass meadowlands were under severe stress. In the study area in the UK, researchers found that 44% of all seagrass meadowlands had disappeared since 1936 and that 92% of all seagrass meadowlands have been damaged or degraded.
Seagrass meadowlands are also a foundational part of many coastal ecosystems. Fish, birds, and mammals all eat seagrass. The West Indian Manatee, which lives in the Caribbean sea, must eat 50 kg of seagrass daily to survive. Restoring seagrass meadowlands reduces ecosystem pressure on large animals like Manatees, who need seagrass to survive, and whose population has been declining for decades.
In the past couple of decades, the scientific community has not considered the roles kelp forests can play when it comes to sequestering blue carbon, but that is changing. A study published in Nature found that kelp forests sequester a huge amount of carbon yearly, roughly 200 million tonnes. Kelp is a type of macro-algae that grows up from the ocean floor using air-filled nodes to stay upright. When kelp dies, it drifts out to sea, and at some point, the nodes pop, and then the kelp sinks to the ocean floor and is buried. This is the mechanism by which kelp sequesters carbon because once it is buried underneath ocean sediment, the carbon trapped within it doesn’t reenter the ocean.
How kelp sequester blue carbon (source: Harvard University)
But that understates the roles that kelp forests have to play when it comes to the climate crisis and the biodiversity crisis. Kelp is a foundation species, which essentially means that they must be present in large quantities to maintain a healthy kelp forest. Kelp forests are incredibly biodiverse and are home to animals like sea otters, starfish, sea urchins, octopus, seals, sea lions, and a huge variety of fish.
There is precedent for large-scale kelp reforestation around the world, but some of the most successful projects have taken place off the coast of California. In the Santa Monica bay, kelp provides a home for nearly 700 species of animals, but in the last 100 years, 80% of the bay’s kelp has disappeared. Kelp forests are generally threatened by pollution and overfishing. Overfishing removes predators of sea urchins, which feed on kelp roots. When species that eat sea urchins are overfished, then kelp forests can become urchin wastelands.
Kelp forest restoration mirrors land-based assisted natural regeneration methods, where divers encourage kelp forests to regenerate on their own and mitigate populations of sea urchins to help the forest recover more quickly. Projects in the Santa Monica bay are committed to reforesting large areas of the historic kelp forest. Kelp reforestation is also much faster than forest restoration, where forests can take hundreds of years to mature and become established, stable, biodiverse ecosystems. Kelp forests can take as little as one year to completely regenerate because kelp can grow up to three feet per day.
3. Wetlands
The term ‘wetland’ is an umbrella term used to describe a variety of ecosystems. Marshes are a type of wetland that can be found along coastlines or in flat plains. Marshes can occur in fresh or saltwater environments and are periodically flooded or saturated with water. Marsh plants are adapted to grow in these saturated environments; they protect coastal sediments from erosion and can mitigate pollution. Much like seagrass meadowlands, the sediment underneath most marshes has a very low oxygen content, so when plants die and are buried underneath the sediment, the carbon in their biomass doesn’t decompose. Saltwater marshes in particular are incredible at sequestering carbon, but they can serve an even larger role when it comes to reorganizing the way that we participate in ecosystem restoration.
A coastal salt marsh after an oil spill (source: Flickr)
It is estimated that the United States loses 24,000 hectares of saltwater marsh every year. Saltwater marshes can mitigate storm surges and damage from sea level rise, so when they are filled in, drained, or damaged, a positive feedback loop is established, which encourages further degradation of saltwater marsh ecosystems. By reintegrating saltwater marshes into coastlines around densely populated areas, we can make cities more resilient when it comes to extreme weather, and sea level rise.
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Peatland bogs are another type of wetland ecosystem. They accumulate over millions of years and store carbon remarkably well. Peat grows upwards on top of dead plant matter, and peat moss at the top of peatlands prevents oxygen from reaching biomass below it, preventing decomposition and sequestering carbon. It is estimated that peatlands already hold about a third of the carbon sequestered in soils worldwide, peatlands hold 550 billion tons of carbon, but peatlands around the world are under threat. Some peatlands have been drained and replanted with trees in an attempt to establish tree plantations for paper and wood mills, while other peatlands have been damaged by peat harvesting or development.
When peat is damaged, the carbon stored in the dead biomass underneath the living layer becomes exposed to oxygen and begins to decompose and rerelease carbon into the atmosphere. Preserving and rehabilitating peatlands is vitally important to keep that carbon in the ground. At the same time, countries with peatlands around the world, like Scotland, Canada, and Russia, have done some work to restore and replenish damaged and drained peatlands. Reestablishing peatlands takes a long time, but in the long run, peatlands have enormous potential. Peatlands only take up 3% of the earth’s surface, and even though they mature over thousands of years, a rehabilitation project in Canada found that a restored peat ecosystem began sequestering carbon after only three years.
4. Mangrove Forests
A mangrove restoration project in Timor-Leste (source: Flickr)
Efforts to restore mangrove forests are often tarnished by some of the same problems that dry forest restoration projects face. Mangrove forests should be biodiverse and have more than one species of mangrove, yet most restoration projects plant vast monocultures of mangrove trees. Mangrove forests can be planted in almost any tropical or subtropical coastal area and can grow in sandy, or rocky substrate. After only a few years, a new mangrove forest can sequester a lot of carbon. Mangroves naturally produce a layer of sediment that, much like saltwater marshes, prevents oxygen from reaching biomass that falls into the sediment. At the same time, mangrove forests are incredible at preventing damage from extreme weather and storm surges because they absorb tidal and wave energy.
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Conclusion
Assisted natural regeneration holds enormous potential for us as we reconsider what it means to sequester carbon by restoring ecosystems. We have the incredible opportunity to expand restoration to all types of ecosystems, and not just forests. The climate crisis, which is a result of destructive human activities, has impacted every ecosystem on earth, and so restoring ecosystems is a unique form of reparation. Tundra, seagrass meadowlands, kelp forests, wetlands, and mangrove forests are all amazing at sequestering carbon, and providing habitats for a diverse array of animals. Expanding our concepts of reforestation to these ecosystems is essential to rethinking the role of reforestation in solving the climate crisis.
This is the first part of an article about reforestation and ecosystem services, you can read the second part here.
