Regrowing lost trees: How seeds might repair our climate

Of all the possible solutions to mitigate climate change, planting trees is quite an appealing one. Not only can it help to naturally remove carbon from the atmosphere, it can help to improve biodiversity and repair damaged ecosystems, and make our planet a more visually attractive place to live.
 
This has led to a rise in reforestation schemes that allow consumers and corporations to offset their carbon emissions by paying to plant more trees. But some of the benefits of these schemes are contentious.
 
Some of the criticisms level that there isn’t even enough available space to add this many trees, and that land use changes are not factored in (the land that those new forests would be grown on might already have plants growing on it, sequestering carbon, or be carbon-rich ground, like peatlands).
 
Measuring carbon sequestration has its technical challenges
 
The variation in claims about the carbon sequestration merits of replanting forests arises from the fact that there is always uncertainty when estimating the carbon stored in trees, says Victoria Meyer, a carbon scientist at Terraformation, a forest restoration company. The only way to measure the carbon in a tree is to cut it down and weigh it, she says, which would somewhat defeat the point.
 
Instead, carbon scientists like her make estimations based on real measurements of the same species of trees in the past which are then used to create models of current and future forests.
 
The more diversity of species in a forest, the more data is required to make estimations. For current forests, Meyer would identify the species, with the help of a botanist, in a 50m by 50m plot and extrapolate that data out across the whole forest area. The more variation in the forest, the more plots are required to make an accurate sample. Lidar data from drones, planes or satellites can then be used to make even more accurate estimations. This data can be used to precisely measure the height of trees. “It's faster, it's cheaper, and in most cases, it's more accurate because Lidar measurements are really, really accurate,” says Meyer.


 
But every forest is unique, which means estimates vary from forest to forest. Even a few kilometres away, where a forest might have a very similar composition of species, the results might be different. The rate of precipitation, elevation, and the amount of sunlight will be a bit different. “And that's going to have an impact on how much carbon is sequestered,” says Meyer.
 
Where is it best to grow trees?
 
Regional variations like this are the reason climate scientists are interested in the best places to plant trees. Generally, “the wet tropics are the best place to plant because you have more biodiversity,” says Meyer. Whereas trees planted near the poles, for example, are less effective as they grow more slowly. But forests in the tropics are most affected by climate change and the lack of water.
 
Understanding the role forests play in climate dynamics is important too. Trees affect local microclimates, increasing humidity, which can have negative climate effects. Some trees release volatile compounds which can act as greenhouse gases.
 
From a biodiversity point of view, planting local, native species is essential if the ambition is to create a long-lasting forest. “What really matters is which tree it is, where it is and is it helping the local community or not,” says Meyer.
 
One example of this comes from Terraformation’s Pacific Flight site at Kaupalaoa, located on the Kona side of Hawaii. Once a native sandalwood forest, it is “essentially now a desert,” says Marian Chau, head of seed banking at Terraformation. “There's a little bit of dry grass and shrubs and that's it.” The Terraformation team are working to restore native species that would have once been found in that ecosystem using seeds and plants sourced from their seed bank.
 
Growing a new forest, or replacing one that we have lost, is not as simple as scattering seeds on the ground. What we plant, and where we plant it has a big impact on the success of reforestation. Some reforestation schemes have been criticised for growing monocultures, or non-native species.
 
“It's really critical to collect seeds locally, because local native species are going to be well adapted to the conditions in that area. And it makes for a more resilient forest,” says Chau. “If you take a species that's not native and plant it in a new environment, often it might actually become invasive.”
 
That's something which has happened over and over again in Hawaii, says Chau, where previous attempts to revegetate the land have resulted in non-native trees like eucalyptus and strawberry guava becoming seriously invasive, threatening the native species. As an isolated island, Hawaii’s terrestrial fauna and flora are incredibly biologically important. Around 90% of the species of Hawaii’s flowering plants are found only here. In some instances, there are species on the island which number fewer than 50 individual plants, says Chau.
 
The seed banks
 
You might have heard of seed banks in the context of preserving genetic material for generations to come, from which wild populations could be reintroduced should they ever go extinct. The objective of these “doomsday vault” seed banks, like the one in Svalbard, Norway, is to have specimens of every seed available. But for reforestation projects, seeds might only need to be stored for a few years, and it is more important to have the right species and enough seeds, says Chau.
 
A new restoration project might begin years in advance of the first tree being planted to ensure there is enough supply should a wildfire, storm or other emergency cause a setback.
 
“If you just try to collect seeds and plant them immediately you're limited to whatever you can find at that moment,” says Chau. “And there's often times where if there's bad weather in one year, you might not get the seeds at all from a certain species and then you might be forced to kind of compromise on biodiversity.”
 
Terraformation's unique approach is to start reforestation projects using their portable, shipping container seed banks. Seeds can be collected, processed and prepared for planting in an off-grid lab. This makes it much easier to have the right seeds on hand and on-demand.
 
“It's designed so that you have everything inside that you need to get started with seed banking right away, and it can be deployed in remote areas where it might not be feasible to build an entire building to have a seed bank,” says Chau. Terraformation also offers a build-your-own seed bank kit with instructions, or just the equipment for projects where a building is already available.
 
Inside the container the temperature and humidity can be controlled, which is critical for seed banking for anything more than the short-term. Seeds are stripped of their fleshy fruits or dry husks and dehumidified so they can be frozen without being damaged.
 
“If you're restoring a native ecosystem you must collect wild seeds sustainably, making sure you have access to those seeds, and then finding the seeds at the right time and collecting them when they're ripe,” says Chau. She adds that Terraformation is focused on restoration, but they also support conservation work to ensure that species have a future.
 
“Seed banking is a technical skill that requires some training, so we are providing Terraformation Academy, which is our online course that helps give people the background,” she says. “And then we're also going to support them through our virtual training program once they get seed banks.” Seed bankers must record the location, species, and date of when seeds were collected, which requires training. It's important not to take more than about 20% of the seeds on a plant or in a plant population at a given time to preserve the wild population, she says.
 
Working to train local communities in the value of seed banking also excites Meyer. “I can really see that our work is actually having an impact on people and the planet,” she says. “The thing that excites me the most is the possibility to go on a very large scale. If we manage to do that, it's going to be a game changer.”
 
While the importance of seed banking projects is clear to Terraformation, as Meyer highlights, the areas of the world that would benefit most from protecting and restoring forests are often some of the least developed, which means funding can be an issue.
 
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