Rebuilding damaged ecosystems is a fraught enterprise. Replanted trees die. Artificial wetlands fail to store as much carbon as their natural counterparts. Species don’t always return to repaired habitats. It’s a lot easier to break an ecosystem than to put it back together.
New research suggests that transplanting layers of soil from pristine land could increase the chance of success.
“People usually only look at aboveground recovery,” said Jasper Wubs, an ecologist at the Netherlands Institute of Ecology who coordinate the work. “We have demonstrated that the groundwork for success is laid below ground.”
The complex interconnections between plants and soils have become more apparent in recent years, with insights into the important roles of soil microbes, such as underground fungal networks dubbed the “wood wide web.”
In earlier research in the Netherlands, Wubs and colleagues found that adding a relatively small amount of soil from either grasslands or heather increased the amount of microbes in the soil of old farmland and steered recovery so that it more closely resembled the ecosystems from which the soil came. But did the results in a Dutch field translate to, say, land in a former tropical jungle? Wubs and a team of researchers from Europe, South and North America and Australia wanted to find out.
The scientists compiled data from 46 previous experiments in 17 countries on four continents that tested different strategies for restoring vegetation in degraded habitats. In these experiments, scientists tried various measures including planting seeds, spreading vegetation that contains seeds over the ground, taking topsoil from intact ecosystems and sprinkling it across the damaged area, and, in the most dramatic version of a soil transplant, scooping up sections of intact land like so much carpet and installing it in a restoration site.
The results showed that in many cases, importing soil as well as vegetation helped give restoration a boost. Land with transplanted soil wound up more closely resembling the native habitat from which the soil came—by an average of 40% compared to just spreading seed-bearing clippings over the restored land, according to a paper published this week in the Journal of Applied Ecology.
The new findings mean “that we are now better able to restore biodiverse ecosystems in places where natural regeneration is not enough,” said Wubs.
Researchers point to several factors that might contribute to the improved performance. The soil transplant brought over not just mineral dirt but microbes, seeds and plants with more intact root systems.
Several other elements contributed to success. Transplants tended to make more of a difference in loamy soil—a mix of sand, silt and clay that is prized as prime gardening soil. They also fared better when applied to areas bigger than 180 square meters, slightly less than half a basketball court.
Getting a successful start also proved vital. Places that initially showed progress toward growing native vegetation continued on that trajectory over time, suggesting that as native species took over it helped encourage a cycle of further recovery. Meanwhile, land that initially showed little recovery continued to move away from the target ecosystem, creating what the scientists dubbed “misfits.”
But before breaking out the champagne, the work also delivered some sobering results. The restored areas were only pale imitations of the real thing. At the end of experiments, even land that got an injection of fresh soil and vegetation only came within 40% of the vegetation community found in the comparable natural lands.
The benefits of full-scale soil transplants might also not measure up to the costs, the scientists warned. Such projects are expensive and can exact a toll on the donor landscapes where the soil and vegetation is dug up. On a large restoration site, or a place where the goal is to simply cover an area with greenery, it might not be worth it.
In other places, where the goal is to recreate an entire plant community, a transplant might be the ticket. If it will work. “We need to figure out why restoration is more successful in some cases than in others,” said Wubs. “The glass is half full, but it could be fuller.”
Gerrits, et. al. “Synthesis on the effectiveness of soil translocation for plant community restoration.” Journal of Applied Ecology. Feb. 12, 2023.
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