- In Argentina’s Neuquén province, local laws require that when oil companies decommission a drilling site in the Monte Desert, they dig furrows across the site to promote plant growth, a form of assisted natural regeneration (ANR). However, research has never tested its effectiveness until now.
- A study that compared 16 of these sites with undisturbed desert found that after five years, restored sites still had much lower plant density, diversity and plant coverage. However, the researchers were surprised by the relatively high number of species at the sites and by the unexpected success of certain plant species.
- Experts say that future research should focus on the microbiome in these soils, which plays an important role in desert plant communities, and more active efforts that complement passive techniques like ANR.
For a plant, life in Argentina’s Monte Desert is hard enough. Daily temperatures can fluctuate dramatically; it rarely rains, and there are few nutrients in the parched soil for a hungry plant. To add to their struggles: Across this desert, a long history of oil drilling and a new boom in fracking have left hundreds of sites where plants have been completely wiped out, and the soil replaced with trucked-in, densely compacted dirt. When those drilling sites go quiet, plants often struggle to recolonize the places they once lived.
In a 2024 study, researchers from the National University of Comahue examined whether a technique required by the local government to aid restoration helps plants regrow at these former drilling sites. They found that the technique, a type of assisted natural regeneration (ANR), is a bit of a mixed bag: The restored sites still had much lower plant density, diversity and plant coverage when compared with undisturbed sites. However, about 40% of the species that might be found in an undisturbed site were present in the ANR-remediated sites, including some species the researchers didn’t expect.
“We were surprised,” says primary investigator Florencia del Mar González, a researcher at Comahue’s Laboratory of Rehabilitation and Ecological Restoration of Arid and Semiarid Ecosystems (LARREA). When looking at satellite images before their fieldwork, del Mar González and her team saw little regrowth at the former drilling sites. However, when they went into the field, “we began to find some response from the ecosystem in some of the places we were visiting,” she says. “So, there, we said, ‘Well, what’s going on here?’”
Assisted natural regeneration is an umbrella term for a group of relatively “passive” practices, which focus on enhancing the conditions that encourage natural plant growth, rather than more intensive (and expensive) processes like reseeding or replanting. In Neuquén province, which contains a small fraction of the Monte Desert, the local government has required oil companies to complete ANR at decommissioned drilling sites since 1999. It’s a compelling intervention because it’s relatively cheap and simple: Companies are required to plow 15-centimeter- (6-inch-) deep furrows across the compacted site, where water can collect and young plants can shelter from harsh conditions — giving those plants, in theory, an extra advantage in re-colonizing the site.
But these techniques were never tested in the Monte before being required of oil companies.
“Many of the recommended practices are adopted from other countries, sometimes even from other ecosystems,” says del Mar González. As part of her doctoral thesis, she decided to test just how effective ANR was at encouraging plants to return to these degraded sites.
She selected 16 scarified former oil-drilling sites that had been abandoned for five years, visiting each to collect soil samples and survey the plants that had regrown there. She also conducted the same tests on neighboring areas that had been undisturbed by human activity as ecological reference (ER) sites.
Her findings suggest that this ANR technique could help with species richness, or the overall number of species found at a site. She cataloged 15 different species across the former drilling sites, about 40% of the number found at the ER sites (38). These included some species that had previously been characterized as “climax” species, such Larrea divaricata and L. cuneifolia, small, flowering evergreen shrubs related to creosote, which are normally found in stable, fully regrown ecosystems. L. divaricata, found in 81% of the degraded sites, is also known as a “nurse” plant for its ability to improve soil moisture and provide shade to seedlings, paving the way for other species.
Yet plant coverage was still a massive 12.5 times lower in degraded sites than in the reference sites, and species diversity, which accounts for the abundance of different species, at the degraded sites was only about 16.6% of that at the ER sites.
James Aronson, an senior scientist emeritus at the Missouri Botanical Garden who has focused much of his research on the restoration and rehabilitation of arid and semiarid ecosystems, says the paper is an excellent first step — but “the next step is to study what is going on underground.
“If you want to do arid land or dryland restoration, you have to pay a lot of attention to what’s in the soil,” Aronson says. Because desert plants usually face extremely poor nutrient availability, many have developed symbiotic relationships with microbes and fungi to survive. These microscopic communities would have been entirely removed when the oil platforms were built, leaving local plant communities without their natural partners as they try to recolonize.
Even with a functioning soil microbiome, Aronson emphasizes that the extreme conditions of a desert also mean plant growth tends to happen very, very slowly. “In the first 10 years of a successful project, you might not see anything unless you take soil samples and put them under the microscope — and even longer, 20-30 years, to really see action in the above-ground parts of the ecosystem,” he says. In that light, even the small recovery that del Mar González observed may be significant.
Aronson is currently collaborating with Daniel Roberto Pérez, the director of LARREA and del Mar González’s co-author on the ANR paper, on a project investigating the microbiota composition of healthy soils in the Monte desert — research that could help future restoration efforts to rejuvenate these invisible communities. And del Mar González and her colleagues are also working on a paper on experiments introducing nurse plants to ANR-modified sites, to see if they can improve colonization. These more active interventions could be essential for degraded ecosystems that are under more pressure than ever before.
“Facing humanitarian crises, plus climate change, plus species extinction crises … we need to be working on active restoration, in drylands as well as everything else,” Aronson says. “If you want to do more than pocket handkerchief-sized efforts, or symbolic, greenwashing efforts, we should be investing heavily in the full spectrum, from passive to active interventions.”
Already, del Mar González thinks her research into ANR in the Monte has yielded at least one actionable result: She and her colleagues say they believe the furrows on these oil-drilling sites should be deeper than the required 15 cm, to provide more water retention and slightly cooler temperatures than the surrounding soils. But she also says the work she’s doing in the Monte could be helpful beyond the desert’s extremes, to human-degraded environments all over the world.
“At the end of the day, an oil esplanade is a cleared area without vegetation cover, with soil damage and compaction,” del Mar González says. The same sort of damage can occur when humans build a road, she explains, and the same sort of recovery may be needed if that road is abandoned.
“When you want to develop any infrastructure, these environmental impacts are generated,” she says. “So, we are always thinking about methodologies and work strategies to increase the scale of recovery.”
Banner image: Soil variable sampling. Credit: Florencia del Mar Gonzalez.
Citation:
Del Mar González, F., & Pérez, D. R. (2024). How much can assisted natural regeneration contribute to ecological restoration in arid lands? Land Degradation & Development, 35(14), 4163-4172. doi:10.1002/ldr.5212
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