A novel tree nursery gives the Caatinga a fighting chance against desertification
- Nearly half of the Caatinga, the only exclusively Brazilian biome, has been destroyed and 13% of its territory has already been lost to desertification.
- A project at Rio Grande do Norte Federal University is using PVC pipes to lengthen and accelerate root growth in native plant species that have trouble drawing water from degraded soil.
- Previous restoration methods in the Caatinga resulted in mortality rates near 70% after transplant, but this new method reverses that figure, raising survival rates to 70%.
The Caatinga is the most densely populated semiarid region in the world and the only exclusively Brazilian biome. The region needs assistance to prevent it from becoming an immense desert.
Nearly half of the Caatinga has already been destroyed — some 840,000 square kilometers (324,300 square miles) — and there are indications that this symbol of resilience — home to diverse and endemic species — is undergoing a desertification process that has already consumed 13% of its territory.
The Caatinga is home to plants that have adapted to seasonal rainfall extremes, like the iconic umbu tree (Spondias tuberosa) that stores water in its roots. But the biome can no longer rely solely on evolution and the peculiar transformations of its vegetation to survive as it comes up against deforestation and global warming.
But one simple and innovative idea from the Restoration Ecology Lab at Rio Grande do Norte Federal University’s Ecology Department could turn the tables on failed Caatinga restoration projects, in which 70% of the seedlings transplanted by traditional methods are often lost
The method developed at the UFRN lab has reversed that, raising survival rates to 70% on average. It uses PVC pipes to accelerate and lengthen root growth in native plants that have difficulty drawing water from degraded and salty soil.
From pasture to forest
In the first management phase, the seedlings are germinated in a greenhouse inside PVC pipes with small bags of water at the base, a system that draws the roots downward. The roots can grow to a meter in length within two months, after which the plants are taken to a deteriorated area inside Açu National Forest, located in the dry inland region of the state of Rio Grande do Norte. Once the tree is planted, the tube is removed and reused to grow more seedlings.
Reforestation using this method has proven surprisingly successful on a large scale. Natural regeneration had been impossible in a 3.5-hectare (8.6-acre) test area that had been used as pasture for decades and later abandoned for nearly 15 years. But five years after the start of a 2016 restoration project, 4,704 plants have transformed it into a diverse forest attracting wildlife and reviving the ecosystem’s hydrological function.
Gislene Ganade is the coordinator of this restoration project and was recognized by the 2015 United Nations Dryland Champions program during the first year of the experiment. She says the strategy is efficient because the plant is placed into nature with a well-developed trunk, leaves and roots, already able to sustain itself. Because it is robust, the plant can take on field stress with large reserves of glucose, starch and water, allowing it to subsist until the next season’s rains.
“One very interesting thing about this technology is that we are accelerating the plant’s growth inside the greenhouse, giving it as many resources as possible to prepare it for a more critical field situation,” Ganade says. “When it is transplanted, it is the size of a 2-year-old plant, not just a few months old. And then, the evolutionary history of the Caatinga plants takes care of itself.”
Another factor that makes the new method more effective is the use of facilitator plants, also known as nurse plants, which can improve the quality of the soil by fixing nutrients and redistributing water to benefit more fragile species.
According to Ganade, who earned her Ph.D. in ecology at Imperial College London, the process of desertification is caused by a combination of factors. These include salinization of the topsoil due to poor irrigation with brackish water; the cutting and burning of vegetation for wood and brick and roof tile production; and trampling of vegetation by cattle and goat herds.
“The exposure of eroded soil with no vegetation to the sun causes the extreme heat to pull water up from the depths, bringing with it the salt from the lower layers of the earth,” Ganade says. “And a salty surface has a great deal of difficulty establishing plant life because the salt competes with the plants for water, even when it rains.”
Ganade says one of the challenging parts of a successful Caatinga restoration project is to create more environmentally protected areas by using information on how native plants will respond to climate change and rising temperatures.
“Some plants will change their addresses. Imagine the consequences of this for restoration,” she says. “You can restore it today but it’s possible that 70 years from now, the plant will disappear from that place. The climate could change in such a way that it can’t live there in the future.”
In Catimbau National Park, in a dry stretch of the Caatinga in Pernambuco state, a team from Pernambuco Federal University’s Botany Department has been using the PVC pipe method that Ganade created to slow degradation of the land and keep it from becoming desert. Project coordinator Felipe Melo, a professor in the department, credit’s Ganade’s work and says the objective is to use restoration as a tool to promote hydrological function and energy and food security for the people living in the remote countryside of this dry region.
“The Caatinga was degraded before local human development could take place,” he says. “We are trying to understand the role that restoration can play in making life more secure for the people living there, like providing access to water. Incidentally, this is associated with taking care of natural springs. We are also testing plant species that provide firewood, which is an important energy source, and also plants that are food sources, like grass for goats.”
Ganade says the success of the Açu National Forest restoration project points to the Caatinga’s own capacity for survival: “The biome seems difficult to restore, but it responds quickly. That’s how it evolved over time, by responding quickly to the rains because there are many nutrients stored in the soil.”
Banner image of sunset in Açu National Forest, in Brazil’s Rio Grande do Norte State, by Gislene Ganade.
This story was first reported by our Brazil team and published here on our Brazil site on April 14, 2021.