- Almost half of Brazil’s Cerrado savanna has been deforested, and restoration proposals now center largely on planting trees in the degraded areas.
- However, as a grassland, and not a degraded forest, restoring undergrowth and some bushes would be the best option for recovering it, experts say.
- Reforesting the Cerrado with trees would change the biome’s core traits, alter its biodiversity, and impact the availability of groundwater.
- The Cerrado is able to regenerate itself, even after fires; the challenge lies in recovering native vegetation after agricultural use, especially the industrial farming of monoculture crops.
When it comes to environmental destruction in Brazil, the world’s focus tends to be on the deforestation and burning of the Amazon. Yet the Cerrado, the second-largest Brazilian biome, at 2 million square kilometers (772,000 square miles), is being silently destroyed. Today, only 54.4% of the region is still covered with native vegetation, and a much smaller proportion (around 20%) remains untouched.
This has prompted several proposals from well-meaning conservation activists to recover the Cerrado by planting forests. That, however, would be a mistake, experts say: the Cerrado is a savanna, and a savanna is not a degraded forest.
Forestry engineer Giselda Durigan, from the ecology and hydrology lab at the São Paulo state Environmental Research Institute, says the idea of “recovering a degraded area” must be preceded by defining what “degradation” means in the first place.
“For savannas and forests, this term has varied definitions,” she says. “Degradation conditions are very different in the Cerrado, and restoration challenges will also be different for each of them.”
The process of humans occupying and therefore changing the Cerrado intensified at the turn of the 1950s to the 1960s, with road and rail construction bringing migrants to the region from across Brazil. They were attracted by the government’s development-driven farming policies aimed at integrating the Cerrado into the rest of the country, thus creating the conditions for expanding commercial agriculture.
The result is the current state of degradation of nearly half of the Cerrado. To make matters worse, the areas that haven’t yet been cleared are fragmented and under deforestation pressure for conversion into yet more agricultural land. Protected areas such as national and state parks and biological reserves cover just a fraction, 2.85%, of the Cerrado and don’t represent the full diversity of its various ecosystems.
Trees would change the biome
Given this situation, there’s a widespread perception that the solution to helping the Cerrado recover is to plant trees.
“That’s not an option,” says Alessandra Tomaselli Fidelis, an ecologist at São Paulo State University’s (UNESP) Institute of Biosciences. “The region’s savanna and grassland ecosystems are made up mostly of heliophytic species, that is, those that like sunlight. The main components of these environments are grasses and small plants, some bushes and few trees.”
When trees are planted as a restoration method in areas that were previously grassland or savanna, they alter the environment. In the case of the Cerrado, they purge the native vegetation, most of which is herbaceous undergrowth. Forest plantations cast a lot of shade, and in open grasslands like the Cerrado, this prevents the return of undergrowth species.
“I always compare,” Fidelis says, “when we restore forests, we plant trees, right? We do that because trees are the most important element of a forest. The same happens with grassland and savanna ecosystems — the most important elements in these environments are grasses and small plants, not trees.”
Durigan says there are several common misconceptions among people in general, and even scientists, who, for example, think that a burned patch of Cerrado is “degraded” land. Not so, she says. An area with typical savanna vegetation isn’t degraded by fire. It will naturally restore itself in less than six months, because it has evolved over millions of years to survive fires — even frequent and intense ones — and has undergone this kind of recovery countless times.
So even if tree trunks and branches burn, the Cerrado will still be the Cerrado, and the plants that don’t like shade will benefit, Durigan says. “But this doesn’t apply to habitats that are vulnerable to intense fires such as peat bogs and swamp forests, where fire can cause dramatic destruction of organic soils,” she says.
The challenge of restoring cropland
When Cerrado areas do become degraded, by conversion for agriculture, it becomes very difficult to restore them — especially open land such as grasslands and savannas. Recovery will depend strongly on the type of degradation. For example, in an area converted for growing crops, where the soil has been plowed or turned over, there’s a high chance that underground components of the native vegetation, such as the root nodules, have been destroyed. It’s these components that would otherwise guarantee the biome’s regeneration.
Fidelis says restoring Cerrado from farmland is the most difficult case because it demands active restoration actions. “When a degraded area is covered by invasive species, mainly grasses, we have another major problem, which is controlling them first, and then thinking about restoring these environments,” she says. “As you can see, restoring these savanna and grassland areas is very difficult, and we still know little about it.”
Compounding the difficulty is that there are several types of degradation in the Cerrado, such as areas converted for growing crops, especially soy, corn and sugarcane. This is the most dramatic of all types of degradation because it causes total loss of biodiversity by destroying native plants and their regrowth structures, as well as soil microorganisms. It also drives profound changes in environmental conditions, with soil breakdown and changes in water infiltration capacity and chemistry as a result of the use of fertilizers, herbicides and pesticides, often resulting in erosion and siltation.
The problem is that Cerrado vegetation can’t be restored after the land has been used for farming. Few native species are capable of germinating, surviving and thriving in the environmental conditions left behind by agriculture. “So, seedlings or seeds of generalist species have often been planted to restore tree cover, which in no way resembles the savanna that used to be there and even less its species makeup,” Durigan says. “You can call it revegetation or rehabilitation, but not restoration.”
Last, but no less serious, is the degradation caused by forest plantations. “In the Cerrado, the biggest impact of this land use is reducing the amount of water that infiltrates — up to 30% is retained in the forest canopy — and increasing extraction of groundwater by the trees,” Durigan says. “As a consequence, the water table is lowered, and river flows decrease.”
In this case, the only way to restore the area is by removing those trees to allow the hydrological processes to return to normal. Regeneration of tree species usually occurs naturally in Cerrado areas, and planting trees isn’t necessary. “As with pastures, the undergrowth stratum does not regenerate [where trees are planted], and exotic grasses tend to reoccupy the area, so restoration challenges are virtually the same,” Durigan says.
Restoration projects are rare
Fidelis says there are several challenges to restoring the Cerrado. Many people confuse open ecosystems — fields and savannas — with degraded areas, which they’re not.
“The first challenge is learning to define what a degraded ecosystem really is — and grasslands and savannas are not degraded forests,” she says. “Yes, there are degraded fields and savannas, and one of the challenges is that we still don’t really know the best techniques for restoring these environments.”
It’s often possible to revegetate areas, cover them with native species, but there’s still a long way to go to recover the resilience of these environments. “Another difficulty is access to seedlings of grasses and other small plants, in addition to controlling invasive species, mainly grasses,” Fidelis adds.
Larissa Gabriela Araujo Goebel, a biologist at Mato Grosso State University, says that in order to recover the Cerrado, its biodiversity and the services it performs must also be restored.
“It’s important to recover the local fauna, since a large part of the region’s plants depend on seed-dispersing animals, as is the case with fruits with large seeds,” she says. “Therefore, acting to conserve wildlife such as birds, tapirs, primates, bats and others can help recover degraded areas, enabling native vegetation to thrive.”
But due to all the difficulties, very little of the degraded savanna area has been recovered.
“Successful restoration projects are rare, except for those that were carried out on an experimental basis,” Durigan says. “In the Central Plateau’s Chapada dos Veadeiros [National Park], there are important initiatives, especially aimed at restoring rural physiognomies. But there are also disastrous examples of trees planted where vegetation used to be intact natural grassland or savanna.”
Banner image: Trees planted on farms in Brazil’s Federal District. Image courtesy of Wenderson Araujo/CNA.