Technology

Indiscriminate tree planting devalues ​​savannahs, not restores them.

Text: José Tadeu Arantes, Agência FAPESP

Savannah is not a degraded forest. And you don’t restore the savannah by planting trees. These claims, made for some time by leading researchers on the subject, were repeated in a special issue of Science published earlier this month. The topic has become even more relevant as the United Nations (UN) has designated the period from 2021 to 2030 as the “United Nations Decade of Ecosystem Restoration”. However, some projects to this end ignore the characteristics of complex biomes, such as savannahs, and try to make indiscriminate tree planting a kind of cure-all.

“There are many degraded forests in the world. But this concept does not apply to savannahs. And the expression “savannization”, used, for example, in relation to the cut areas of the Amazon, becomes an inappropriate term that hinders rather than helps. Because, unlike degraded forests, savannahs are very old biomes, complex and rich in biodiversity,” says ecologist Alessandra Fidelis, professor at Universidade Estadual Paulista (Unesp) and co-author of the paper.

“We are in a decade of recovery and the conservation and restoration of savanna-type ecosystems is urgent. But how to restore them? Planting trees is not an option. It seems that these environments have appeared recently and are simple. However, tropical savannas, for example, have been around for millions of years. And they are of high complexity, both in their above-ground component, formed by a continuous herbaceous layer, rich in species of cereals and forbs, and in sparse shrubs and trees, and, mainly, in a large underground functional diversity formed by roots and underground organs of the reservation. It is these organs that give the system stability, as they have reserves, and also store the kidneys, which turn into new branches after, for example, a site fire. We still don’t know how to restore it,” adds Fidelis.

The researcher reports that C4 grass, which is part of the grassy stratum, appeared 25 million years ago. And that the savannas spread over vast areas of the planet 10 million years ago. “Most of the species that make up the savannas were selected and evolved as a result of disturbances such as fire and herbivory. It’s not something that can be restored at the snap of a finger. If this vegetation burns down, for example, it will quickly sprout again. But if the underground organs and roots are uprooted by agricultural machinery, regrowth is impossible. There are savannahs that were devastated over a century ago and still have not recovered,” he says.

threatened by cerrado

This consideration is especially important in Brazil because the Cerrado, the most biodiverse savannah in the world, is disappearing every day under the pressure of large-scale farming. Its survival is even more dangerous than in the Amazon rainforest.

Fidelis says grasslands and savannahs, commonly referred to as “old-growth grasslands” in a Science article, cover at least 40% of the Earth’s surface. These are ecosystems that form open landscapes, consisting mainly of cereals, grasses, shrubs and small to medium trees. They are distributed over 27% of the territory of Brazil and dominate four of the six existing biomes of the country: Cerrado, Caatinga, Pampa and Pantanal. But they also spawn in two other biomes: in the Campinaran, in the Amazon, and in the fields above the mountains, in the Atlantic Forest.

Thanks to their rich biodiversity, these grasslands and savannahs provide direct “environmental services” to more than 1 billion people on the planet. But in Brazil its importance is even greater, because the Cerrado is the only savanna in the world with perennial rivers and the birthplace of some of the country’s most important rivers – the Xingu, Tocantins, Araguaia, San Francisco, Parnaiba, Gurupi, Jequitinhonha, Parana and Paraguay, among others.

It is never superfluous to remember that 77.2% of Brazil’s electricity matrix comes from hydroelectric power. And that the country has the third largest technically viable hydropower potential in the world. The degradation of the Cerrado River endangers this fabulous energy resource and threatens the supply of fresh water for human consumption and agricultural activities, while the climate crisis has made water one of the world’s most valuable commodities. , planet.

“In the face of escalating destruction, it is only natural that people have hopes for recovery. But you need to be very careful with this, because many projects confuse restoration with simple tree planting. And this clumsy planting poses an additional threat by creating artificial forests in savannah ecosystems. For example, almost 1 million square kilometers of grasslands and savannas in Africa have been identified as targets for tree planting by 2030, ignoring their specificity and their value in terms of biodiversity and ecosystem services,” Fidelis muses.

He continues: “The unique characteristics of these ecosystems, combining high complexity, diversity of both aerial vegetation and subterranean components, resilience to disturbances such as fires and herbivores, all of which have evolved over millions of years, make recovery very difficult. The degradation that destroys the gem bank and underground facilities could cause irreversible damage.”

The researcher highlights three important points that should be considered in long-term projects for the restoration of these systems. First, most species re-sprout, i.e., depend on the presence of underground structures with supplies and a bank of viable buds. Does not regenerate by germination. Therefore, the importance of the gem bank and underground facilities cannot be underestimated.

Secondly, the restoration of these ecosystems is not fast and requires careful control, as there are problems with biological invasions (for example, exotic grasses such as brachiaria) or even with wood compaction, which can completely change the course of restoration. .

Thirdly, and finally, feedbacks between soil, vegetation, fire, and herbivores are extremely important in these ecosystems. The relationship between these terms changes over time. And you need to understand how it works, what needs to be done to support it and when, if necessary, to promote it. For example, due to reasonable fire control.

“The important message is that we must guide the restoration of these ecosystems based on the characteristics of what we call old-growth grasslands, i.e. primary grasslands and savannahs. These complex systems, from a functional point of view, were created by nature over millions of years. You have to learn from nature,” concludes Fidelis.

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The researcher has already coordinated several Cerrado management projects supported by FAPESP. He currently leads the project “Using Adaptive Management to Optimize Long-Term Management of Invasive Species Harmful to Biodiversity and Rural Economy”.

The article “Ancient Grassland Determines Pasture Restoration Goals” can be found at: www.science.org/doi/10.1126/science.abo4605.

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