Prof. Liliana Dávalos - Half of Burned Forests Across Latin America Do Not Survive

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https://news.mongabay.com/2021/08/half-of-burned-forests-across-latin-america-dont-survive-study-finds/

Researchers monitored the forests of 22 Latin American countries from 2003 to 2018, and analyzed their resistance to fires.

The fragility of Latin American forests has been demonstrated by a pioneering study published in the journal Science Advances, which reveals an alarming finding: half of the region’s forests would not survive after their first fire, much less withstand a second conflagration in less than five years.

The research was led by researchers at the National University of Colombia and evaluated the catastrophic consequences of forest fires in 22 Latin American countries in the 15 years from 2003. The study also involved scientists from Chile, Spain and the U.S.

The researchers focused on the 16 countries with the highest rates of loss, with Paraguay (8.4%), Guatemala (7.84%), Honduras (6.13%), Belize (3.63%), and Mexico (3.40%) topping the list for the highest proportion of burned forests in 2003.

Lead author Dolors Armenteras, a member of the Landscape Ecology and Ecosystem Modeling (Ecolmod) group at the National University of Colombia, says the goal of the research was to examine what happens in the long term to forests after a fire. That way, they could generate a diagnosis of the vulnerability of these ecosystems, understanding it as the percentage of plant biomass that gets lost after a single fire, and their potential capacity to recover.

The scientists monitored forests that burned without prior logging to open pasture. According to Armenteras, the researchers wanted to include a larger sample of forests than is usually found in this kind of study, which typically only have data from countries in the Amazon Basin, especially Brazil.

To achieve this, they used land cover maps for Latin America since 2001 and monthly observations of burned areas with the help of NASA’s Modis satellite instrument from 2003 to 2018.

Fires a concern in all countries

They estimated that, in 2003, approximately 8.5 million hectares (21 million acres) of forest in Latin America, equivalent to 1.1% of the region’s area, suffered at least one fire. Once they had identified those burned areas, the researchers looked at their records all the way up to 2018.

They concluded that the first five years after a fire are critical, since half of the forests studied were lost in that period. The other half of the burned forests caught fire up to two or three times more, which completely degraded them.

“We noticed that if a second fire occurs in five years, the consequences are devastating for the forests and their biodiversity, but recovery is still possible. A third fire ends up disappearing the forest,” Armenteras says. “In a short time and if no action is taken, most of these ecosystems can be reduced to pastures, savannas, grasslands, and crops.”

According to the study, there was a loss of forest cover in all the studied countries. The highest rates of deterioration, after the occurrence of a single fire in evergreen forests, took place mainly in Panama (64.7%), Paraguay (61.5%) and Brazil (56.6%).

Other countries, such as Mexico, Guatemala and Belize, had a less drastic deterioration in their burned forests (30.7%, 30.4% and 17%, respectively).

Although Bolivian evergreen forests showed high resistance to fires (70.7% persisted after burning), 5.5% of these were later converted to croplands. Next was Brazil, with 3.5% of its forest cover burned and later converted. The study period did not include the particularly severe fires of the past two years in Brazil and Bolivia.

When it comes to deciduous broadleaf forests, which occur in the south of the continent, Chile had the highest rates of transformation, where these burned ecosystems were converted into cropland (26.8%), savanna (22.1 %) and grassland (11.3%). Argentina was next for the highest conversion of deciduous broadleaf forests to croplands, at 17.6%.

In Chile, 19% of burned mixed forests (where primary and secondary forests coexist with crops, for example) became grasslands.

Study co-author Ángela Hernández, from the Center for Research in Ecosystems of Patagonia, attributes the extreme Chilean situation to the fact that since the Augusto Pinochet dictatorship, the government financed and encouraged landowners and companies to plant fast-growing introduced forest species (mainly pine and eucalyptus monocultures) in areas of crops. That decision was established in the mid-1970s under Law Decree 701.

This, Hernández says, led to accelerated land-use change, mainly in the south-central zone of Chile.

“Because it was such a lucrative business, companies began to replace the native forest with fast-growing plantations, which has meant a homogenization of the landscape, now mainly dominated by plantations and generating a large amount of biomass. This meant the beginning of an environmental and socioeconomic problem,” Hernández says.

She says the high population density of the south-central zone means low landscape defenses to mitigate fires, most of which are human-caused.

Climate change and impact on wildlife

Armenteras says the causes of fires should be studied more rigorously “because they increase emissions of gases and particulate matter that affect air quality and contribute to climate change.”

Armenteras explains that three conditions must be met for a fire to occur, which make up the so-called ‘fire triangle’: a fuel, which is the vegetable matter; dry weather conditions and high temperature, and a flame that allows the combustion or ignition.

The first thing that happens when a forest catches fire, Armenteras says, is that the biomass — the “fuel” part of the fire triangle — is consumed. If the forest is in good condition and still retains the humidity of the vegetation, it’s more difficult for the fire to spread. But if the forest is drier because it has been degraded, it will have less humidity and be consumed faster.

The first direct consequence of forest fire is the loss of resistance to future fires. The drying out of the vegetation brings with it changes in the microclimate of the ecosystem. If additional fires occur, they exacerbate the damage, and the forest won’t be able to sequester gases such as carbon dioxide, which has a significant impact on climate change.

Although the study did not consider the impacts of fire on fauna, co-author Tania González, who has studied widely how fires affect small mammals, says these species are affected by burning and the consequent loss of plant mass. She notes that forest fires can affect fauna directly when flames or smoke catch the animals, or indirectly when the vegetation that provides them with habitat, food and shelter deteriorates.

“While large animals, with greater movement capacities, can escape from a fire and later colonize the areas that were affected, the smaller ones with more limited locomotion skills can be hit by the flames or by the loss of the resources they use to survive,” González says.

Fire can also distress competition and predation among species. González says that in Australia, it’s been documented that when forest cover is lost due to fires, the predation pressure on small mammals can increase because there isn’t enough vegetation cover to protect them.

Many flying and non-flying mammals, birds and other species have essential functions in ecosystems such as pollinating and dispersing seeds, González says. “If the fire catches these animal communities, the natural regeneration of plants and the functioning of the ecosystem could be interrupted,” she says.

Armenteras says this study is critical because it reflects that forest fires are not an exclusive problem of the Amazon Basin, which gets most of the media coverage. She says fires are a problem shared by all countries, even when there are differences in how each nation responds to them.

“It is imperative to reduce forest fires,” Armenteras says. “Some solutions could be payments for ecosystem services, condemn environmental crimes, and promote practices for integrated fire management that prevent these environmental disasters.”