Intact forests crucial to Amazon ecosystem resilience, stable climate

Three recent South American studies emphasize the importance of intact forests to healthy habitat and a stable climate — both locally, and at a great distance.

Article by Claire Salisbury.

Three new South American studies have shown how important intact, healthy forests are for both the resilience of local ecosystems, and for local climate stability, and even for the healthy growth of forests hundreds of miles away.

Caatinga after the rain. The Caatinga is a dry forest habitat found in Brazil’s northeast. Adapted to periodic droughts, the vegetation responds to the return of rain. A new study shows that the resilience of Caatinga forest to drought is strongly influenced by its condition and protected status. Photo by A. Duarte on flickr used under a CC BY-SA 2.0 license

The new research helps illuminate the myriad interwoven connections between trees and their environment: forests help create local microclimates, generate rainfall, and even influence global carbon and oxygen levels. Deforestation can alter and degrade the surrounding environment.

Enhancing dry forest drought resilience

The first study, published in Biotropica, focused on a unique habitat found in northeast Brazil. The Caatinga dry forest is a semi-arid habitat characterized by thorny trees and shrubs, and succulents such as cacti, which are adapted to periodic droughts. Historically, when rains return after drought, the vegetation bounces back.

But scientists are concerned that the Caatinga forest is becoming vulnerable to the increasingly intense droughts in the region, and reaching the limits of recovery. Extreme droughts are forecast to become more common due to climate change, so the long-term survival of the Caatinga will depend on the ecosystem’s response to changing conditions.

To investigate Caatinga drought resilience — that is, how quickly the forest can respond to water availability once a drought ends — scientists from Brazilian and Bolivian institutions used satellite images coupled with data from weather stations to analyze how the condition of the Caatinga vegetation has changed through time. Specifically, they looked at the differences in vegetation productivity (a measure of plant growth) in response to drought and rainfall between areas that had, or had not, been previously deforested, and areas under strict protection, or that were designated for sustainable use.

Indigo macaws (Anodorhynchus leari), an endangered species endemic to the Caatinga. Degraded and unprotected Caatinga forest was less resilient to drought than intact forest and strictly protected areas. Scientists argue that stronger protection is needed for the conservation of the biome. Photo by Joao Quental on flickr, used under a CC BY 2.0 license

They found that vegetation productivity always increased in response to rainfall, but the way it did so was strongly influenced by its protected status and condition.

Once water availability increased, areas that had been previously deforested were less productive than intact areas. Similarly, productivity in strictly protected areas recovered more quickly than in sustainable use or unprotected areas. What’s more, strictly protected areas had higher productivity even during the worst drought.

What this shows, the scientists say, is that forest integrity is crucial for habitat stability and resilience. Degradation makes it harder for the Caatinga to recover from climate fluctuations. Strictly enforced protected areas not only safeguard the biodiversity within them, but also act as buffers against the impacts of climate change on the whole ecosystem.

The Caatinga biome is home to many endemic and threatened species: for example, thirty percent of the region’s 1,200 plant species are found nowhere else. The endemic indigo macaw (Anodorhynchus leari) is classified as Endangered by the IUCN, and the three-banded armadillo (Tolypeutes tricinctus), which is found primarily in Caatinga habitat, is classified as Vulnerable. Despite its importance to biodiversity, only a small fraction of the Caatinga currently lies within protected areas, and it is highly threatened by habitat loss and fragmentation.

Increasing the conserved area network, and defending existing reserves against the trend of downgrading protection status that has been widespread across Brazil under the Rousseff and Temer administrations, could help reduce the risks facing the Caatinga, the researchers say. Without stronger protection, the Caatinga could be lost to intensifying drought and desertification.

Amazon rainforest and cattle pasture. Deforestation and land use change extending south from the Amazon’s southern limits influences local and distant climate, a recent study shows. Photo by Rhett A. Butler / Mongabay

Identifying long-distance climate / forest connections

A second study found that habitat degradation doesn’t just matter locally, but has remote impacts. The research, encompassing the whole of South America, showed that changes in land cover not only directly impacts the local climate, but also affects the climate and vegetation dynamics in distant, undisturbed forest.

The study, published in Environmental Research Letters, used computer simulations to explore the impact that changes in land use and land cover can have on both climate and productivity. The research team, led by scientists from the University of Lund, Sweden, focused on the implications of intense land use change in two areas — the region extending south from the Amazon rainforest’s arc of deforestation in central Brazil, and northern Argentina’s temperate grasslands — both locally, and across the Amazon basin.

For the simulations, the scientists used a model that included a variety of data, relating to vegetation types, soil moisture levels, and the atmosphere above and below the canopy. Climatic and vegetation data was coupled so that changes in one had an effect on the other.

To measure the impact of land cover and land use change, the team, led by Minchao Wu, ran simulations for the time period 1996-2005 with and without the data on land cover change. This effectively showed how the climate and vegetation would look if the land was still in a more natural state, as compared with how it looks as a result of deforestation and degradation of local habitats.

The effects Wu’s team observed in their simulations differed between regions, and between wet and dry seasons. Overall, land use change resulted in the dry season being warmer across the whole continent, and this was most pronounced in the southern Amazon which was as much as 2.2 degrees Celsius hotter than if land cover change had not taken place.

But the most surprising impact, Wu said, was seen 500 kilometers (310 miles) away from where land use change had occurred: Amazonian plant productivity changed as a direct result of the deforestation occurring far to the south.

What’s more, there was a contrast in the forest’s response: the northern Amazon increased in productivity during the dry season, while the southern Amazon’s productivity decreased. In both cases the change was by as much as 10 percent.

A storm over an agricultural landscape in the Brazilian Amazon. The Amazon generates about half of its own rainfall, and deforestation affects the way water is recycled into the atmosphere. The three studies presented in this article suggest that climate change will intensify the impacts of deforestation locally, across the Amazon basin, and even across the South American continent. Photo by Rhett A. Butler / Mongabay

Land use change, say the scientists, causes a suite of interrelated changes to the links between earth and air. Open, unforested, land is warmer than land shaded by a forest canopy, creating a temperature gradient both vertically, from soil to sky, and horizontally, between open and forested areas. Temperature gradients lead to convection currents, and this, coupled with shifts in the rate of evapotranspiration — the movement of moisture from soil, through plants, into the atmosphere — influences the extent and location of cloud cover.

The reason for the contrasting changes in productivity? Cloud cover, or lack of it, affects the amount of sunlight reaching the canopy, and alters how much photosynthesis takes place.

Changes to cloud distribution as a result of warming have been predicted in similar studies said Jaya Khanna, an atmospheric scientist at the University of Texas at Austin who was not involved in this research. Where Wu’s study goes a step further, Khanna said, is in showing how this can lead to reduced productivity in southern Amazonia, an area “already identified as a region at climate change risk.” Still up for debate is the fate of the more pristine northern Amazon, she said, “as this region is not water limited nor susceptible to land-use-induced warming. So the impacts of a small increase in [productivity] in this wet region due to remote effects of land-use need more investigation.”

The implications of changes in productivity are potentially far-reaching, explained Wu. “[Productivity] changes can link to the ecosystem’s ability to absorb atmospheric carbon,” he said. By altering food availability for Amazonian herbivores, it might also influence “the food web of the ecosystem.”

How deforestation could impact future rainfall patterns

A third study, published in Geophysical Research Letters, focused on the links between the water cycle and deforestation occurring within the Amazon basin.

This research, led by Clara Zemp, of the University of Göttingen, Germany, looked at where water was entering the atmosphere via evapotranspiration, and where it was being returned to the forest as rainfall. As in Wu’s study, the southern Amazon was found to be particularly vulnerable to the effects of distant deforestation.

Moisture evaporating from the Amazon canopy. Land use change outside of the Amazon region affects cloud cover over untouched Amazon forest hundreds of miles away, which results in increases and decreases in plant productivity. Photo by Charles Peterson on flickr, used under a CC BY-NC 2.0 license

Zemp used a combination of satellite images and simulations reflecting various future Amazonian deforestation scenarios in order to analyze how future rainfall patterns might play out, and what effect this could have on the resilience of forest ecosystems.

However, Zemp’s methods — in order to isolate the role of evapotranspiration itself — didn’t account for the other influential factors arising from deforestation, such as the changes to atmospheric circulation patterns that Wu focused on. Even so, Zemp still found that dry-season rainfall could decrease by 2 to 8 percent across the Amazon basin as a whole, and by up to 20 percent locally, by 2050. This was under a business as usual deforestation scenario, with the precise outcome depending on the calibration of the model.

The worst hit regions, according to this study, will be the Amazon’s southwest — including parts of the Peruvian and Bolivian Amazon, and the Brazilian states of Rondônia and Mato Grosso — and the La Plata basin which drains portions of northern Argentina, Uruguay, Paraguay, Bolivia and Brazil. For the Amazon’s southwest — about 25 percent of the entire basin — deforestation occurring anywhere in the region is especially bad news.

“I was surprised to see that, regardless of which part of Amazonia is deforested, it is always the same [southwest] region, that suffers most in terms of ecological impacts,” Zemp said. “This was totally unexpected.”

Two things could explain this area’s vulnerability, Zemp explained: “One, this region is under great climatic influence from the rest of the Amazon forest, as a large proportion of its rainfall originates from transpiration of the trees located in the entire Amazon basin. Two, this region is already nowadays very vulnerable to drought due to its relatively long dry season. Hence a small rainfall reduction due to deforestation has drastic ecological impacts.”

Illegal logging operation in the Amazon. The three studies show the subtle but very powerful influence of land use change on forest resiliency and climate change at the local level, regionally, and across the South American continent. The findings come at a time when Brazil is reducing environmental protections and moving forward with plans for cattle, soy and other large-scale agricultural expansion, mining, and the building of newly proposed dams, roads, railways, and industrial waterways, which could seriously impact the Amazon rainforest. Photo by Sue Branford for Mongabay

Stronger impacts with climate change

What might these long-distance ecological and climate connections mean in the long-term, as global temperatures, drought intensity, and CO2 levels increase in coming years? Both Wu and Zemp agree that these escalating influences will result in deforestation impacts becoming more pronounced.

But exactly how this plays out across the Amazon and South America depends on where future land use change takes place, whether the Atlantic trade winds change in strength, and the precise nature of future dry seasons, explained Wu. “Extreme drought or prolonged dry seasons over the deforested area would enhance the thermal contrast over the Amazonian areas, and it might thus strengthen the teleconnection.”

Although these three studies vary in their scope, predictions and conclusions, they all share an overarching message: intact forests are needed for healthy, resilient ecosystems near and far, particularly as climate change and extreme drought intensify.

“The regions that we identify as hot-spots, where deforestation would have the strongest ecological impact on the Amazon forest, coincide with regions likely to be degraded or clear-cut in the near future, according to recent predictions,” concluded Zemp.

“This means that it is urgent to reduce deforestation and forest degradation in order to avoid dramatic ecological consequences on the entire Amazon forest, and in particular on the southwestern part that already showed difficult recovery after recent extreme droughts.”

Citations:

Acosta Salvatierra, L. H., Ladle, R. J., Barbosa, H., Correia, R. A., and Malhado, A. C. M. (2017) Protected areas buffer the Brazilian semi-arid biome from climate change. Biotropica doi:10.1111/btp.12459

Wu, M., Schurgers, G., Ahlström, A., Rummukainen, M., Miller, P. A., and May, W. (2017) Impacts of land use on climate and ecosystem productivity over the Amazon and the South American continent. Environ. Res. Lett. 12: 054016

Zemp, D. C., Schleussner, C.-F., Barbosa, H. M. J., and Rammig, A. (2017) Deforestation effects on Amazon forest resilience. Geophysical Research Letters 44: doi:10.1002/2017GL072955

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