The dry web effect in the Amazon forest –

Fewer trees – less rain – even fewer trees …: The loss of tree populations in the Amazon region leads to cascading effects that lead to further damage to the forests, the analysis of the model makes clear. Every third tree that dies as a result of drought or deforestation indirectly dies another one. The researchers say regions in the southern part of the Amazon are most affected by the network effect and thus the threat of desertification.

Huge forest area with great biodiversity: The Amazon is not only a fascinating natural wonder, but also plays an important role in the Earth’s climate system due to its carbon sink function. But this lush environment is under threat: in addition to deforestation, climate change causes extremely little rainfall in some regions, causing problems for forests. According to climate forecasts, dry summers such as 2005 and 2010 in the Amazon region may become the new norm from 2050. As part of their research, a team of German and American scientists investigated the extent to which this damage could, in turn, affect the forest.

The forest creates its own rain

As they explain, the forest also provides its own rain by recycling moisture: forest soil and plants absorb a significant amount of rainfall and then release large amounts of water into the atmosphere through evaporation and transpiration. As a result, the forest shapes the weather in the region and generates up to half of the rainfall in the Amazon basin. “Recurring droughts are already leading to measurable changes in the Amazon’s moisture network,” explains co-author Henrique Barbosa of the University of Maryland in Baltimore. “We use these observations to understand and model the consequences of the future climate.” Based on the collected basic information, the researchers developed the so-called a dynamic network model that reflects the complex effects of recycling atmospheric moisture.

As reported by the team, their results show how important the network effect is. Even if only a specific region of the forest is affected by a drought period, the damage goes beyond that region by a factor of 1.3. “More intense droughts threaten parts of the Amazon rainforest to dry out. If the forest cover becomes thinner, this leads to a reduction in the amount of water in the system due to the network effect, and therefore disproportionately greater damage, ‘says first author Nico Wunderling of the Potsdam Institute for Climate Impact Research (PIK). “While we looked specifically at the effects of drought, this principle also applies to deforestation. This means that if you cut one hectare of forest, you actually destroy 1.3 hectares, says the scientist.

critical network effect

However, droughts in the Amazon have very different regional effects, the team points out. “In the Amazon, trees and forest systems are differently adapted to water availability, as some regions have a naturally distinct dry season, while others experience year-round rainfall. We clearly take these local adaptations into account, says co-author Boris Sakschewski from PIK. “Nevertheless, it turns out that even those parts of the Amazon that have adapted to severe dry seasons do not necessarily survive the new climatic normality, and there is a high risk of entire areas becoming savannah or even a completely treeless landscape. The consequences for biodiversity would be catastrophic – as well as for the local, regional and global climate, says Sakschewski.

However, the situation is not hopeless yet, emphasizes co-author Ricarda Winkelmann, an expert in research into elements of subversion at PIK: “Much of the forest is still relatively stable. The network effects of droughts are likely to be limited to some areas in the south-east and south-west of the forest – precisely those where the forest has already suffered severely from deforestation for grazing or man-made soybean. Therefore, we can still do a lot to stabilize the Amazon, ”says Winkelmann. “And we know how to do it: protect rainforests from deforestation and rapidly reduce greenhouse gas emissions, thus limiting further global warming.”

Source: University of Maryland Baltimore County, Potsdam Institute for Climate Impact Research, Article: Proceedings of the National Academy of Sciences, doi: 10.1073 / pnas.2120777119

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