Fewer trees – less rain – even fewer trees…: Losses of the tree population in the Amazon region lead to cascading effects that lead to further forest damage, a model analysis makes clear. For every third tree that is lost due to drought or deforestation, another one dies indirectly. The researchers say that the regions on the southern edges of the Amazon region are most affected by the network effect and thus by the threat of desertification.
Huge forest areas with enormous biodiversity: The Amazon region is not only a fascinating natural wonder, it also plays an important role in the earth’s climate system due to its function as a carbon sink. But this lush habitat is under threat: in addition to deforestation, climate change is causing unusually little rainfall in some regions, which is causing problems for the forest. According to climate forecasts, dry years like 2005 and 2010 in the Amazon region could become the new normal from 2050 onwards. As part of their study, the team of German and US scientists has now investigated the extent to which this damage can in turn affect the forest.
Forest makes its own rain
As they explain, the forest also provides its own rain through moisture recycling: forest soil and plants absorb a significant part of the precipitation 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 precipitation in the Amazon basin. “Recurrent periods of drought are already leading to quantifiable 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 a future climate.” Based on the basic information collected, the researchers developed a so-called dynamic network model, which reflects the complex effects of atmospheric moisture recycling.
As the team reports, their results demonstrate the significant importance of the network effect. Even if a dry period only affects a certain region of the forest, the damage extends beyond this region by a factor of 1.3. “More intense droughts threaten to dry out parts of the Amazon rainforest. If the forest cover becomes thinner, this leads to less water in the system overall due to the network effect and thus to disproportionately more damage,” says first author Nico Wunderling from the Potsdam Institute for Climate Impact Research (PIK). “While we looked specifically at the effects of drought, this rule also applies to deforestation. This means that if you cut down one hectare of forest, you actually destroy 1.3 hectares,” says the researcher.
critical network effect
However, as the team emphasizes, the droughts in the Amazon region have very different regional effects. “In the Amazon, trees and forest systems are differently adapted to water availability, as some regions have a naturally pronounced dry season while others experience year-round rainfall. We expressly take these local adaptations into account,” says co-author Boris Sakschewski from PIK. “Nevertheless, we are finding that even those parts of the Amazon that have adapted to strong dry seasons will not necessarily survive a new climate normality and there is a high risk that entire areas will turn into savannah or even completely treeless landscape. The consequences for biodiversity would be catastrophic – as would those for the local, regional and global climate,” says Sakschewski.
However, the situation is not yet hopeless, emphasizes co-author Ricarda Winkelmann, an expert in tipping element research at PIK: “A large part of the forest is still relatively stable. The network effects of droughts are likely to be limited to certain areas in the south-east and south-west of the forest – and these are precisely those areas where the forest has already suffered severely from human clearing of forest for grazing or soybeans. So we can still do a lot to stabilize the Amazon,” says Winkelmann. “And we know how to do that: protect the rainforest from deforestation and rapidly reduce greenhouse gas emissions, thereby 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