This is What Happens to Rainforests When There’s Not Enough Rain

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A decline in rainfall caused by climate change could endanger the planet’s rainforests by reducing soil moisture that’s essential to maintaining their biodiversity and resilience, according to a new study published in Nature.

Rainforests help to cool the Earth by absorbing planet-warming carbon dioxide and producing oxygen, but both the extent of tree cover and the diversity of plant and animal life they can sustain is falling due to deforestation.

The study led by researchers from the University of Haifa in Israel and the Smithsonian Tropical Research Institute in Panama compared soil humidity and precipitation data with the survival of saplings and the diversity of trees in the rainforest of central Panama.

It found that in dry years, diversity fell by about 15% and in wet years it increased by about 15% because insects and fungi — which play a vital role in preventing any tree species from becoming dominant — thrive in more humid soil.

“We have identified a different way in which climate change and anthropogenic disturbances affecting water availability can affect forests,” Edwin Lebrija-Trejos, an author of the study, said in a statement. “The more dry years or conditions we experience, the greater the threat of damage — not only to species diversity in rainforests but also to the contribution these forests make to humanity.”

Some rainforests are already close to tipping points due to challenges including a lack of water. Experts at the United Nations Environment Programme have warned that a “cascade” of destabilizing impacts could follow the demise of ecosystems that play a central role in regulating our planet’s atmosphere.

Diversity is key to rainforest resilience, allowing one species to step in for another to perform the photosynthesis necessary to produce oxygen, the researchers said.

“You can think of it in terms of a factory where only one person knows how to perform a certain task in the production chain, compared to a factory where various workers can all perform several tasks,” Lebrija-Trejos said. “In the former case, as soon as that worker goes on sick leave, the whole process is stuck. In the latter, others will be able to step in.”