A new study concludes that the oldest and tallest trees resist drought in the Amazon rainforest.
It is known that the Amazon rainforest regulates the global climate system, but in recent years it has suffered droughts that caused the death of its trees. A study published in the journal Nature focused on the sensitivity of photosynthesis, reveals that the oldest and tallest trees are those that have resisted the lack of water.
The US Columbia University team led by Pierre Gentine concluded that trees over 30 meters tall are "three times less sensitive to drought than those shorter than 20 meters."
According to the study, the highest forests in the Amazon are also the oldest, they have more biomass and a more extensive root system, this allows them to reach the deepest moisture retained in the soils during dry seasons.
At the same time, these types of trees are also "more vulnerable" to the dryness of the environment and heat because their leaves have a lower water content, which makes the photosynthesis process more adaptable to the lack of water in the terrain, but more sensitive to fluctuations in water in the atmosphere.
Both heat and dryness are "going to increase substantially with climate change," added Gentine, who noted that the study points out that the response of Amazonian forests to climate variability and drought is not uniform.
He also explained that the research results "suggest that the height and age of forests are an important regulator of photosynthesis in response to droughts."
Rainforests and the global climate system
Tropical rainforests play a fundamental role in regulating the global climate system, as they represent the largest sink for CO2, and the Amazon, in particular, due to its wide geographical extension and its productivity throughout the year, is key to world cycles hydrological and carbon.
The team used remote sensing observations of sun-induced fluorescence (a surrogate for photosynthesis), precipitation, vapor pressure deficit, and foliage height, as well as estimates of forest age and biomass over soil.
Once the data were obtained, they applied statistical techniques to estimate how age and height could modify the sensitivity of forests to droughts.
These results have implications in the capacity of younger forests compared to older ones to resist, or not, future droughts, since deforestation "could increase the fragility" of the forests in the absence of rainfall.
The study “makes it clear that the height and age of a forest have a direct impact on the carbon cycle in the Amazon”, which is “especially significant given the importance of Amazonian forests in the global carbon cycle and climate ”.