Published in Nature: The arrival of the dry season in the Amazon is the rainforest’s cue to go green, according to a study by UTS researchers Dr Natalia Restrepo-Coupe, Professor Alfredo Huete and international collaborators.
According to the authors, both satellite remote sensing and ground-based observations support the conclusion that Amazon forests green up with sunlight in the dry season.
By contrast to dry areas, where new leaves come out with the onset of rain, in the tropical rainforest growth is limited by sunlight, the study found.
Professor Huete says that in the tropical rainforest everything is living in water because it’s nearly always raining.
"What trees need more than anything else is sunlight.”
However, this contradicts a previous study from other scientists, also published in Nature, which suggested that water is the limiting factor rather than sunlight. According to this 2014 study rainforest activity is constant throughout the year, neither excited nor depressed by extended sunlight - a conclusion solely based on satellite observations.
By contrast, the UTS researchers and their coworkers reached their conclusion by connecting data obtained from an 80-metre tower above the Amazon forest canopy – including a direct measurement of carbon and oxygen exchange as well as leaf data – with data from the NASA MODIS sensor.
The interest in this field of research is understandable: massive-scale biomes and ecosystems are behaving in a way that is contrary to what you might expect.
But Professor Huete believes that the team's finding does make sense, as the gigantic tree forest systems establish very deep roots - 20 metres and deeper underground - with an unlimited water supply because even in the dry season it rains every day.
And referring to the 2014 challenge, he makes the point that as a basic principle scientists should never rely on satellite data alone.