Amazon plants trigger seasonal change
Photo: Kevin Day
The Amazon rain forest has two seasons: dry and wet. Scientists believe the trees themselves influence the transition between seasons, and the amount of rainfall.
That’s according Ranga Myneni of Boston University. He uses satellites to look down from above at trees that look green and lush all year round. Satellites measure radiant light reflected by green leaves. They reveal more or less dense leaf cover. Myneni told Earth & Sky that, contrary to what you might expect, there are 25% more leaves in the dry season.
He said that’s because there’s a lot of water deep underground, even in the dry season. The trees have evolved an extensive root system to tap into this water. Meanwhile, during the rainy season, there’s less sunlight and less leaf production.
Ranga Myneni: In the rainy season the sky is cloudy and there is less light. And in the dry season the skies are generally less cloudy, and there is more light. And therefore, given that there is water, these trees are limited by light, so in the dry season they tend to put more leaves.
During this greener dry season, the leaves themselves pump more water into the atmosphere, which helps trigger the gradual change from a dry to a wet season.
Our thanks today to NASA: explore, discover, understand.
Myneni said that measuring leaf coverage in the Amazon is important for several reasons. For example, he said, it’s likely that leaves store carbon emitted by industrial activity that otherwise would remain in the atmosphere and contribute to global warming. Knowing more about when rain forest trees are at their leafiest could help scientists understand the role of rain forests in helping to limit this greenhouse gas.
Our thanks to:
Ranga Myneni
Additional Teacher Resources
Exploring the Environment Module: Tropical Poison
In this module for grades 9-12, students analyze a case study and make recommendations concerning competing uses for rainforest resources.
NASA: Earth Observatory – The Amazon’s Seasonal Secret
This article discusses research being conducted to help discover what causes the length and timing of the rainy season in South America to change from year to year.
NASA: Earth Observatory – Defying Dry: Amazon Greener in Dry Season than Wet
This article discusses the question: How can the rainforest thrive during times of seasonal drought?
