by Staff Writers
Washington DC (SPX) Feb 29, 2016
Sometimes you can't see the forest for the trees. In the Amazon, the opposite is true: without truly seeing the trees, you can't "see" the forest and understand the seasonal patterns of photosynthesis that play a major role in ecosystem and climate models, according to new research funded by the National Science Foundation (NSF).
"We can't understand the forest unless we understand the individual details," said Scott Saleska, associate professor of ecology and evolutionary biology at the University of Arizona. Saleska is part of the research team that uncovered the Amazon forest seasonality. The research was published in the journal Science.
The work was supported, in part, by NSF's Partnerships in International Research and Education (PIRE) program, which helps catalyze strong international engagement by the U.S. science and engineering community. Projects generate new knowledge and discoveries; promote a diverse, globally engaged U.S. workforce; and build the institutional capacity of U.S. institutions to engage in productive international collaborations.
Saleska was the lead principal investigator on the Amazon PIRE, which focused on how Amazon forests respond to changes in climate, such as fluxes of water, carbon dioxide and energy.
Saleska discussed the work he and his collaborators - including a group of students and postdocs funded through the PIRE - did in the Amazon, and why it matters. Learn more about the discovery here.
What questions were you trying to answer with this research?
Some seasonality is from climate; there's a dry season and wet season - in the dry seasons there's more sunlight, in the wet season there's more water. We wanted to know whether there was additional seasonality in the biology of the trees, or leaves themselves, that explained the behavior of the forest. That's the big picture question.
But the research also solved a seeming discrepancy between ground and space observations.
Ground-based observations show pretty dramatic, strong seasonal patterns in forest photosynthesis. But from space there's observations from satellites which show much more subtle seasonality. So one question is: Why the difference - and can we explain it? What we've been able to do, by using cameras, is look at the intermediate scale. The cameras looked at individual tree crowns, underneath the scale that the satellites are able to see. We found a pattern that is both consistent with the satellite data, and a change in leaf age that explains the seasonality in the flux. Both are right.
What did you find?
Here, they're doing all this in the space of a month. So a lot of trees lose leaves and grow them at the same time, and this happens much more prevalently in the dry season - when photosynthesis is also increasing. But this is seasonal, and photosynthesis drops back down in the rainy season.
Where were the cameras? How did they work?
Why is this research important?
If we're not able to understand the mechanism of how those trees respond to those changes in climate ever year, then we have some problems. It's sort of like a first-cut test of our models for predicting the response of trees to climate. Do they work? Do they work at the annual time scale? If they don't work at the annual time scale, why should they work at any other scale?
So it adds a new layer of sophistication into climate models. But what about our understanding of the forest itself, and how it interacts with the climate?
This might be an important biological adaptation that sustains the forest through dry periods. This relates to the question of how robust or sustainable the forest is in general. The specific thing we see - the synchronization of leaf growth and death - allows individual trees to grow more in the dry season, the time when they might otherwise be limited by drier conditions. But this individual behavior has whole-system consequences.
Trees transpire more water when they grow more: they moisten the atmosphere, which is quite dry during the dry season. If all, or most, of the trees do this, they moisten the atmosphere a lot, which atmospheric scientists have found stimulates the return of the wet season sooner than it would otherwise come back.
These two mechanisms - the boost in capacity of individual trees, and the changing of the environment they're in - both sustain the forest at an individual level and a whole-system level. So understanding that is very important for understanding how climate change in going to happen. And how trees and vegetation in general can actually affect the climate itself.
National Science Foundation
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