Tuesday, July 11, 2006

Stepping Back To Get A Clearer Picture

Sometimes things just aren't how you think they are, and it takes extraordinary measures to find out what's what. Sometimes getting the whole picture can take seeing things from a distance, and in the case of the enormous Amazon rain forest, this can even necessitate getting off the planet. Satellite images are providing surprising new information as scientists try to understand the climate's effect on the rain forest, and the forest's effect on the climate. In a lengthy, but interesting, article from NASA's Earth Observatory, Rebecca Lindsey examines surprises that have been forthcoming from the study of images of Amazonia, taken over the last two decades, in the process of mapping Earth's vegetation patterns. The article focuses on University of Arizona remote-sensing ecologist Alfredo Huete, the data processing and mapping techniques he and his team developed for NASA, and the unexpected turn their view of the rain forest took after data began to be accumulated and analysed.

Lindsey spends a good deal of time looking at how Huete developed his techniques for mapping vegetation, and the hoops he jumped through to ensure the model's accuracy at capturing changes in the Earth's vegetation throughout the year. As testing went along "...the maps matched real-world seasonal changes in vegetation in different ecosystems, from African savannas to eastern North American forests." As the program developed, Huete became more and more confident of his methods, but there was one consistent problem; the Amazon didn't seem to be behaving properly. Images seemed to indicate that the rain forest actually gets greener during the dry season, which, as anyone who has spent time watering their lawn in the summer can tell you, makes no sense. Huete did a great deal of tweaking to try and locate the source of the problem, but kept coming back to the same result, and observations on the ground confirmed the conclusion. The Amazon does indeed experience its growing season when the rains stop falling. The bad season in the Amazon is the time of year when the rest of the Earth's fields and forests come to life, when life-giving water penetrates the soil and reaches thirsty roots.

So, how to explain the anomaly? You have to get pretty far into Lindsey's article to get to the reasons why it does, in fact, make sense for the Amazon to follow a separate growing pattern than the rest of the world. Fortunately, if you are time-challenged, I have done the necessary reading for you. There are three factors that affect plant growth: precipitation, sunlight and temperature. The key to Amazon vegetation growth is the sunlight factor. During the rainy season, there is increased cloud-cover, limiting light, and thus growth. The dry months provide the added light that the forest needs, and the growing commences. In fact, the longer the dry season, the more the rain forest greens up. Odd, huh? The secret lies in the giant Amazon trees. According to Lindsey, they have root systems that go down up to sixty feet into the soil, so they retain access to the rainy season's water during the dry season's burst of sunlight. Thus they have the perfect combination to help them stretch a little farther up into the heavens. This holds true for the undisturbed forest lands, but for the harvested lands it's not the same story:

...the dry-season green-up only happens in undisturbed forests, stresses Huete. At locations where the forest has been converted to pasture or farmland, the dry season has the more intuitive effect: the vegetation “browns down” in response to decreased soil moisture. Once the deep roots of the mature trees are lost, the access to the water stored deep in the soil is lost as well.
So different rules apply to the undisturbed rain forest than apply to any other area of land. It is unique in how it functions in the world.

This changes the way scientists must look at the rain forest and climate change. The Amazon is so huge, it can't help but affect the balance of carbon dioxide in the air. Most models that don't take the reversed seasonal shift of forest growth into account see ecosystem collapse in the future if global warming, affected by airborne carbon, causes the region to dry, and predict that eventually the area could become a savanna. The new model, however, where the forest thrives during the dry season, calls those conclusions into question, not refuting them, but clearing indicating the need for further study before proclaiming the forest's imminent demise. Ecologist Scott Saleska was a part of a research group which designed and operated instruments "... as part of NASA’s contribution to a Brazilian-led international research project called “LBA,” short for the “Large-Scale Biosphere-Atmosphere Experiment in Amazonia.” His research helped Huete draw his conclusions. Saleksa says the new information means they have to reexamine the old models:
“But if these models are getting the seasonality wrong, then the impacts [of climate change] may not be what we expect,” he continues. Predictions of ecosystem collapse are based on the idea that the dry season is a time of stress and declining greenness. If that isn’t true, then perhaps the Amazon will be more resilient than the models predict. On the other hand, a typical dry season isn’t the same as a lengthy El Niño-induced drought. Previous studies, including a drought-simulation experiment conducted during LBA, indicate that the more severe, extended declines in rainfall that can happen during strong El Niño events do produce stress in the forest, especially fragmented or damaged areas. With forest disturbance on the rise and predictions by some climate models that El Niño events may increase as climate warms, the fate of the Amazon is unclear.
So, the forest may be more resilient than previously feared. That's good. It's hopeful, anyway, and I always like hopeful. Of course, as Saleska indicates, the jury's still out about how climate change will affect the Amazon rain forest, and how with its treasure trove of carbon, the forest will affect the climate. Long-term drought may still cause as much damage as it's been feared it would. Further study is needed. Fortunately, further study is planned. Saleska and Huete will soon be collaborating to analyse the data gathered thus far, and "...come up with a basin-wide estimate for the flux of carbon in the Amazon." Hopefully this will provide a reliable gauge for comparing future ecosystem changes. So now we need a good long dry spell to test some theories:
In the meantime, says Saleska, everyone is keeping their eyes out for the next strong El Nino because observations collected during the event could provide the next key piece of the puzzle of how the Amazon responds to large-scale climate variation and change. Knowing the Amazon’s baseline seasonal response should help scientists judge when and how future climate events may disturb the balance of such an important and sensitive ecosystem.
It'll be interesting to see whether this information is picked up by any of those who are especially worried about climate change. I'm not hopeful on that front. The data gathered by Huete and Saleska doesn't necessarily contradict their point of view, but it doesn't support it either, so chances are it will go unnoticed. You never know, though, people can sometimes surprise you. Of course, global warming advocates (I mean advocates for the position, not the event. I'm pretty sure the latter don't exist) may see reasons why this information makes things appear much worse rather than better. I don't know. I just know I'll keep watching the process as the experts collect and sort the data. I'm glad we have the ability to see thing from a distance, to step out into space, so that we can get information that was unavailable to us just a few short decades ago. Now we just have to figure out what it all means.