Posts Tagged ‘trees and forests’
|Brazil: Amazon deforestation rate plunging
Saturday, September 11th, 2010
In a previous post last week, we discussed a new paper in PNAS showing that new land for agriculture during the ’80s and ’90s came at the expense of tropical forests and savannas.
In this week’s issue of Science, Antonio Regalado reports on satellite imagery (able to record land clearing and fires from slash-and-burn agriculture) showing substantial deforestation declines in the Brazilian Amazon since 2004—from a peak of 27,000 km2/year in 2004 to 7,500 km2/year in 2009.
Why the dramatic downturn over the past half decade?
Environment Minister Izabella Teixeira … credited government enforcement efforts, including cutting off loans to those clearing large amounts of forest for cultivation…
Gilberto Câmara, general director of INPE, said that farmers may now be employing smaller conflagrations to escape detection, and the agency reported a large increase in the number of fires last month. He believes a more accurate survey known as Prodes, due out in November, will show a smaller decline. “We are seeing a process of consolidation in the Amazon, with no new frontiers, fewer large scale cuts, and more small fires to expand existing farms,” he says.
Daniel Nepstad, a senior scientist at the Woods Hole Research Center in Massachusetts, says that recent decisions by large food processors and supermarkets not to buy soybeans and beef from newly deforested areas has helped to slow the rate of deforestation. Some landholders may also be conserving forests in hope of receiving carbon credits.
But Nepstad worries that the picture could change for the worse if prices for
agricultural products, depressed because of a sluggish economy, begin to rebound.
“I think the bigger question is, ‘When the prices come up, will Brazil’s government be
able to hold the line?’ ”
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Photo credit: CIAT
Tags: Amazon, trees and forests
Posted in biodiversity science, food and agriculture, land use | No Comments »
New land for agriculture coming mainly at the expense of tropical ecosystems
Wednesday, September 1st, 2010
There have traditionally been two ways to produce more food for an increasing population: Convert native ecosystems like forests and grasslands to agricultural fields (what we call “extensification”) or make the yields on existing croplands go up, through the use of things like machinery, fertilizers, irrigation, pesticides, and GMOs (what we call “intensification”).
Historically, these processes have occurred in tandem: an initial phase of extensification and land clearing followed by development and intensification. Converting North America’s prairies to corn and wheat in the 19th century is a classic example of the former, whereas 20th-century rise of fossil fuels, and the machines and fertilizer they support, is an example of the latter.
So while it’s not surprising to learn that developing nations in tropical regions are experiencing significant deforestation for food production, as Holly Gibbs and colleagues at Stanford describe in the early edition of the Proceedings of the National Academy of Sciences (citations removed for clarity), it’s important to understand the magnitude of ecosystem change as well as the drivers of change:
This study confirms that rainforests were the primary source for new agricultural land throughout the tropics during the 1980s and 1990s. More than 80% of new agricultural land came from intact and disturbed forests. Although differences occur across the tropical forest belt, the basic pattern is the same: The majority of the land for agricultural and tree plantation expansion comes from forests, woodlands, and savannas, not from previously cleared lands.
Worldwide demand for agricultural products is expected to increase by ∼50% by 2050, and evidence suggests that tropical countries will be called on to meet much of this demand. Consider, for example, that in developed countries the agricultural land area,
including pastures and permanent croplands, decreased by more than 412 million ha (34%) between 1995 and 2007, whereas developing countries saw increases of nearly 400 million ha (17.1%). Moreover, developing countries expanded their permanent croplands by 10.1% during the current decade alone, while permanent cropland areas in developed countries remained generally stable. If the agricultural expansion trends documented here for 1980–2000 persist, we can expect major clearing of intact and disturbed forest to continue and increase across the tropics to help meet swelling demands for food, fodder, and fuel.
Indeed, recent studies confirm that large-scale agro-industrial expansion is the dominant driver of deforestation in this decade, showing that forests fall as commodity markets boom. Rising commodity prices have been implicated in the destruction of Amazonian rainforests for soy production and peat swamp forests for oil palm production in Southeast Asia. Drivers of cropland expansion may impact forests directly through local or regional demand or indirectly through more globalized demand that may occur via market-mediated effects. Although this study does not specifically assess displacement or indirect land use changes, it does highlight the likelihood that intact and degraded forests will be replaced by agricultural land when such changes occur. Regardless of the mechanism, concern continues to mount about the large emissions of carbon dioxide that result when tropical forests are felled and often burned to make room for new agricultural land.
This was more of a land use change analysis, so it didn’t include a lot on the global drivers causing deforestation. It would be a mistake, for instance, to ascribe all of this change to population growth in these tropical regions or efforts to supply more food to people living there. Rather, extensification today is a global phenomenon driven by international trade, as the developing world loses native ecosystems to feed other countries. And destroying forests and peatlands is a major net source of greenhouse gas emissions, so we’re also warming climate as an unintended consequence.
Why not just halt extensification and switch to intensification on existing farmland? It’s expensive—moreso than simply clearing more land in many cases. When the demand for cheap food rules the world, forest clearing in poor countries with abundant, cheap land is often what you get.
It should make us all pause considering that the environmental effects of the demand for goods like soy and palm oil by the industrialized world are being externalized to tropical countries. We are now chopping down tropical forests to make soy burgers, biodiesel, and snack foods. As Cameron Scott notes, “The Amazon, It’s What’s for Dinner.”
Reference:
H. K. Gibbs, A. S. Ruesch, F. Achard, M. K. Clayton, P. Holmgrene, N. Ramankutty, and J. A. Foley (2010). Tropical forests were the primary sources of new agricultural land in the 1980s and 1990s Proceedings of the National Academy of Sciences
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Photo courtesy of leoffreitas
Tags: trees and forests
Posted in biodiversity science, biofuels, food and agriculture, land use, population | 1 Comment »
Can “tree sweating” buffer Europe against future heat waves?
Wednesday, February 24th, 2010
Trees can have a big impact on climate in many ways, as we have been tracking over the past few weeks here at Global Change.
Changes in species ranges, such as the shift of boreal forests northwards into barren-ground tundra, can lower albedo (reflectivity) in winter, thereby warming regional climate.
Last week, we also saw how trees can act as methane chimneys that release this greenhouse gas produced in swampy soils.
In another study, we saw that rising CO2 in the atmosphere can cause forests to grow faster such that they become nutrient starved—especially by soil nitrogen. This causes tree growth to slow. Unfortunately, we saw that most models of climate change (which assume forests are removing CO2 from the atmosphere) don’t take nutrient limitation into account, so scientists are expecting forests to soak up more CO2 than they probably will. This means that atmospheric CO2 rise (and warming) will likely be worse than expected—maybe by as much as 0.5 degree by 2050 and 1 degree by the year 2100.
A further study indicated that increased deciduous forests in the Arctic can increase transpiration (water flow from soils to the atmosphere through plants). This extra water vapor in the atmosphere might act as a greenhouse gas and cause climate in high latitudes to warm by an extra 1 degree C.
In the OnlineFirst issue of Climatic Change (this article is open access), Su-Jong Jeong and colleagues explore other possible forest impacts on climate.1
Specifically, they focused on heat waves in Europe and asked whether forests might be able to help alleviate the impacts of them.
Here’s the idea: In a warmer world with more CO2, forests grow more and there is higher leaf area. This leads to more transpiration. When plant leaves lose water, this acts to cool the plants a lot like sweating does in animals (because the transition of less-energetic liquid water to more-energetic water vapor requires heat input, which comes from the plant). This results in cooler trees and cooler landscapes. Subsequent rainfall from all of this water vapor could supposedly cool landscapes further.
These authors argue that this mechanism can actually cause forested regions in Europe to cool by 1 degree C, thereby potentially lessening the impacts of future heat waves.
Wait a minute, you might be asking, I thought you said that transpiration causes climate to warm? That’s a good point, so let me try to clarify. In the Arctic example above, the researchers were focusing on water vapor as a potential greenhouse gas in the atmosphere. In the Jeong article here, they are focusing on the effects of water evaporation on the temperature of tree leaves at the surface of the earth.
It’s an interesting idea that’s not particularly new. However, there are several potential challenges with the Jeong article that I didn’t see addressed:
- When the water vapor from trees condenses into liquid clouds and rain, this process gives off heat (because we are going from a more energetic gaseous form to a less energetic liquid form). This warms the atmosphere wherever condensation happens, which presumably would also be Europe.
- If increased transpiration is a general feature of European forests in a warmer world, and water vapor remains persistently high in the atmosphere, it can act as a greenhouse gas like the Arctic paper above suggests. This, too, will warm rather than cool climate.
- And, finally, heat waves are often accompanied by droughts when transpiration is generally low because trees are water stressed. This diminishes the cooling effect and can actually cause landscapes to warm as tree leaves warm up and release heat rather than water vapor.
1Jeong, S.J et al (in press) Potential impact of vegetation feedback on European heat waves in a 2 x CO2 climate. Climatic Change
DOI 10.1007/s10584-010-9808-7
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Tags: heat wave, trees and forests
Posted in climate change science | No Comments »
Trees: Another way to increase global methane?
Monday, February 1st, 2010
Methane is a potent greenhouse gas. Unlike CO2, which is produced by the aerobic (in the presence of oxygen) breakdown of organic matter, methane is produced by the breakdown of organic matter in anaerobic environments, such as livestock rumens, wetland soils, landfills, and rice paddies.
When we think of methane production, we don’t usually think about trees, but it looks like they may facilitate methane to the atmosphere. How, you might ask, since most trees live in well-aerated soils?
In a forthcoming article1 in Geophysical Research Letters, Andrew Rice and colleagues show that trees in lowland, swampy areas actually conduct methane produced in soils up their stems and out their leaves, making trees an effective methane chimney.
We’ve known for years that marsh and bog plants do this, but nobody’s really looked at trees before. The trees themselves are not making the methane (that’s done by soil bacteria), but they appear to do two things that increase the overall flux (movement) of methane to the atmosphere: (1) tree stems provide a quick methane escape route from soils to the atmosphere and (2) trees leak root exudates (small organic molecules), which could be an organic carbon source for microbes that make methane.
In this study, they put bags around aboveground tree biomass to catch and measure methane, so it’s clear that #1 happens. However, #2 needs further study. You could measure it by dosing a tree with radiocarbon (14CO2) and then seeing if that gets turned into sugars by photosynthesis and eventually leaked out of roots, ultimately turning into 14C methane (14CH4) that is transported up the tree stems.
How much methane? About 60 teragrams (1012g), or about 10% of the global production each year. Big enough to pay attention to.
1Rice, A.L. et al. (in press) Emissions of anaerobically produced methane by trees. Geophysical Research Letters.
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Tags: trees and forests
Posted in climate change science | 1 Comment »
New ideas about how changing vegetation at high latitudes can cause climate warming to accelerate
Thursday, January 7th, 2010
Most people have probably heard about positive feedbacks at high latitudes and why they matter:
- Warming thaws sea ice, and the decrease in the reflective ice surface causes more solar radiation to be absorbed by the oceans, thereby causing even more warming.
- Warming is causing the northward march of treeline. As boreal conifers in Canada, Alaska, and Siberia migrate into barren tundra, their dark foliage towers above bright snow in winter, causing the landscapes to darken, absorb more sunlight, and warm up, thereby enhancing regional warming.
A new study1 in the Early Edition of the Proceedings of the National Academy of Sciences (open access), indicates that other effects of forest changes might also matter.
Specifically, boreal forests and tundra may become more dominated by deciduous trees (ones that drop their leaves in autumn), which are usually found in warmer regions. What happens if we have a future Arctic dominated by these species?
Using a set of ecosystem and climate models, Abigail Swann and colleagues determined that a rise in deciduous forests would cause an increase in water vapor to the atmosphere (deciduous trees transpire—lose water through their leaves—more than conifers). This makes the atmosphere in the Arctic more laden with water vapor, which is a good greenhouse gas. This warming, in turn, induces further sea ice and snow loss, causing warming to happen more quickly. But wait, there’s more: Warmer, ice-free oceans also release more water vapor to the atmosphere, causing greenhouse warming to increase even more.
How big an effect? About 1 degree C in the Arctic, equivalent to increasing the atmospheric CO2 about 100 ppm in the atmosphere. They found that these changes in water vapor have about the same impact as the changes in reflectivity caused by the color of forest foliage overtopping snow in the tundra.
Things like this are reasons why when warming starts, it can accelerate faster than we think.
1Swann, A. (in press) Changes in Arctic vegetation amplify high-latitude warming through the greenhouse effect. Proceedings of the National Academy of Sciences
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Photo credit: Phil Camill (from my Flickr collection) http://www.flickr.com/photos/pcamill/ / CC BY-NC-ND 2.0
Tags: trees and forests
Posted in biodiversity science, climate change science, polar ice | 1 Comment »
Climate warming worse than previously thought because plants become nutrient starved?
Tuesday, November 24th, 2009
The biosphere—the sum of all living organisms on earth—has tremendous influence on our atmosphere and climate. One active area of research is how the biosphere might respond to rising atmospheric CO2 and temperatures and how this change, in turn, can influence (“feed back on”) climate change.
There are several reasons to believe that the biosphere will generate positive feedbacks on climate (i.e., things that cause warming to accelerate) as a result of warming. For instance, rising temperatures can
- increase soil organic matter decomposition, causing the release of CO2 to the atmosphere, which causes more warming;
- increase permafrost thaw, thereby releasing old carbon and methane bubbles previously locked in a deep freeze;
- cause treeline to advance northwards. As conifer trees move north, the formerly tundra landscapes darken as evergreen trees replace open expanses of snow in the winter. This causes regional climate to warm. In fact, one study1 showed that without its boreal forest tree cover, Canada would be about 5-10 degrees C colder in the winter and spring!
Positive feedbacks are a nightmare scenario because they mean that climate can warm faster than we currently expect, indicating that we have even less time to deal with it. This is part of the reason why scientists are beginning to sound the alarm that CO2 is rising faster than expected and the impacts warming are happening faster than predicted.
There are also reasons to believe that the biosphere will generate negative feedbacks on climate (i.e., things that cause warming to slow) as a result of rising CO2.
- For example, because CO2 is limiting to photosynthesis, rising CO2 is causing plants to grow better. This removes CO2 from the atmosphere and can slow warming.
In a forthcoming article2 in Geophysical Research Letters, Wang and Houlton analyze this negative feedback, and offer some sobering news about it’s ability to slow warming.
Specifically, they argue that most models used in the IPCC assessments do not take into account the fact that nitrogen becomes limiting in soils as plants grow more. Nitrogen is one of the most limiting nutrients to plant growth, which is why it’s often the #1 ingredient in fertilizer used on crops and lawns. Many field studies (example) have shown that trees grown in elevated CO2 experiments eventually stop growing any better than those in ambient air after a few years because soil nitrogen runs out.
Without nitrogen limitation, the IPCC models allow plants to grow more and remove more CO2 from the atmosphere via photosynthesis than they do in reality. This means that forests may not be as strong a carbon sink as we suspect, and we are therefore underestimating the rate of CO2 rise and magnitude of warming—maybe by as much as 0.5 degree by 2050 and 1 degree by the year 2100.
1Bonan, G. et al. (1992) Effects of boreal forest vegetation on global climate. Nature 359:716-718.
2Wang, Y. and B. Houlton (in press). Nitrogen constraints on terrestrial carbon uptake: Implications for the global carbon-climate feedback. Geophysical Research Letters
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Tags: trees and forests
Posted in climate change science | 2 Comments »
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