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The Worldwide Vulnerability of Forests

Science & Tech  (tags: forests, ecosystems, environment, endangered, conservation, climate-change, climatechange, water, research, science, protection, nature, habitatdestruction, globalwarming, globalwarming, world, climate, discovery, investigation, scientists )

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One of the great scientific tasks of the day is to understand how and why trees die. It may seem like a question that would have been answered many decades ago, but it was not --at least not at a detailed physiological level. Now, amid growing signs world

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JL A. (275)
Monday November 26, 2012, 11:08 am
Green - Energy, the Environment and the Bottom Line
November 23, 2012, 8:26 am
The Worldwide Vulnerability of Forests

One of the great scientific tasks of the day is to understand how and why trees die. It may seem like a question that would have been answered many decades ago, but it was not - at least not at a detailed physiological level. Now, amid growing signs worldwide that forests are at risk as the climate changes, scientists are trying to catch up to events.

Lately, more and more evidence is pointing toward a mechanism known as hydraulic failure as the culprit in many large-scale forest die-backs. This occurs when drought reduces the flow of water into tree roots. The trees take measures to limit the loss of water through their leaves, but trees need water flowing through them as much as humans need blood. Eventually, if the drought is bad enough, the tiny tubes that carry water up the trunk of the plant can fill with air bubbles.

Detailed understanding of this mechanism may still be developing, but anybody who has forgotten to water a house plant has seen the consequences. The flow of water through the body of the plant is interrupted, and unless moisture is restored to the soil, it can droop and eventually die.

Now comes a surprising new paper from an international research team presenting ominous findings about the risks to forests from global warming and its accompanying water stress.

For the study, released online on Thursday by the journal Nature, Brendan Choat of the University of Western Sydney in Australia, Steven Jansen of Ulm University in Germany, and a large group of their colleagues compiled data from 226 forest species at 81 sites worldwide. They found that around 70 percent of the species operate with only a narrow margin of safety when it comes to their water supply. In other words, many of the world's important forest species are vulnerable to hydraulic failure.

In effect, the trees have adopted an aggressive evolutionary strategy, creating robust water-moving machinery that allows them to grow quickly and out-compete other trees during times of adequate rainfall, but putting them at risk of dying when water is scarce.

That means that virtually all types of forests, even in regions that seem to get plenty of rain today, are vulnerable to increased drought and increased evaporation driven by higher temperatures. If the changes in rainfall and soil moisture in coming decades turn out to be as big as many scientists fear, the Choat-Jansen paper implies that the result could be massive die-backs, shifts in the composition of forests, and a transition from forest to grassland in many regions.

That may sound alarmist, but a developing body of evidence suggests that it is already starting to happen. Last year, for example, I wrote about the large forest die-backs that are being seen in the American West and the Pacific Northwest because of mountain pine beetles, an insect pest that is moving farther north because of global warming.

We are also seeing huge impacts on forests from water stress in the Mediterranean, the Amazon and many other regions.

William R.L. Anderegg, a Stanford University researcher who was uninvolved in the new paper but is doing related work, told me he saw the new research as "a major step forward" in gaining a more complete global understanding of the risks to forests from climate change.

The new paper "tells us that many, many tree species live close to the dry edge of what they can tolerate, even if they live in a very wet area," Mr. Anderegg said in an e-mail. It makes evolutionary sense, he added, because "no matter your environment as a tree, you would want to maximize your growth in order to compete with other trees, while still narrowly avoiding death from water stress. The practical and critical outcome of this is that trees and forests, globally, appear to all be relatively vulnerable to drought-induced mortality."

Climate change puts at risk not only the rich diversity of life in the world's forests, but also the ability of those forests to suck carbon dioxide out of the air, as they do today in immense volume, helping to limit global warming. In other words, if forests start dying from global warming, that means the warming will get worse, presumably killing more forests - a dangerous feedback loop.

"The consequences of longer droughts and higher temperatures are potentially dramatic," Dr. Choat, Dr. Jansen and their colleagues wrote in the new paper. "For example, rapid forest collapse as a result of drought could convert the world's tropical forests from a net carbon sink into a large carbon source during this century."

The big question now is how much ability the world's trees have to adapt. In theory, one might imagine that young trees growing under drought stress would shift their architecture in ways that would limit their risk. But whether they really have the genetic capacity to do this, or to do it quickly enough to keep up with the rapid climatic shifts projected for coming decades, is an open issue.

A distinct possibility, the scientists wrote, is that "the rapid pace of climate change may outstrip the capacity of populations to adapt."

In a commentary accompanying the paper, Bettina M.J. Engelbrecht of the University of Bayreuth in Germany, who was not involved in the research, writes that the accumulating scientific evidence sounds "a warning bell that we can expect to see forest diebacks become more widespread, more frequent and more severe - and that no forests are immune."


Kit B. (276)
Monday November 26, 2012, 11:31 am

For some years now we have witnessed new destructive beetles, forests being choked by lack of normal water cycles that feed deep under ground water reserves. I don't think it's trite to say that "trees are the lungs of the earth", we may be playing catch up on how to protect our trees, but we need to learn fast. Very interesting and informative article, thank you J L.

JL A. (275)
Monday November 26, 2012, 11:44 am
Kit, thank you for reminding me of the report on our ground water depletion that was posted earlier this month--that probably is a factor in this issue as well. You are welcome.

Michael Kirkby (85)
Monday November 26, 2012, 2:12 pm
Noted & posted

JL A. (275)
Monday November 26, 2012, 2:26 pm
Thanks for sharing. You cannot currently send a star to Michael because you have done so within the last week.

Terry V. (30)
Monday November 26, 2012, 5:37 pm

JL A. (275)
Monday November 26, 2012, 5:39 pm
You are welcome Terry

Julie P. (149)
Monday November 26, 2012, 7:08 pm
"Modern day concentrations of ground level ozone pollution are decreasing the growth of trees in the northern and temperate mid-latitudes, as shown in a paper publishing December 9 in Global Change Biology. Tree growth, measured in biomass, is already 7% less than the late 1800s, and this is set to increase to a 17% reduction by the end of the century."

"Influence of ozone and nitrogen deposition on bark beetle activity under drought conditions"

Study demonstrating (under drought conditions) elevated ozone levels and nitrogen pollution contributes to increased tree mortality and bark beetle activity.;jsessionid=Jp49pqsXV9MY0dRNqwqa.10

The stressors facing trees are explained very well in a blog on the Forest Ecology Network. It indicates that the coastal fog in Maine can be 10 times more acidic than the rain.

" To give some idea of what the trees are dealing with, German researchers have detected some 400 synthetic organic compounds in a single cubic meter sample of air! In actuality, our rain and fog have become a toxic stew, with the pollutants acting synergistically on our trees in ways we are still far from fully understanding."

Article date: March 1998.

How long before the world collectively wakes up?


JL A. (275)
Monday November 26, 2012, 7:18 pm
Wow Julie! Such a wealth of additional scientific information to assist our understanding of this issue! Thanks ever so much.

Julie P. (149)
Monday November 26, 2012, 8:04 pm
Thanks J.L. Here's a little more:

"in some forest types (e.g., Douglas-fir, ponderosa pine, and moist tropical) large intact blocks of healthy, mature forests or nondecadent, old-growth forests are less susceptible to catastrophic fires than young or
fragmented forests. Landscapes dominated by these types buffer and dampen the spread of crown fires and hence preserve the forest structure. Once some threshold proportion of the landscape becomes fragmented and permeated by flammable young forests or grasses, the potential exists for a self-reinforcing cycle of catastrophic fires–an absorbing landscape crosses a threshold and becomes a magnifying one."

"More than 100 million trees are destroyed each year to produce junk mail. 42% of timber harvested nationwide becomes pulpwood for paper.
Reduce global warming. The world’s temperate forests absorb 2 billion tons of carbon annually. Creating and shipping junk mail produces more greenhouse gas emissions than 9 million cars....
•The pulp and paper industry is the single largest consumer of water used in industrial activities in developed countries, and it’s the third-largest industrial greenhouse gas emitter (after the chemical and steel industries).
•The average adult receives 41 pounds of junk mail each year. 44% goes to the landfill unopened."

"Deforestation: Every year, the magazine industry in the US deforests an area the size of the Rocky
Mountain National Park for the production of 12 billion magazine copies-that’s one tree per second.

Energy: The U.S. pulp and paper industry is the second largest industrial consumer of energy.

Climate Change: The production of magazine paper creates nearly seven million tons of greenhouse
gasses each year.

Solid Waste: Each year, three billion magazines never reach a reader’s hands. Placed end to end, those
magazines would circle the Earth 20 times.

Toxics: The pulp and paper industry uses dozens of chlorine-based chemicals, which along with their
by-products are harmful to human health and the environment."

North American's consume an average of approximately 500 pounds of paper yearly. The global average is approximately 120 pounds.


JL A. (275)
Monday November 26, 2012, 8:22 pm
Thanks for all the updated/current numbers on the paper industry Julie! Reminded me of the years I faithfully wrote remove me from your list, put every scrap in the postage paid envelope adding as much gravel as would fit and mailed it back (I was assured they would have to pay excess postage on it) and succeeded in reducing junk mail received considerably. I knew there was something special about ponderosa pine, and welcomed learning exactly what it is (they grow in places I have frequented). Other pieces validated some choices I've made as well--thank you for highlighting choices we might not have thought of for becoming 'greener' and reducing our environmental impacts.

Robert O. (12)
Tuesday November 27, 2012, 1:28 am
Thank you!

Frans Badenhorst (552)
Tuesday November 27, 2012, 1:50 am
very good post, thanks Julie...... just loooooooooooove trees....

Danuta Watola (1206)
Tuesday November 27, 2012, 2:59 am

Past Member (0)
Tuesday November 27, 2012, 3:42 am
Thanks, noted.

Joanne S. (0)
Tuesday November 27, 2012, 4:25 am
Thank you.

Donnaa D. (14)
Tuesday November 27, 2012, 5:17 am
thank you noted

June M. (105)
Tuesday November 27, 2012, 5:55 am
noted thanks for sharing J.L

Ben Oscarsito (316)
Tuesday November 27, 2012, 5:59 am
I now one thing; -We can NEVER plant too many trees! I have in mind to plant a thousand trees before the end of this year. So far I have planted 958, and I think I will make it with a little help from my friends...
Now, let us Plant many, many, many Trees for The Children of Tomorrow!
Thank You! Gracias! Merci! Obrigado! Grazie! Tack!

JL A. (275)
Tuesday November 27, 2012, 12:03 pm
Robert, Frans, John. Joanne, Donnaa, June and Ben: you are all very welcome (and Julie does indeed deserve all our thanks!). You are SOOOO right Ben and have identified one thing we all can do to help address the issue!

Melania Padilla (179)
Tuesday November 27, 2012, 2:27 pm

JL A. (275)
Tuesday November 27, 2012, 2:39 pm
You are welcome Melania!

Theodore Shayne (56)
Tuesday November 27, 2012, 4:34 pm

Siti R. (12)
Wednesday November 28, 2012, 3:10 am
noted and thanks!

Karen R. (87)
Wednesday November 28, 2012, 3:28 am
We need trees!

JL A. (275)
Wednesday November 28, 2012, 8:43 am
You are welcome Siti!
You cannot currently send a star to Karen because you have done so within the last week.

Tamara Mendelson (1)
Wednesday November 28, 2012, 10:18 am

Dave C. (216)
Thursday November 29, 2012, 8:03 pm
sad and scary.
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