♤♤♤ A VUELO DE UN QUINDE® , EL BLOG! ♧♧♧: Forest Droughts

Mostrando entradas con la etiqueta Forest Droughts. Mostrar todas las entradas

domingo, 24 de abril de 2016

NSF: Earth Week: In a drought, which trees risk death? .- Semana de la Tierra: En una sequía, que la muerte árboles es un riesgo?

Hola amigos: A VUELO DE UN QUINDE EL BLOG., La sequía dejó 225 millones de árboles muertos en el suroeste de EE.UU. en 2002. Nueve años más tarde, que mató a 300 millones de árboles en Texas. El año pasado, 12 millones de árboles murieron en California.
En todo el mundo, un gran número de árboles se están muriendo en el calor extremo y la sequía. Tales matanzas colectivas pueden tener consecuencias importantes para el futuro de los bosques y el clima de la Tierra. En la Semana de la Tierra, los científicos están tratando de entender cómo el calentamiento global podría afectar la frecuencia ocurren los eventos de mortalidad de árboles - y qué tan grave que podría llegar a ser.
Una Universidad de Utah,un biólogo puede ser capaz de ayudar. William Anderegg y sus colegas buscaron patrones en los estudios previos de mortalidad de los árboles y encontraron algunos rasgos comunes que caracterizan las que vivía especies y que murió durante la sequía. Los resultados, publicados hoy en la revista Proceedings de la Academia Nacional de Ciencias (PNAS), pueden ayudar a trazar el futuro de los bosques.

More information.............

http://www.nsf.gov/news/news_summ.jsp?cntn_id=138226&WT.mc_id=USNSF_51&WT.mc_ev=click

Study identifies tree traits that contribute to drought vulnerability

Ponderosa pine on Grand Canyon rim falling over from a drought attack.
Credit and Larger Version

April 18, 2016

Drought left 225 million trees dead in the U.S. Southwest in 2002. Nine years later, it killed 300 million trees in Texas. This past year, 12 million trees died in California.

Throughout the world, large numbers of trees are dying in extreme heat and drought. Such mass die-offs can have critical consequences for the future of forests and Earth's climate. On Earth Week, scientists are trying to understand how a warming climate could affect how often tree mortality events occur -- and how severe they could become.

A University of Utah biologist may be able to help. William Anderegg and his colleagues looked for patterns in previous studies of tree mortality and found some common traits that characterized which species lived and which died during drought. The results, published today in the journal Proceedings of the National Academy of Sciences (PNAS), can help chart the future of forests.

"There are some common threads that we might be able to use to predict which species are going to be more vulnerable in the future," Anderegg says.

Forests in crisis

"With drought projected to increase, predicting tree death is imperative to understanding changes in Earth's forests," says Liz Blood, program director in the National Science Foundation (NSF) Division of Environmental Biology, which funded the research. "This study offers important new insights into how and why trees die from drought, and which trees are at greatest risk."

Worldwide, forests absorb the equivalent of about one-quarter of the carbon dioxide emissions humans produce. So large-scale tree die-offs not only shut down a forest's ability to sequester greenhouse gases but also release some of those gases back into the atmosphere as dead trees decompose.

In climate models, scientists have had difficulty accounting for these changes in carbon dioxide storage. The effect of drought on various species' mortality rates has been difficult to predict. "That launched this search to understand what about a tree's physiology predisposes it to die during a severe drought," Anderegg says.

The researchers combed through 33 published studies of tree mortality that included 475 tree species and more than 760,000 individual trees. The team noted mortality rates for each species, then compared those to 10 tree physiological traits, searching for commonalities.

The traits included typical tree characteristics such as wood density, rooting depth and basic leaf characteristics, and whether the species was evergreen or deciduous. Other traits concerned the hydraulics of how water moves through trees.

Tree 'heart attack'

The researchers found only three traits that significantly predicted tree drought mortality, all of which related to hydraulics.

Roots take in water, which is pumped throughout the tree to hydrate leaves and support photosynthesis. In times of plenty, water moves easily through the tree. But when temperatures increase, evaporation from leaves drives higher water demand.

At the same time, if drought makes water harder to come by, the tree's roots have to pull harder to draw scant moisture from the soil. Tension builds in the tree's "pipes" as they work harder and harder to move water, like a person trying to suck a thick smoothie through a small straw.

At a certain point, tension on the "pipes" becomes so great that bubbles of air enter them and block water flow. The result is called an embolism.

"It's a little bit akin to a tree heart attack," Anderegg says. "You can actually hear this on a hot summer day if you stick a microphone up to a tree -- you can hear little pings and pops as these pipes get filled with air." Blocked pipes lead to tree death.

The three traits Anderegg found that significantly affected tree mortality were:

The point at which a tree loses 50 percent of its hydraulic conductivity due to embolism.
The point at which a tree loses 88 percent of total hydraulic conductivity.
The hydraulic safety margin, the range between the tension of water the tree allows during dry conditions and the tension that causes hydraulic dysfunction.

Other traits did not affect tree mortality nearly as much as these characteristics. Anderegg says trees accustomed to plentiful water, such as trembling aspens, are more susceptible than junipers, which are better adapted to dry conditions.

Signs of climate change

The next step is to incorporate these traits into climate models and forest models to help public and private land managers forecast which trees might be most susceptible to drought.

Anderegg says that recent tree-killing droughts in the western U.S. were marked more by elevated temperature -- a sign of a warming world -- than by a lack of rainfall.

"These widespread tree die-offs are a really early and visible sign of climate change already affecting our landscapes," he says.

-NSF-

Media Contacts Cheryl Dybas, NSF, (703) 292-7734, cdybas@nsf.gov
Paul Gabrielsen, University of Utah, (801) 585-6861, paul.gabrielsen@utah.edu

Related WebsitesNSF Grant: Extreme Events and Ecological Acclimation: Scaling from Cells to Ecosystems: http://www.nsf.gov/awardsearch/showAward?AWD_ID=1340270&HistoricalAwards=false

The National Science Foundation (NSF) is an independent federal agency that supports fundamental research and education across all fields of science and engineering. In fiscal year (FY) 2016, its budget is $7.5 billion. NSF funds reach all 50 states through grants to nearly 2,000 colleges, universities and other institutions. Each year, NSF receives more than 48,000 competitive proposals for funding and makes about 12,000 new funding awards. NSF also awards about $626 million in professional and service contracts yearly.

Get News Updates by Email
Useful NSF Web Sites:
NSF Home Page:
http://www.nsf.gov
NSF News:
http://www.nsf.gov/news/
For the News Media:
http://www.nsf.gov/news/newsroom.jsp
Science and Engineering Statistics:
http://www.nsf.gov/statistics/
Awards Searches:
http://www.nsf.gov/awardsearch/

Dead oak trees line a forest near Mancos, Colorado.
Credit and Larger Version
dead aspen trees near Fairplay, Colorado

These trembling aspen trees near Fairplay, Colorado, were killed by severe drought.
Credit and Larger Version
bare aspens trees

Drought stress felled these trembling aspens near Flagstaff, Arizona.
Credit and Larger Version
Dead trees in the San Juan National Forest near Mancos, Colorado.

Dead trees in the San Juan National Forest near Mancos, Colorado.

Dead trees from recent droughts in the San Juan National Forest near Mancos, Colorado.
Credit and Larger Version
dead aspens trees throughtout a forest

Drought near Grand Junction, Colorado, resulted in the deaths of many trembling aspens.
Credit and Larger Versión

The National Science Foundation (NSF)
Guillermo Gonzalo Sánchez Achutegui
ayabaca@gmail.om
ayabaca@hotmail.com
ayabaca@yahoo.com
Inscríbete en el Foro del blog y participa : A Vuelo De Un Quinde - El Foro!

jueves, 25 de febrero de 2016

NSF: Increasing drought threatens almost all U.S. forests .- El aumento de la sequía amenaza a casi todos los bosques de Estados Unidos

Hola amigos: A VUELO DE UN QUINDE EL BLOG., hemos recibido información de la Fundación Nacional de Ciencias de Los Estados Unidos, nos dice: "Bosques en todo el país están sintiendo el calor de la creciente sequía y el cambio climático, según un nuevo estudio realizado por científicos de 14 instituciones de investigación.
"En las últimas dos décadas, las temperaturas más cálidas y precipitaciones variables han aumentado la severidad de las sequías forestales en gran parte del territorio continental de Estados Unidos", dijo James Clark, autor principal del estudio y científico ambiental en la Universidad de Duke.
Clark y sus colegas publicaron su trabajo en la revista Global Change Biology.
"Mientras que los efectos han sido más pronunciada en Occidente, nuestro análisis muestra virtualmente que todos los bosques de Estados Unidos están experimentando cambios y son vulnerables a futuras caídas", dijo Clark.
Es una tarea difícil predecir lo que estos bosques se verá como en 20 años, según los investigadores.

More information....

http://www.nsf.gov/news/news_summ.jsp?cntn_id=136815&WT.mc_id=USNSF_51&WT.mc_ev=click

Forests nationwide feeling the heat

dried trees in a forest of pinons in the U.S. Southwest.

Drought has left little but skeleton trees in a forest of pinons in the U.S. Southwest.
Credit and Larger Version

February 22, 2016

Forests nationwide are feeling the heat from increasing drought and climate change, according to a new study by scientists from 14 research institutions.

"Over the last two decades, warming temperatures and variable precipitation have increased the severity of forest droughts across much of the continental United States," said James Clark, lead author of the study and an environmental scientist at Duke University.

Clark and colleagues published their paper today in the journal Global Change Biology.

"While the effects have been most pronounced in the West, our analysis shows virtually that all U.S. forests are now experiencing change and are vulnerable to future declines," Clark said.

It's a tall order to predict what these forests will look like in 20 years, the researchers say.

Drought across the U.S. West

Drought-induced forest diebacks (the deaths of entire communities of trees known as stands), bark beetle infestations, and wildfires are already occurring on large scales across the West. Many models predict droughts are likely to become more severe, frequent and prolonged across much of the U.S.

Evidence is also mounting that climate is changing faster than tree populations can respond.

As conditions become drier and warmer, many tree populations, especially those in Eastern forests, may not be able to expand into new, more favorable habitats, fast enough to keep up.

"Most forest research is carried out at local study sites, where trees are individually catalogued and measured," said Henry Gholz, a program director in the Division of Environmental Biology at the National Science Foundation (NSF), which supported the research. "This approach risks 'missing the forest for the trees.'"

The new results show that changes in both western and eastern U.S. forests could happen quickly under drier conditions in the future, said Gholz.

"Prolonged drought affects wildfire risks, species distribution, forest biodiversity and productivity, and virtually all goods and services provided by forests," Clark said, "so there is a pressing need to know what is happening now, what might happen in the future, and how we can manage for these changes."

Forests and drought, from A to Z

The new paper addresses this need by providing a comprehensive overview of current and projected drought effects on forests nationwide, how they vary by region, and which management practices could help to partially mitigate adverse effects.

The paper also identifies critical gaps in our knowledge base that hinder scientists' ability to predict the pace and extent of future drought effects on forests.

"We currently have a pretty good handle on predicting the impacts of climate change and drought on individual trees," Clark said. "Ecologists have identified many of the important differences between species that explain how they respond differently to drought."

But, he said, uncertainty still exists about what might happen at the species-wide or stand-wide levels, particularly in Eastern forests. "These are the scales where we really need reliable predictions so forest managers can take steps now to help reduce large-scale adverse future effects."

Without a stronger basis for understanding how the complex interactions among trees, species and environmental conditions work at broader scales, even the most sophisticated current models can provide only limited guidance, Clark said. "That's where we need to focus our efforts now."

Major co-authors of the paper are Louis Iverson and Christopher W. Woodall of the U.S. Forest Service, as well as scientists with the U.S. Geological Survey, the University of Vermont, the University of California (UC), Santa Barbara, Sarah Lawrence College, the University of Michigan, the University of Arizona, Ohio State University, Harvard Forest, UC Davis, Northern Arizona University and the Swiss Federal Research Institute.

-NSF-

Media Contacts Cheryl Dybas, NSF, (703) 292-7734, cdybas@nsf.gov
Tim Lucas, Duke University, (919) 613-8084, tdlucas@duke.edu

Related WebsitesNSF News: Cause of California drought linked to climate change: https://www.nsf.gov/news/news_summ.jsp?cntn_id=132709
NSF News: Drought, heat likely to affect U.S. West's power grid: http://www.nsf.gov/news/news_summ.jsp?cntn_id=135021
NSF Discovery: Earth Week: Bark beetles change Rocky Mountain stream flows, affect water quality:
http://nsf.gov/discoveries/disc_summ.jsp?cntn_id=130951
NSF Discovery: Ghosts of Forests Past: Bark Beetles Kill Lodgepole Pines, Affecting Entire Watersheds:
http://www.nsf.gov/discoveries/disc_summ.jsp?cntn_id=128398
NSF Discovery: Born during a drought: Bad news for baboons: http://nsf.gov/discoveries/disc_summ.jsp?cntn_id=134000&org=NSF

Wildfires, with flames fanned by drought, are happening on large scales across the U.S. West.
Credit and Larger Version
Dying ponderosa pines in a forest in California

Dying ponderosa pines in a forest in California

Dying ponderosa pines cover a hillslope during the third year of a warm drought in California.
Credit and Larger Version
drying leaves in a linden tree.

Symptoms of drought are appearing across the country, such as "leaf scorch" on this linden tree.
Credit and Larger Version
view of dried and green trees mixed in a forest