Hygroscopic aerosols — particles in the air that attract water — could be causing forest decline around the world, according to experiments performed in Germany. Researchers believe that aerosol accumulation on trees enables thin bridges of liquid to form between the leaf interior and the leaf surface, causing the plants to dry out much more rapidly.
“In the atmosphere, aerosols act as cloud condensation nuclei,” says Juergen Burkhardt of the University of Bonn, Germany. “Deposited aerosols on leaf surfaces act almost the same way but attract water from inside the plant.”
Plants have developed sophisticated mechanisms for taking up carbon dioxide from the air for photosynthesis without losing too much water but, as the scientists note, it’s a delicate balance. And one that appears to be upset by rising levels of airborne particles.
“Global aerosol concentrations have roughly doubled compared with natural conditions, and the concentration increase over the continents is even higher,” says Burkhardt. “Our results show that aerosols deposited on leaves interfere with this delicate balance, pointing to a direct mechanism by which air pollution can reduce the drought tolerance of plants.”
Burkhardt and colleagues grew three species of tree — Scots pine, silver fir and common oak — for two years in two greenhouses, one ventilated with ambient air and the other fed with air filtered to remove 99% of aerosols. Seedlings grown under filtered conditions had superior drought tolerance to those raised in ambient air, the team found.
Diversity is strength, even among forests. In a paper published in Nature, researchers led by University of Utah biologist William Anderegg report that forests with trees that employ a high diversity of traits related to water use suffer less of an impact from drought. The results, which expand on previous work that looked at individual tree species’ resilience based on hydraulic traits, lead to new research directions on forest resilience and inform forest managers working to rebuild forests after logging or wildfire.
Surprisingly, says Anderegg, a forest’s hydraulic diversity is the predominant predictor of how well it can handle a drought.
“We expected that hydraulic traits should matter,” he says, “but we were surprised that other traits that a lot of the scientific community have focused on weren’t very explanatory or predictive at all.”
By Daisy Dunne
Forests containing several tree species could store twice as much carbon as the average monoculture plantation, research finds.
A study looking at the carbon storage of forests in southern China finds that each additional tree species introduced to a plantation could add 6% to its total carbon stocks.
The findings suggest that afforestation programmes – which aim to plant trees to “suck” CO2 out of the atmosphere – should switch from using just one plant species to a more diverse mix, a study author tells Carbon Brief.
Planting a diverse range of trees could also bring many co-benefits, the author adds, including providing habitats for a larger range of animals.
However, the relatively small scale of the experiment may have led researchers to overestimate the relationship between tree species diversity and carbon storage, other scientists tell Carbon Brief.
By Morgan Erickson-Davis
Nations are hurrying to reduce greenhouse gas emissions and slow global warming, and one way they’re going about this is by encouraging the protection of forests. Trees trap carbon in their biomass and in the soil, and it’s hoped that keeping them in the ground will keep their carbon out of the atmosphere.
Climate-focused forest conservation policies and programs tend to be focused on rainforests. Covering vast areas, rainforests have earned the moniker “lungs of the planet” for their ability to sequester carbon dioxide while producing oxygen.
But pound for pound, other types of forest give rainforests a run for their money. A hectare of mangrove, for instance, can store four times more carbon than can a hectare of rainforest. And now, new research shows that even temperate forests in cities may be able to sequester nearly as much carbon as a similarly sized area of rainforest.
The study was conducted by a team of scientists from University College London, who mapped the carbon stores of areas of tree cover in the London Borough of Camden. Their results were published recently in the journal Carbon Balance and Management.
The team used remotely sensed LiDAR (which stands for “Light Detection and Ranging”) data that provided high-resolution information about tree structure. Armed with specific numbers on the dimensions and extent of Camden’s aboveground biomass (i.e., the parts of trees that aren’t underground), the researchers were able to estimate how much carbon is contained in each pocket of urban forest.
“Urban trees are a vital resource for our cities that people walk past every day,” said lead author Phil Wilkes. “We were able to map the size and shape of every tree in Camden, from forests in large parks to individual trees in back gardens. This not only allows us to measure how much carbon is stored in these trees but also assess other important services they provide such as habitat for birds and insects.”
Their results indicate Camden’s trees contain more carbon than estimated by previous studies. And while, as a whole, the borough’s median carbon density is on the low side when compared to many natural ecosystems – roughly equivalent to subtropical steppe – its urban forests are carbon storage powerhouses. The maximum value they uncovered was in a large, 320-hectare park called Hampstead Heath. There, carbon density approaches that of tropical rainforest.
By Kathleen Masterson
A new University of Vermont study finds that harvesting trees in a way that mimics old growth forests not only restores critical habitat for animals and plants, but also stores a surprising amount of carbon…
The “old growth” engineering technique succeeded in creating diverse habitats. But the kicker, Keeton says, is that it has also allowed the forest to store a significant amount of carbon, much more than several other conventional tree selection harvesting techniques. That’s key to fighting climate change.
Now, forests that are left alone — with no trees harvested — store the most carbon. But Keeton’s study is finding that it is possible to manage the forest to maximize carbon capture, and still keep it a working forest.
“This greater amount of carbon storage as compared to the conventional treatments was actually a combination of having left more trees behind in the first place, and growth rates that were actually 10 percent higher in this treatment as compared to the conventional harvest,” Keeton says. “And that was really surprising.”
Keeton says after 10 years, the old growth forest management plot stored nearly as much carbon as the unlogged control forest. It came within 16 percent of carbon storage in the unharvested plots.
In the Microbial Sciences Building at the University of Wisconsin-Madison, the incredibly efficient eating habits of a fungus-cultivating termite are surprising even to those well acquainted with the insect’s natural gift for turning wood to dust.
According to a study published today (April 17, 2017) in the journal Proceedings of the National Academy of Sciences, when poplar wood undergoes a short, 3.5-hour transit through the gut of the termite, the emerging feces is almost devoid of lignin, the hard and abundant polymer that gives plant cells walls their sturdiness. As lignin is notorious for being difficult to degrade, and remains a costly obstacle for wood processing industries such as biofuels and paper, the termite is the keeper of a highly sought after secret: a natural system for fully breaking down biomass.
“The speed and efficiency with which the termite is breaking down the lignin polymer is totally unexpected,” says John Ralph, a UW-Madison professor of biochemistry, researcher at the Great Lakes Bioenergy Research Center (GLBRC) and lignin expert. “The tantalizing implication is that this gut system holds keys to breaking down lignin using processes that are completely unknown.”
By Scott Miller
New insights into the impact forests have on surface temperature will provide a valuable tool in efforts to mitigate climate change, according to a new research paper co-authored by Clemson University scientist Thomas O’Halloran.
For the first time, scientists have created a global map measuring the cooling effect forests have by regulating the exchange of water and energy between the Earth’s surface and the atmosphere. In many locations, this cooling effect works in concert with forests’ absorption of carbon dioxide. By coupling information from satellites with local data from sensors mounted to research towers extending high above tree canopies, O’Halloran and his collaborators throughout the world have given a much more complete, diagnostic view of the roles forests play in regulating climate.
Their findings have important implications for how and where different types of land cover can be used to mitigate climate change with forest protection programs and data-driven land-use policies. Results of their study were recently published in the journal Nature Climate Change.
By Jennifer Mcnulty
Tropical reforestation is an important part of the global effort to mitigate climate change, but ecologist Karen Holl says current international goals may be overly ambitious.
“The science and practice of restoration are often quite separate, says Holl, an expert in tropical forest restoration. “Scientific research takes place at a small scale, and we’ve rarely tried to integrate results on the broad scale people are talking about. There’s a mismatch between these really big goals and what’s being done on the ground.”
For decades, tropical forests around the world have been cleared to make way for agricultural and wood products, leaving a wake of environmental devastation behind. Tropical deforestation is a significant contributor to climate change, generating 12-15 percent of global carbon emissions.
To turn that around, the international environmental community has embraced ambitious forest restoration goals: Thirty countries have signed on to restore areas equivalent to the size of Venezuela by 2020; participants at the 2014 United Nations Climate Summit set a global target of nearly four times that by 2030.
Given the current scale of scientific research, those goals may be unattainable, warns Holl, who advises nongovernmental organizations (NGOs) and policy makers around the world and recently authored a “Perspectives” column in Science magazine on this topic.
Most scientific studies are done on relatively small plots—typically a few acres—and results are literally rooted in local conditions, making them difficult to scale up to anywhere near the scope of international agreements.
Restoring vast amounts of forest will require major shifts in planning and science, says Holl.
By Rachel Sargent
For many of us, winter in the Northeast means cold temperatures and piles of snow, drifting through forests and across fields. It’s hard to imagine that winter here could be different, but the prospect of climate change has scientists asking just what our winters might look like in the future – and how those changes might influence forest ecology.
At the U.S. Forest Service’s Hubbard Brook Experimental Forest, scientists are thinking about the year 2100. How much warming will occur isn’t certain, but some projections suggest that average air temperatures in our region may increase 5.5 to 9 degrees over the course of this century. The effects are likely to be complex and are difficult to predict, with benefits and costs for different organisms. Some tree species, for example, may benefit from longer and warmer growing seasons, but they may also sustain root damage from more frequent soil freezing.
It may seem counterintuitive that soils would freeze more often during warm winters. The reason is a projected lack of snow. The blanket of snow that usually accumulates during winter insulates the soil below, preventing it from experiencing the full, sub-freezing temperatures of the air. When warmer temperatures leave a thinner blanket of snow, or none at all, the soil is more likely to freeze when cold snaps strike.