By PASSANT RABIE
Bigleaf maple trees in Washington state are on the decline. Researchers are on the hunt for the cause, and climate change is turning into a lead suspect.
Daniel Omdal has driven past the same bigleaf maple tree for decades, often stopping his car to take pictures of its full, expansive crown. In the past few years, however, the tree has started to look more lopsided, with bare branches and patches in its crown with little to no growth.
To Omdal, a forest pathologist, it seemed like an obvious case of an insect infestation. If not, perhaps some kind of disease: a damaging fungus, wilt or a rogue bacterium. Whatever it was, it wasn’t isolated to one tree. The extent of sick bigleaf maples was alarming, and Omdal wasn’t the only one who was worried.
Omdal’s colleagues at the Washington State Department of Natural Resources, where he has worked since 1997, had noticed the same symptoms in many other bigleaf maples. So had many residents of the region, who called the state to report their concerns. The issue had also been occurring nationwide, with reports of sharp declines of urban tree populations in different states, such as the oak tree in Southern California. In Washington, the problem was hard to miss: Bigleafs, also known as Oregon maples, are a staple of the Pacific Northwest landscape.
“These calls became more frequent, I couldn’t so easily dismiss the concerns,” Omdal says. In 2011, he became part of a state-led team investigating the bigleaf die-offs.
The group discovered that about 40 percent of bigleaf maple trees in Washington state are declining, says Jacob Betzen, a graduate student at the University of Washington’s School of Environmental and Forest Sciences, who has been working with the investigative team for the past two years.
The first suspect on their list was Armillaria, a fungus that causes the roots of the tree to rot. But when the team tested hundreds of trees for it, most of their results came back negative. Then, the researchers tested for another fungus called verticillium wilt. Also negative. Often, a few trees would be infected, but it was never widespread enough to be the primary cause of the species’ decline.
Omdal collected soil samples to test in the lab to look for other causes. Every time his team followed a new lead, it didn’t pan out. “We would come to a dead end,” Omdal says.
Patrick Tobin, Betzen’s advisor and a specialist in disturbance ecology, added, “It’s been puzzling, there’s no smoking gun here.”
Then Betzen noticed something curious about the die-offs. They are much more common in developed landscapes and areas that are warmer, drier and closer to roads. That led to a new suspect: climate change. “It seemed probably related to recent weather patterns, it’s getting hotter and drier in Washington in recent years,” Betzen says. The group’s results won’t be published until Betzen concludes his research at the end of the year, but Tobin is confident that the key driver causing bigleaf maple die-offs is, in fact, climate change.
By Brad Plumer
A new study found that the United States could store enough carbon in natural landscapes to offset all the cars and trucks on the road.
When people think of potential solutions to global warming, they tend to visualize technologies like solar panels or electric cars. A new study published on Wednesday, however, found that better management of forests, grasslands and soils in the United States could offset as much as 21 percent of the country’s annual greenhouse gas emissions.
At the high end of the projections, that would be roughly equivalent to taking every single car and truck in the country off the road.
The paper, published in the journal Science Advances, identified a number of promising strategies, like replanting trees on degraded lands, changing logging practices to better protect existing forests and sequestering more carbon in farmland soils through new agricultural techniques.
“We’re not saying these strategies are a substitute for getting to zero-carbon energy; we still need to do that too,” said Joseph E. Fargione, a scientist at the Nature Conservancy and lead author of the study. “But we think that natural climate solutions generally get overlooked. And we found a lot of opportunities here to help mitigate climate change.”
By Josephine Marcotty
As Minnesota’s ash trees fall to the invasion of emerald ash borer in the next decade, the forest that borders the 72-mile stretch of the Mississippi River in the Twin Cities metro area is expected to lose one-fifth of its canopy.
Turns out that’s not all bad.
Conservation groups that work in the 54,000-acre Mississippi National River and Recreation Area are using that environmental disaster to thwart a much larger one on the way — climate change.
By replacing ash with other kinds of trees, as well as bushes and other plants, they hope to establish a forest that is more likely to thrive in a future of higher average temperatures and much more erratic precipitation.
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 John Sullivan, Office of Engineering Communications
Researchers using satellite imaging have found much greater than expected deforestation since 2000 in the highlands of Southeast Asia, a critically important world ecosystem.
Zhenzhong Zeng, a postdoctoral researcher at Princeton University and the lead author of a July 2 article describing the findings in Nature Geoscience, said the researchers used a combination of satellite data and computational algorithms to reach their conclusions. The report shows a loss of 29.3 million hectares of forest (roughly 113,000 square miles or about twice the size of New York state) between 2000 and 2014. Zeng said that represents 57 percent more loss than current estimations of deforestation made by the International Panel on Climate Change. He said most of the forest has been cleared for crops.
Because forests absorb atmospheric carbon, and burning forests contribute carbon to the atmosphere, loss of forests could be devastating. An accurate estimation of forest cover also is critical for assessments of climate change. Zeng also said transformation of mountainous regions from old forest to cropland can have widespread environmental impacts from soil retention to water quality in the region.
By Damian Carrington, Niko Kommenda, Pablo Gutiérrez and Cath Levett
Global deforestation is on an upward trend, jeopardising efforts to tackle climate change and the massive decline in wildlife.
Global tree cover losses have doubled since 2003, while deforestation in crucial tropical rainforest has doubled since 2008. A falling trend in Brazil has been reversed amid political instability and forest destruction has soared in Colombia.
In other key nations, the Democratic Republic of Congo’s vast forests suffered record losses. However, in Indonesia, deforestation dropped 60% in 2017, helped by fewer forest fires and government action.
Forest losses are a huge contributor to the carbon emissions driving global warming, about the same as total emissions from the US, which is the world’s second biggest polluter. Deforestation destroys wildlife habitat and is a key reason for populations of wildlife having plunged by half in the last 40 years, starting a sixth mass extinction.
By Robinson Meyer
As the consequences of climate change strike across the United States, ecologists have a guiding principle about how they think plants will respond. Cold-adapted plants will survive if they move “up”—that is, as they move further north (away from the tropics) and higher in elevation (away from the warm ground).
A new survey of how tree populations have shifted over the past three decades finds that this effect is already in action. But there’s a twist: Even more than moving poleward, trees are moving west.
About three-quarters of tree species common to eastern American forests—including white oaks, sugar maples, and American hollies—have shifted their population center west since 1980. More than half of the species studied also moved northward during the same period.
These results, among the first to use empirical data to look at how climate change is shaping eastern forests, were published in Science Advances on Wednesday.
By Margaret Nagle
Land managers in New England and eastern New York state have a new tool to help identify eastern hemlock stands at greatest risk for rapid growth decline by evaluating stresses on the trees, including response to the hemlock woolly adelgid and changes resulting from a warming climate.
Today, an estimated 26 percent of the region’s hemlock stands are at high risk. As winters get warmer, the decline will increase, with 43 percent of stands expected to be at high risk, according to a research team led by University of Maine Associate Professor of Forest Resources William Livingston.
The researchers’ comprehensive landscape model maps the varied response to the invasive Asian insect across the Northeast, and identified the site characteristics of stands with the highest potential for tolerance and recovery in order to prioritize management efforts.
Eastern hemlock is a towering foundational species in eastern North American forests valued from southern Canada to Alabama and as far west as Minnesota. But since the mid-20th century, eastern hemlock that can live more than 500 years have been increasingly threatened by the hemlock woolly adelgid that can kill a tree within four years by feeding on its needles and branches, preventing new growth.
Using changes in tree rings — basal area increment (BAI) measurement — in mature hemlock, the researchers quantified annual growth decline in 41 hemlock stands across New England representing a range of infestation density and duration, and species vigor. The model also was applied to 15 hemlock sites in Massachusetts.
Among the findings of the research team using the growth decline metric: Eastern hemlock sited on steeper slopes with increased exposure to solar radiation and warmer January minimum temperatures have a greater probability of experiencing rapid decline.
The results of the study, which involved researchers from UMaine, the University of Vermont and LandVest Inc., in Portland, Maine, were published in the journal Biological Invasions.
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.
A study of Front Range forests burned by wildfires between 1996 and 2003 shows they are not regenerating as well as expected and large portions may become grasslands or shrub lands in coming years.
The paper, published in the journal Ecosphere by former doctoral student Monica Rother and geography professor Thomas Veblen, examined the sites of six low-elevation ponderosa pine forest fires which collectively burned 162,000 acres along the Colorado Front Range between 1996 and 2003. Eight to 15 years after the fires, the researchers expected – based on historical patterns – to see young trees cropping up across the landscape. Instead, 59 percent of plots surveyed showed no conifer seedlings at all and 83 percent showed a very low density of seedlings. Although it is possible that more seedlings will appear in upcoming years, future warming and associated drought may hinder significant further recovery.
“It is alarming, but we were not surprised by the results given what you see when you hike through these areas,” said Rother, who earned her doctorate from CU Boulder in 2015 and works as a fire ecologist at Tall Timbers Research Station in Tallahassee, Florida.