By Beth Gavrilles
The longleaf pine forests of the southeastern U.S. depend on frequent fire to maintain their structure and the diversity of plants and animals they support. New research from the University of Georgia has found that fire may be playing another, unexpected role: releasing excessive nitrogen that appears to have accumulated as a legacy of prior land use.
“It was not what we were expecting,” said senior author Nina Wurzburger, an associate professor in the Odum School of Ecology. “We first were wondering whether there was enough nitrogen fixation to balance nitrogen losses from fire, and now our hypothesis is that fire might be necessary to remove excess nitrogen from these ecosystems. We basically turned the question on its head.”
“We came to the conclusion that fire might be getting rid of excess nitrogen,” said Wurzburger. “Most of the longleaf pine that exists today has been planted, and those areas have legacy effects of agriculture or grazing or fire exclusion. Our research is suggesting that all those things, and nitrogen deposition too, have put too much nitrogen in the ecosystem. So maybe we should think about fire as a management tool to remove nitrogen that accumulated historically, and to help return these ecosystems to their natural nitrogen-poor state.”
Understanding the interacting role of fire and historical disturbances in longleaf ecosystems is important for several reasons, including carbon sequestration and the conservation of biodiversity: longleaf savannas can contain more than 40 species of plants in a square meter, and harbor a number of rare species of plants and animals, including the federally endangered red cockaded woodpecker.
By Amanda Kolson Hurley
In the 1960s, America fell in love with a new tree: the Bradford pear. Cultivated from Asian stock by scientists at the U.S. Department of Agriculture, Bradford pears display clouds of pretty blossoms in the spring and garnet leaves in the fall, and are hardy enough to grow just about anywhere. Thinking they had found the perfect ornamental tree, homeowners and public-works departments planted Bradford pears up and down the nation’s streets for decades, especially in the East, South, and Midwest.
Then the relationship soured. Bradfords are apt to split and break during storms, and they have a short life span, only 15 or 20 years. Although they are technically sterile, the trees cross-pollinate with other cultivars of the Callery pear species (Pyrus calleryana), producing fruit that splats all over sidewalks. And despite their delicate appearance, the blossoms emit a foul odor that’s been compared to rotting fish (among other things).Cities and states are trying to remove Bradford pears‚ but the “weed trees” have already intruded deep into some forests, a biologist warns.
Once admired for its hardiness, the Bradford pear is now considered an invasive species, which grows even in poor conditions, proliferates fast—thanks to birds that dine on its fruit and spread the seeds—and crowds out native species.
Cities are trying to put an end to the tree’s mischief. Pittsburgh’s Urban Forest Master Plan prohibits planting Bradford pears. This March, Fayetteville, Arkansas, started offering a bounty to anyone who cuts one down. (They can get a free native tree to replace it.)
The bad news is it’s not only in developed areas where the trees threaten to choke biodiversity. Theresa Culley, head of the Department of Biological Sciences at the University of Cincinnati, warns that wild Bradfords and other kinds of Callery pears are making inroads into Eastern forests.
by Elyse Catalina, University of Maine
A mouse scampers through the forest, stopping suddenly at the sight of a tree seed on the ground. A potential meal. And a dilemma.
The mouse must decide if it should eat the seed immediately. Or hide it in a safe place for consumption when food is scarce. Or pass it up in hopes of something better.
Many factors determine what the mouse will do next, including how abundant the seeds are and if the rodent is a fan of that variety.
Personality is another element that might play a role in what the mouse decides, according to a University of Maine researcher.
How animals react to an environment that is transforming due to human behavior and climate change is at the core of research being conducted by Alessio Mortelliti, an assistant professor of wildlife habitat ecology at UMaine.
One study Mortelliti and his students are pursuing focuses on how individual personalities of small mammals affect their response to global change.
Like humans, animals have a personality, according to Mortelliti.
“Anyone that has a pet knows they have a personality,” he says. “It’s the same for squirrels, mice and voles.”
Within a species, individuals can be aggressive or shy, more or less social, Mortelliti explains.
“We’re looking at how this individuality—their own way of being—affects the way they respond to changes in their environment made by humans,” he says of wild small mammals.
When a mouse finds a seed, the decision it makes affects more than the mouse. If the seed is eaten immediately, any chance of a plant sprouting from that seed is gone. If the mouse decides to move and store the seed, a plant has a chance to grow.
Mortelliti believes that by modifying the environment, humans may be favoring certain personality types over others and, in turn, altering the course of evolution and the shape of the forest.
By Steven S. Perakis and Julie C. Pett-Ridge
Tree species that form symbioses with nitrogen-fixing bacteria can naturally fertilize forests by converting atmospheric nitrogen gas into plant-available forms. However, other mineral nutrients that plants require for growth are largely locked in bedrock, and are released only slowly into soil. We used strontium isotopes to trace nutrient sources for six common tree species in a temperate rainforest, including one species from a globally widespread genus known for high rates of biological nitrogen fixation. We found that trees capable of fixing atmospheric nitrogen gas were also best able to directly access mineral nutrients from bedrock. This gives nitrogen-fixing trees the unique ability to provide the full suite of essential nutrients required to fuel growth and carbon uptake in forest ecosystems.
By Amber Dance
Forests are resilient, but researchers wonder if climate change will outpace their adaptations.
Trees bowed to 45-degree angles and flying leaves crisscrossed the sky as Hurricane Florence ravaged North Carolina’s coast and inland regions in mid-September 2018. The storm, which peaked as a Category 4 hurricane before making landfall near Wilmington as a Category 1, deluged parts of the state with nearly three feet of rain. It stripped the leaves off black walnuts, crape myrtles, and their entwining wisterias, especially on the north and northeast sides of the trees, which bore the full brunt of the 100-plus-mile-per-hour wind gusts. An estimated 1.25 million acres of timber, valued at nearly $70 million, suffered varying degrees of damage.
Whoppers like Florence are a reality that North Carolina—not to mention the rest of the Eastern seaboard and the Caribbean—may have to get used to in the near future. Historically, a given location might only see such destructive hurricanes every few decades. But with global temperatures on the rise, the risk that a fledgling storm system will grow to “major” status, defined as category 3 and above, is likely to climb. Warming oceans mean more water vapor in the air, and that vapor is what fuels the storms. “One of the signals that we expect from climate change is that the strongest hurricanes will get stronger,” says Gary Lackmann, an atmospheric scientist at North Carolina State University in Raleigh.
What does that mean for trees? The scene in the woods after Florence was one of seeming devastation. In every direction, trees, branches, and brush littered the ground. Yet just a few weeks after the storm, the stripped trees sprouted fresh leaves and flowers. It may have been autumn, but the trees already had leaf and flower buds in waiting for the upcoming spring, explains Jim Slye, assistant regional forester with the state forest service in Goldsboro. Re-leafing after storms helps keep the trees’ circulation going, and flowering allows trees to drop seeds in case they end up succumbing to storm damage. The trees won’t necessarily die, though; tree ring studies make it clear that many survived past storms.
By Dan Zukowski
A large chunk of the country’s forests were harmed in 2015 by wildlife—77 percent due to deer. Bringing back an apex predator could help staunch the bleeding.
From the peak of Mt. Rausu, a clear view of the Shiretoko Peninsula opens from the Okhotsk Sea on the west to the Pacific Ocean on the east. Below, a dense green boreal forest of conifers, maples, and birch hides hundreds of brown bears and 590,000 sika deer. Japanese wolves once roamed this wilderness but their primeval howls fell silent here, and throughout Japan, more than a hundred years ago.
Narumi Nambu is working to bring wolves back to Japan.
“An apex predator is essential for sustainability of an ecosystem, and in Japan it was a wolf,” she writes in an email. Nambu volunteers for the Japan Wolf Association. Her work earned her the “Who Speaks for Wolf” award at the International Wolf Symposium in Minnesota, where she recently spoke.
She explained that, without the presence of natural predators like wolves, two-thirds of Japan’s 30 national parks are showing signs of deer-induced injury.
Shiretoko National Park, a UNESCO World Heritage Site, has a deer problem, as does much of Japan. According to the most recent annual report by the Japan Forestry Agency, 8,000 hectares of the country’s forest were harmed in 2015 by wildlife—77 percent of it due to deer. All told, deer were responsible for $53 million in damage.
By JoAnna Klein
The grove of 47,000 quivering aspen trees in Utah is being diminished by mule deer, foraging cattle and human mismanagement.
On 106 acres in Fishlake National Forest in Richfield, Utah, a 13-million-pound giant has been looming for thousands of years. But few people have ever heard of him.
This is “the Trembling Giant,” or Pando, from the Latin word for “I spread.” A single clone, and genetically male, he is the most massive organism on Earth. He is a forest of one: a grove of some 47,000 quivering aspen trees — Populus tremuloides — connected by a single root system, and all with the same DNA.
But this majestic behemoth may be more of a Goliath, suggests a study published Wednesday in PLOS ONE. Threatened by herds of hungry animals and human encroachment, Pando is fighting a losing battle.
The study, consisting of recent ground surveys and an analysis of 72 years of aerial photographs, revealed that this unrealized natural treasure and keystone species — with hundreds of dependents — is shrinking. And without more careful management of the forest, and the mule deer and cattle that forage within him, the Trembling Giant will continue to dwindle.
By Carl Zimmer
Islands of greenery, called refugia, survive even the worst fires, sheltering species and renewing charred landscapes.
Forests have burned in spectacular fashion this year. From California to Colorado, Portugal to Greece, photographers have captured terrifying images of infernos soaring into the sky and spreading to the horizon.
The fires left scenes of ashen destruction, but they did not wipe out everything. Scattered about the ravaged landscapes were islands of trees, shrubs and grass that survived unharmed.
It’s easy to overlook these remnants, which ecologists call fire refugia. But they can be vital to the long-term well-being of forests. These havens shelter species that are vulnerable to fires. Afterward, they can be starting points for the ecosystem’s regeneration.
“Those trees are lifeboats,” said Meg Krawchuk, a fire ecologist at Oregon State University.
Writing recently in the journal BioScience, Dr. Krawchuk and her colleagues argued that it’s urgent to better understand fire refugia, because they may be seriously threatened in future decades by climate change. Without them, many species may become threatened and the surrounding ecosystems may take longer to recover from wildfires.
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.
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.”