Jeff Mulhollem, Pennsylvania State University
Genes in green ash trees that may confer some resistance to attacks by the emerald ash borer express themselves only once the tree detects the invasive beetle’s feeding, according to Penn State researchers.
Knowing this, geneticists may be able to selectively breed trees to strengthen them and perhaps move the resistance response earlier to ward off the beetles’ onslaught, explained John Carlson, professor of molecular genetics.
Green ash, an ecologically and economically valuable tree species native to eastern and central North America, is under severe threat from the rapid invasion of emerald ash borer, a wood-boring beetle native to Asia. Penn State scientists and others are trying to save the species.
Prior observations in a green ash provenance trial—an experiment to see how plants adapt—planted at Penn State in 1978 by Kim Steiner, professor of forest biology and director of The Arboretum at Penn State, and colleagues in the U.S. Forest Service, show that a very small percentage of ash trees survive emerald ash borer infestations, seemingly because their tissues do not nourish and perhaps even sicken the beetles.
“Emerald ash borer probably entered the provenance trial unnoticed around 2008 and trees started showing symptoms of attack by 2012,” Carlson said. “All but eight or nine of the approximately 1,800 trees that Kim planted have subsequently been killed by the beetles.”
Ash trees succumb after adult beetles lay eggs on their bark. When the eggs hatch, the larvae bore into the bark and feed on the transportation tissues of the tree. This disrupts the movement of nutrients and water within the tree, girdling it and causing death.
“To better understand the response of green ash trees to emerald ash borer, we compared gene expression data for resistant versus susceptible green ash genotypes exposed to attack by the beetles,” said Carlson, director of Penn State’s Schatz Center for Tree Molecular Genetics. “By comparing RNA-sequence data from stems attacked by emerald ash borer to multiple tree tissues under other stresses, we could identify differences in the gene expression profiles specific to emerald ash borer resistance.”
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.
The ʻŌhiʻa tree, with its companion lehua blossom, is found only in Hawaiʻi, and is the most common of our Islands’ native trees. It is the keystone of the Hawaiʻi forest, critical to the ecology of our watersheds and sacred in Hawaiian culture. And now it is under attack, with new species of fungi killing trees on two islands.
By Lucy Sherriff
The native ʻōhiʻa is sacred to Hawaiians as a cultural touchstone and ecological underpinning for the state’s lush forests and abundant wildlife.
HONOLULU — A deadly fungus threatens one of Hawaii’s most beloved and important species, the ʻōhiʻa tree, and those believed responsible for introducing the threat to the tree in the first place are now being asked to help save it — tourists.
The native ʻōhiʻa is sacred to Hawaiians as a cultural touchstone and ecological underpinning for the state’s lush forests and abundant wildlife. The flowering evergreens that can tower to 85 feet comprise 80 percent of the state’s canopy, covering 1 million acres, and its nectar sustains birds and insects found nowhere else on Earth.
Now, public agencies and private citizens are trying to avoid biological and economic catastrophe by proclaiming war against a deadly fungal disease coined “rapid ʻōhiʻa death,” or ROD, that is swiftly destroying the trees. What’s more, invasive species like the miconia tree, native to North and South America and called the “green cancer” of Hawaii’s forests, are choking out the ʻōhiʻa.
The federal government has attempted to stop the fungus and tackle invasive species by imposing a quarantine on Hawaii Island and carrying out extensive tests to learn how the fungus spreads, but it has yet to find a solution. Hawaiian organizations, communities and scientists are now stepping in.
Gunstock Ranch, a horse riding stable and tourist destination on Oahu, is replanting native trees, although not the ʻōhi‘a yet. After conducting a survey on 80 acres of its land in 2016, and finding just two native species, owner Greg Smith established a Hawaiian “legacy forest,” where visitors can plant trees and monitor their growth online.
“Our hope is that as our guests plant and dedicate a tree they will form a new connection to the land and Hawaii and leave knowing that they made a difference,” Smith said.
By Stephen Koranda
Plants sold at more than 60 stores in Kansas were infected with a disease that kills oak trees. The Kansas Department of Agriculture said sudden oak death was confirmed in hundreds of rhododendrons in the state, and the agency is asking Kansans to destroy any potentially infected plants.
The infected rhododendrons came from a nursery in Oklahoma and were sold in 10 states, including Kansas and Missouri. In Kansas, the plants were sold during April, May and June at 60 Walmart stores and the Home Depot in Pittsburg.
This is the first time sudden oak death has been found in the state. It’s a disease that has heavily damaged some forests on the west coast, where it was discovered in the mid-1990s.
“It is just devastating when it gets to oaks,” Kansas State University Professor Cheryl Boyer said in an interview. “It will kill the whole mature trees very, very quickly.”
Ryan Armbrust, with the Kansas Forest Service, noted in a statement that many of the state’s oak trees are from varieties that are less susceptible.
“But there are millions of red, black, pin, shumard, blackjack, shingle and other oaks that could be impacted should this disease gain a foothold in the state,” he said.
By Grace Neumiller, Keller Leet-Otley, and Tommaso Wagner
Brown ash trees, also known as black ash, are critically endangered throughout the state of Maine. The emerald ash borer, a parasitic beetle that has already killed ash trees across the United States, was first detected in Maine last May — several years before it was anticipated. Faced with these ongoing threats, the Wabanaki tribes — Mi’kmaq, Maliseet, Passamaquoddy, and Penobscot — have been leading the defense of brown ash trees in Maine.
Native to wetlands, but often planted in New England towns, brown ash trees play a critical role in basket-weaving practices, particularly to those of the Wabanaki.
Jennifer Neptune, a member of the Penobscot Nation, director of the Maine Indian Basketmakers’ Alliance, and co-curator of an upcoming art exhibition at Colby College, says that brown ash wood is integral to indigenous basket weaving traditions. Not only does the wood possess flexibility and strength, but the brown ash is also considered to be the source of life in Wabanaki creation stories, central to Wabanaki culture. Under threat of local and global extinctions, brown ash tree endangerment jeopardizes the livelihoods of basketmakers and cultural practices of the Wabanaki.
The emerald ash borer is known by entomologists by its acronym: EAB. If you’re an insect aficionado or a tree lover, you likely already know this name. For the rest of you, it’s a name you will know soon enough. It is the cause of arguably the most catastrophic current tree death events in the history of North America.
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 Adrian Higgins
A pear seedling selection named Bradford was cloned by the gazillion to become the ubiquitous street tree of America’s postwar suburban expansion. Then it turned invasive.
Carole Bergmann pulls her small parks department SUV into an aging 1980s subdivision in Germantown, Md., and takes me to the edge of an expansive meadow. A dense screen of charcoal-gray trees stands between the open ground and the backyards of several houses. The trees are callery pears, the escaped offspring of landscape specimens and street trees from the neighborhood. With no gardener to guide them, the spindly wildlings form an impenetrable thicket of dark twigs with three-inch thorns.
Bergmann, a field botanist for the Montgomery County Parks Department, extricates herself from the thicket and in the meadow shows me that what I take to be blades of grass are actually shoots of trees, mowed to a few inches high. There are countless thousands, hiding in plain sight in Great Seneca Stream Valley Park. If it were not cut back once a year, the meadow would become like the adjacent screen, wall upon wall, acre upon acre of black-limbed, armored trees worthy of Sleeping Beauty’s castle.
“You can’t mow this once and walk away,” said Bergmann, who began her 25-year career in the department as a forest ecologist but has been consumed by an ever-pressing need to address the escape of the Bradford pear and other variants of callery pear, a species that originated in China, along with other invasive exotics.
By Neil Shaw
JOHANNESBURG — One of the world’s largest urban forests is under threat from a tiny beetle.
The polyphagous shot hole borer is thought to have made its way to Johannesburg from Southeast Asia on packing crates or through the trade in plant materials.
Trudy Paap, a forest pathologist at the University of Pretoria, discovered the beetle in the Pietermaritzburg Botanical Gardens last year. She published her discovery in the journal Australasian Plant Pathology, calling it part of “the surge in the global spread of invasive forest pests” because of globalization.
The beetle has since moved to Johannesburg, 200 miles away, and spread across its urban forest, which according to the Massachusetts Institute of Technology initiative Treepedia has the world’s sixth-largest green canopy cover.
Today, many of Johannesburg’s estimated 6 to 10 million trees are dying, a crisis obscured only by the current winter season. Some of the infected trees have the telltale holes the 2-millimeter-long beetle makes in their bark.
“This beetle doesn’t actually eat the trees,” Paap said. Instead it carries a fungus that blocks the vessels that transport water and nutrients, “which ultimately leads to die-back and death of the tree.”
Though scientists don’t know just how many trees have died from the beetles’ invasion, the outlook for Johannesburg is grim: “The city is going to lose a lot of trees.”
The trees do not have an evolved resistance to the polyphagous shothole borer, unlike in Asia where the beetles naturally occur.
It is the older, more established trees that are at risk, said arborist Neil Hill. “So that’s going to leave a gap in the landscape. And if we don’t start to plant straight way with new trees that gap is going to become more and more of a concern as far as urban blight, pollution, aesthetic beauty.”