Three moose have died this year in Anchorage due to cyanide poisoning after eating from the European bird cherry tree, also known as Mayday and chokecherry, wildlife officials say.
The Alaska Department of Fish and Game says two calves died in January and a third in February after eating recently frozen buds, branches and berries from the trees. The third moose also ate Japanese yew.
The scientific name for the European bird cherry is prunus padus. Two other types of prunus pervasive in Anchorage, the Canada Red and Amur chokecherries, also have the potential to be poisonous to moose, the department said.
European bird cherry is a deciduous tree that grows 15 to 30 feet high and blooms with fragrant white flowers in late spring or summer. The fruit is a black cherry sought by birds, often attracting flocks of Bohemian waxwings after snow has covered other plants.
Chokecherry trees are dominant along many streams in Anchorage and they can be toxic to animals with segmented stomachs, such as moose, cattle, goats and deer.
The deciduous Japanese yew is planted around Anchorage but is not considered invasive.
The Department of Fish and Game says property owners should cover or dispose of chokecherry and Japanese yew clippings.
Natural chemicals in a moose's rumen -- the first pouch of its many-chambered stomach -- break down the plants and release cyanide gas, killing a calf in as little as 20 minutes, according to wildlife veterinarian Kimberlee Beckmen, who conducted necropsies of the Anchorage moose, which were taken to Fairbanks.
"They're not toxic all the time," she said. "The toxin builds up under certain weather conditions and growing conditions and fertilization."
When the chokecherry freezes, a higher concentration of the toxin goes to the tree's tips, said Ashley Grant, an invasive species specialist with the University of Alaska Fairbanks Cooperative Extension Service office in Anchorage.
"That's the defense for any type of stress," Grant said.
In fall, when the first freeze hits, the toxin builds up and moose are susceptible.
"A week later, that plant won't even be toxic anymore because the toxin dissipates," Beckmen said.
A moose died in 2006 after eating European bird cherry. Biologists found the two cases in January and a third this month while examining carcasses for evidence of disease.
"It's possible that more moose die each spring as a result of cyanide poisoning but we don't have the personnel or resources to examine and test them all," Beckmen said.
An effort is being made to stop the trees' spread in parks and along trails closer to downtown -- Chester and Campbell creeks -- and other places where the Municipality of Anchorage and homeowners have planted it. Prunus trees have been seen in Far North Bicentennial Park and there's a risk that they could spread to Chugach State Park.
"We've been finding that it's displacing native vegetation," said Stephen Nickel, community assistance forester with the state Division of Forestry Community Forestry Program.
Increased diversity is good for urban forests, Nickels said, because diversity allows a forest as a whole to shrug off pests or disease that might affect one species of plant. Invasive species like the prunus trees can disrupt that natural diversity, he said.
Measurements of chokecherry trees at Valley of the Moon Park showed some as old as 30 or 35 years, said municipal forester Scott Stringer. People planting European bird cherry trees back in the day would not have known their potential to out-compete local vegetation, he said.
The trees have pushed out understory vegetation like Canadian dogwood, willow, alder and other trees normally found along Anchorage's waterways, he said.
Stringer advocates more eradication efforts for the invasive tree, but asking nurseries and homeowners not to plant it is also part of the battle, he said.
"In our control efforts, we're trying to contain it where it is . ... But when a bird feeds on a cherry and flies up the creek, then there's a potential it's going to deposit a new seed there."
The trees can be spread not only by air, but also by ground and water when the roots and branches are moved, Stringer said.
"If somebody cut branches in their front yard and threw it in the forest in the back yard, those branches can actually sprout and create new trees," he said.
The trees are popular because they do well with a short growing season and can survive harsh winters, said Nickel, of the Division of Forestry. That's why prunus trees are planted in Alaska, he said.
"Because it was so successful," Nickel said. "But, you know, success can be measured by different ways."
"There's some bad players out there."
Reach Casey Grove at firstname.lastname@example.org or 257-4589.
By CASEY GROVE