Sudden oak death diminishes after dry winter, but infection remains rampant

By Guy Kovner
Sudden oak death has killed up to 50 million trees and 100 million more may be infeceted, according to new research.

A dry winter curtailed the presence of a deadly forest pathogen this year in Sonoma County and 13 other Northern and Central California counties, but experts still expect the oak-killing disease to spread and warned landowners to be vigilant.

Since the mid-1990s, sudden oak death has killed up to 50 million trees from Big Sur to southwest Oregon and is entrenched in the woodlands, spreading rapidly after wet winters and slower during dry years.

“It’s constant, it’s emerging,” said Richard Cobb, an assistant professor of forest health at Cal Poly San Luis Obispo. “It’s probably going to get a lot worse.”

Cobb said Monday he’s about to publish his estimate of tree mortality, 90 percent of which are tanoaks and most of the rest coast live oaks. Another 100 million trees may be infected by the insidious pathogen that typically takes one or two years to produce symptoms in the infected trees, he said.

The pathogen can be spread by human footprints and nursery plants, but in nature it rides on water droplets blown from the leaves of bay laurel trees, a host species that abounds among the oak and tanoak trees susceptible to the disease.

“We know there’s a lot of disease out there,” said Matteo Garbelotto, director of the forest pathology and mycology laboratory at UC Berkeley, which has organized annual sudden oak death surveys, known as the SOD Blitz, since 2008.

This year’s survey found the estimated rate of infection — based on lab analysis of leaves collected from bay laurels and tanoaks — at 3.5 percent throughout the 14-county region, a marked decline from 12.8 percent last year.

Sonoma County, divided into three areas, also showed sharp declines, which Garbelotto said were anticipated because the 2017 survey, conducted in the wake of two straight wet winters, found the highest infection rate ever recorded in 11 years.

But the survey conducted in May found another consequence — the presence of oaks showing symptoms of infection had increased to 12.2 percent throughout the region, up from 9.4 percent last year.

Next year’s rate should be higher, Garbelotto said, coming two years after the 2017 rains and matching the time it takes for symptoms, such as bleeding cankers in oak tree bark, to appear.

Source: Sudden oak death diminishes after dry winter, but infection remains rampant – The Press Democrat, 2018-10-16

Hygroscopic aerosols linked to forest decline

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.

Source: Hygroscopic aerosols linked to forest decline – Brinkwire, 2018-09-25

An arboreal murder mystery: What is killing beech trees?

By Gabriel Popkin
The trees are dying in three states and Canada, and scientists still don’t know why.

Ohio biologist John Pogacnik admits to mixed feelings about having discovered the latest disease imperiling a major American tree.

Pogacnik first noticed American beech trees with striped and shriveled leaves in 2012 during a routine survey of forests owned by his employer, Lake Metroparks. He didn’t think much of it at first: Just a few trees looked sick, and it had been a strange year, with an unusually warm winter and dry spring.

By the next summer, Pogacnik was seeing ailing trees throughout the six-county region in northeast Ohio where his agency manages more than 35 parks. He alerted colleagues at the Ohio Division of Forestry and the U.S. Forest Service.

“I’m glad to have found it, to just put it out there and let people know,” he said. “But it’s still not the greatest feeling in the world.”

Beech leaf disease has now popped up in nine Ohio counties, two other states and Canada, and its spread shows no sign of slowing. The disease has already felled young saplings; mature trees, some hundreds of years old, appear to be on the brink of death. Scientists fear the beech could soon face a plague as serious as those that have devastated chestnut, elm, hemlock and ash trees. “It has all the signs of a significant, emerging pathogen,” said Constance Hausman, a biologist at Cleveland Metroparks.

Scientists are gearing up to fight back, but they face a major challenge: Nobody knows what beech leaf disease is. Searches for a virus, bacteria or fungus — all common tree pathogens — have come up empty. Researchers are facing an arboreal murder mystery.

Source: An arboreal murder mystery: What is killing beech trees? – The Washington Post, 2018-07-08

Pine beetles from Jasper National Park now infesting commercial forest

By Bob Weber
A massive and uncontrollable buildup of mountain pine beetles in Jasper National Park is starting to explode into commercially valuable forests along its boundaries.

Foresters along the park’s edge have seen a tenfold increase in beetle infestation in just months, and some scientists wonder if Parks Canada could have done more to control the invasion a few years ago.

“They decided to consider the pine beetle a ‘native disturbance agent,”‘ said Allan Carroll, who has studied the beetles since the late 1990s and directs the University of British Columbia’s Forest Science program. “In other words, Jasper was not intending to do much about it.”

No end to pine beetle battle in Alberta, experts say
In an emailed statement, Parks Canada said it has had a beetle management plan for the park since 2015 that includes prescribed burns and tree removal.

Too little, too late, said Carroll.

“Just that hesitation intrinsic to producing a management plan precluded any effective outcomes.”

Source: Pine beetles from Jasper National Park now infesting commercial forest – CBC News, 2017-11-17

Friend or foe? Be on the lookout for invasive insects

Insects, both beneficial and disruptive, have always been front-of-mind for the people growing our food. Of particular interest in today’s world are invasives: insects that are not native to a region and whose introduction (whether intentional or accidental) is likely to cause harm to our environment, our economy or human health. Or already has.

A 2016 report in Nature Communication estimates that the annual economic impact of invasive insects on goods and services in North America is at least $27.3 billion. And this, say the authors, is likely an underestimation because determining the economic impact of invasives can be particularly difficult. “Most cost estimates are disparate, regionally focused, cover variable periods and are not always grounded in verifiable data,” write the authors. Additionally, the spread and the impact of invasive insects is likely to increase in coming years due to climate change, rising human population densities and intensifying international trade. But, say the authors, there is a way to minimize the impact: increased surveillance, containment and public awareness. In other words: To protect our local farmers, food systems and economies, we – the general public – need to pay attention to the bugs around us.

Source: Friend or foe? Be on the lookout for invasive insects – The Chronicle-Express, 2017-05-14

The painful riddle of forest thinning plan

By Peter Aleshire
Fire season looms.

Every high country community quivers on the cusp.

So the U.S. Forest Service will on Thursday hold a meeting on its plan to use thinning projects and controlled burns across a million acres of Rim Country to dramatically reduce both tree densities and wildfire risk.

One little problem: The Four Forest Restoration Initiative (4FRI) the plan envisions has fallen years behind schedule and is struggling to make a dent on the hundreds of thousands of acres of projects already approved.

The Forest Service awarded the first 4FRI contract five years ago for an initial 300,000 acres out of a total of 2.6 million eventually targeted. The Forest Service shifted the contract from Pioneer Forest Products to Good Earth AZ after a year, with no projects completed. So far, Good Earth has completed thinning projects on about 8,500 acres out of the 60,000 called for in the original schedule. Good Earth has said it plans to thin 30,000 acres annually, but so far has had trouble lining up enough trucks and capacity at small-wood sawmills to come anywhere near that pace.

Source: The painful riddle of forest thinning plan – Heber/Overgaard | wmicentral.com, 2017-04-14

Beetles making difference in woolly adelgid fight

By David Singleton
A beetle is winning the battle against the hemlock woolly adelgid at Nay Aug Gorge.

Almost 20 years after the woolly adelgid arrived at Nay Aug Park and started threatening the hemlocks in and around the gorge, officials believe they’ve finally gained the upper hand against the invasive, tree-killing pest, thanks in large part to a predatory beetle called S. tsugae.

“I think we caught it in time, and we have turned the corner. There is no doubt about it,” city forester Tony Santoli said. “I have seen great improvement.”

Since it started working with Santoli in 2011, Tree-Savers, a private company with offices in Waymart that specializes in saving endangered hemlocks, has released about 10,000 S. tsugae beetles at Nay Aug as part of an effort to eradicate the woolly adelgid and restore the park’s weakened hemlocks to health.

Like the woolly adelgid, the beetle — its full scientific name is Sasajiscymnus tsugae — is native to Japan. It is the woolly adelgid’s natural enemy, feeding on the tiny insect’s eggs.

A beetle is winning the battle against the hemlock woolly adelgid at Nay Aug Gorge.

Source: Beetles making difference in woolly adelgid fight at Nay Aug Park – The Times-Tribune, 2017-04-15

Researchers predict increasing decline of hemlock as winters warm

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.

Source: UMaine-led team predicts increasing decline of hemlock as winters warm – UMaine News – University of Maine, 2017-04-07

Fires, thinning create healthier forest

by Peter Aleshire
Patchy.

That’s what you want.

Whether it comes to bark beetles, forest fires, migrating birds, elk or deer — what you want are forests with patches thick with trees, open areas and hillsides burned decades ago.

This conclusion has emerged from a series of recent studies on bark beetles and tree densities.

The studies support the underlying logic of the Four Forest Restoration Initiative (4FRI), an ambitious effort to use a reinvented, small-tree logging industry to thin the forest and diversify the landscape.

The project has lagged far behind the schedule needed to thin the first installment of 300,000 acres, mostly because the 4FRI contractor Good Earth has struggled to build up the infrastructure needed to thin 30,000 to 50,000 acres annually.

However, recent research validates the underlying blueprint for 4FRI, which would dramatically lower tree densities in the ponderosa pine forests, while creating a landscape with denser patches separated by a wide-open, thinned forest.

Source: Fires, thinning create healthier forest = Payson Roundup, 2016-04-04

Will climate change affect forest ecology?

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.

Source: Will climate change affect forest ecology? – Burlington Free Press, 2017-03-12