Alaska Forest Health Highlights 2019
Scroll down to read about key forest health issues in Alaska & view interactive survey maps.
Introduction
Hemlock sawfly defoliation damage on northern Admiralty Island in 2019. Defoliation turned large swaths of hemlock forest yellow-brown.
There are 126 million acres of forestland in Alaska, representing 17 percent of the Nation's forests. In 2019, aerial surveyors mapped over 1.1 million acres of forest damage from insects, diseases, declines, and abiotic agents on the 24.4 million acres surveyed. The interactive aerial detection survey map at the end of this story map allows users to view and filter aerial survey data from 2019. This story map includes: forest insect highlights, forest disease and decline highlights, invasive plant highlights, and aerial detection survey results.
Follow links to our Forest Health Protection website to learn more about specific damage agents and to view our annual Forest Health Conditions reports . Ground data collection is critically important to forest health monitoring, as some important types of damage cannot be mapped from the air. Below, our new cumulative ground survey map allows users to select damage categories, damage agents, host tree or shrub species, and survey years of interest to view all relevant records. If you are using a mobile device, click on the link in the window below to view this map and explore the dataset.
Ground observations across years can now be filtered and displayed in our web map! CLICK HERE to view the interactive map dashboard in a new window. For assistance, contact Loretta Winton at loretta.winton@usda.gov.
Forest Insect Highlights
Hemlock Sawfly
A hemlock sawfly outbreak that began in 2018 has greatly expanded across Southeast Alaska. We aerially mapped nearly 400,000 acres of sawfly damage in western hemlock forests in 2019. Severe defoliation was most prevalent on Prince of Wales, Mitkof and Kupreanof Islands, and the outbreak extends north to Juneau.
Severe hemlock sawfly defoliation near Angoon, Admiralty Island.
Hemlock sawfly damage aerially mapped in 2018 and 2019.
In 2019, we detected abundant hemlock sawflies in ground survey plots, but low levels of western blackheaded budworm, another hemlock defoliator. As long as these two insects are not defoliating together, hemlock mortality from this outbreak is expected to be limited.
US Forest Service Biological Technician, Isaac Davis, examines defoliators that have dropped onto a beating sheet as a means of assessing relative species abundance and larval health.
Gregarious hemlock sawfly larvae munching on hemlock needles.
Parasites that target different hemlock sawfly life stages will help to end the outbreak. We are monitoring these natural population controls to assess how long the outbreak is likely to last, and will continue to track tree damage and mortality in severely affected forests.
Watch our video about hemlock sawfly and the current outbreak to learn more!
Background photo: An upward view of defoliated western hemlock tree crowns near Juneau.
Spruce Beetle
New spruce beetle mortality was mapped on 140,000 acres in 2019, compared to nearly a million total acres in 2017 and 2018. Despite the substantial decrease in acreage, a spruce beetle outbreak is ongoing in Southcentral Alaska. New damage expanded in nearly all directions from previously impacted forests.
Aerially mapped mortality from spruce beetle 2016-2019.
Much of the active spruce beetle mortality was detected as individual attacked trees or clumps of trees in a sea of dead spruce killed earlier in the outbreak. In some areas, where the outbreak has been most severe, the supply of susceptible white spruce has been exhausted. As beetles run out of large white spruce, the preferred host, they move into smaller-diameter white spruce and black spruce forests.
Beetles collected in traps are identified and counted. Spruce beetles, shown here, are brown to black and about 5mm long.
A handful of spruce beetles collected from a monitoring trap in 2018. The abundance of beetles in traps does not always correspond to the degree of damage.
Multiple ongoing trials are underway in Southcentral Alaska to determine if high-value spruce trees can be protected by applications of systemic insecticides or by external applications of semiochemicals during an outbreak. Study partners include the Pacific Southwest Research Station (USFS), the Alaska DNR Division of Forestry, and Arborjet Inc.
For more information on spruce beetle biology and management, see the cooperatively managed website www.alaskasprucebeetle.org .
Background photo: Spruce trees killed by spruce beetle at the South Denali Overlook.
Birch Leafminer
Birch leafminer damage was aerially mapped across 290,000 acres statewide, 2.5 times more than last year. The bulk of the defoliation occurred in the Matanuska-Susitna Valley and on the Kenai Peninsula, with considerably less defoliation mapped in the Interior. While the damage is unsightly and caused by invasive defoliating insects, mining activity is not known to kill trees.
Birch leafminer damage mapped in 2019 during aerial and ground surveys, with the modeled distribution of birch in Alaska.
Late season flights in 2018 detected infestations far beyond major population centers and roadways, where damage was previously thought to be concentrated. In 2019, flights were scheduled in August to improve detection of remote infestations of these invasive defoliators.
Birch defoliation in the lower Matanuska-Susitna Valley in August 2019. Photo credit: Jason Moan, DNR-DOF.
Three invasive birch leafminers are established in Alaska. In 2019 ground surveys, the amber-marked birch leafminer was most common in the Interior, the late birch leaf edgeminer in the Matanuska-Susitna Valley, and both pests were equally abundant on the Kenai.
Birch leafminers can be identified based on the location of mines and presence of frass/droppings within mines. More than one species of leafminer can occur on a leaf. Birch leaf edgeminer creates mines along leaf margins, while the amber-marked birch leafminer creates mines containing dark brown frass.
Background photo: Severe birch leaf miner defoliation.
Balsam Woolly Adelgid
In June 2019, balsam woolly adelgids were discovered infesting ornamental subalpine firs in Juneau, the first detection in Alaska. These invasive, sap-sucking insects are native to Europe and have caused extensive damage to fir trees in the United States. They are easily spread by wind, birds, and the movement firewood, nursery plants, and Christmas trees. Firs do not occur in Juneau's natural forests, but are popular ornamental trees; the natural range of subalpine fir and Pacific silver fir occur elsewhere in Southeast Alaska, including northern Lynn Canal.
Waxy, white balsam woolly adelgids on subalpine fir near Dimond Park in Juneau.
A multi-agency team responded to the infestation by delineating its extent in Juneau. The team will host workshops this winter to teach property owners how to identify infestations and about best management practices for fir trees. Most infested trees are located on City and Borough of Juneau property and will be removed and destroyed this winter. Treatment was delayed until winter, when the risk of spread during treatment is negligible because the insect is in a non-migratory life stage.
Discoloration and dieback symptoms of balsam woolly adelgid on subalpine fir.
Background photo: Forest health experts from the Forest Service and Alaska DNR examine heavily infested firs near Dimond Park in Juneau during surveys in fall 2019.
Forest Disease & Decline Highlights
Aspen Running Canker
Aspen running canker is an important tree killer in the boreal forests of Alaska. Over the last several years, we have been working to determine the distribution, cause, and impacts of this destructive disease. We are investigating what causes the disease by isolating and growing microorganisms from diseased tissue, then wounding and inoculating healthy trees with each of the candidate fungi. Researchers at the University of Alaska Fairbanks are partnering with us to evaluate how trees respond to infection. In collaboration with researchers at the University of Nebraska Lincoln, we have found one fungus that consistently causes more disease than the other thirteen we've tested.
US Forest Service Forest Pathologist, Lori Winton, scrapes away aspen bark of freshly felled trees to reveal margins between healthy and canker-killed tissue.
A lesion caused by aspen running canker expanded by nearly a centimeter within three days in Interior Alaska. The dead canker tissue is orange and black, while the healthy bark tissue is green to red.
US Forest Service Biological Technician Dana Brennan uses a staple gun to wound aspen trees for inoculation trials. We are inoculating healthy trees with candidate fungi we isolated from diseased trees.
Background photo: Damage from aspen running canker along the Yukon River in Interior Alaska. Note the large number of fallen trees in the foreground.
Spruce Needle Rust
Spruce needle rust , a fungal disease that infects new needles of spruce, gives spruce trees an other-worldly orange tinge. This summer, a large outbreak was aerially mapped across nearly 115,000 acres in southwestern Alaska, especially in Wood-Tikchik State Park and south along the Nushagak River to Bristol Bay. Spruce needle rust damage was also common and severe in Southeast Alaska. Peak damage occurs in August after most surveys are complete.
Spruce needle rust mapped through aerial survey and ground observations in 2019. The later survey in SW Alaska improved aerial detection.
Spruce needle rust near Juneau, Alaska in 2019.
This disease causes flashy outbreaks but does not typically kill trees. It affects the newest needles and severe damage usually doesn't occur at the same location for consecutive years. The causal fungus has life cycle stages on Labrador tea, so damage tends to be most severe where this understory host plant is also present.
Orange spores and fruiting structures of spruce needle rust on white spruce in western Alaska. Photo credit: Jason Moan, Alaska DNR-DOF.
Background photo: Spruce needle rust causes spruce to appear orange from the air. Photo credit: Jason Moan, Alaska DNR-DOF.
Yellow-Cedar Decline
Yellow-cedar decline , caused by freezing injury of yellow-cedar roots in the absence of insulating snowpack, is the most significant threat to yellow-cedar populations in Alaska. In October 2019, Federal protection for yellow-cedar under the Endangered Species Act was deemed unwarranted. The U.S. Fish and Wildlife Service's listing decision is available in the Federal Register (Vol. 84, No. 194). The Species Status Assessment was completed in March 2018.
We found that yellow-cedar is experiencing a decline primarily caused by a changing climate in the core of its range...Despite [these] impacts...the species is expected to persist in thousands of stands across its range...into the foreseeable future.
-U.S. Fish and Wildlife Service Listing Decision ( full text available here )
Sheila Spores (USFS) plants a yellow-cedar seedling on Prince of Wales Island as part of common garden trial. Planting yellow-cedar on sites with deep soils can promote its long-term survival.
The silvery bark of a yellow-cedar on Shelter Island near Juneau, Alaska.
We continue to monitor yellow-cedar decline in old-growth forests and in stands managed for timber. About 20,000 acres of actively dying yellow-cedar forests were mapped in 2019. Young-growth yellow-cedar decline (in 35-45 year old forests managed for timber) is an emerging issue, particularly where soils are wet or shallow. In monitoring plots installed last year in the most severely affected managed stands, one-third of yellow-cedar crop trees had crown discoloration damage. The condition of symptomatic trees is expected to worsen, since declining trees tend to die gradually in old-growth forests unless they are attacked by secondary bark beetles.
Active yellow-cedar decline mapped during the 2019 aerial survey, 33 managed young-growth stands in which decline symptoms have been detected, and 2019 survey flightlines.
A recently killed yellow-cedar tree in a managed stand on Wrangell Island.
Background photo: A mix of dead and dying yellow-cedar trees on Chichagof Island in Southeast Alaska.
Invasive Plant Highlights
European Birdcherry
Unfortunately, highly invasive European birdcherry trees (Prunus padus) have been planted widely across Alaska from Juneau to Fairbanks. They can create mono-cultures when they spread into natural forests, outcompeting and replacing native trees and shrubs. Cyanide within the plant tissue can be toxic to moose and other herbivores. Across the state, invasive species experts and local citizens have been working to address and mitigate damage from birdcherry.
The boundary between private property and a treated forest managed by the Municipality of Anchorage. The photo was taken before native trees leafed out; native trees survived the treatment. Before treatment, almost all understory plants were birdcherry. Photo Credit: Tim Stallard, Alien Species Control, LLC.
An infestation of more than 3,000 birdcherry trees covering several acres was discovered in Juneau, and treatment planning is needed. On the Kenai Peninsula, Chugach National Forest personnel treated a small infestation along Grant Lake. In Hope, nearly all of the planted landscape trees have been controlled, with the community outreach and treatment effort spearheaded by a local resident. Large-scale birdcherry treatments and efficacy studies continue in Anchorage, along with volunteer outreach events such as the 9th Annual Weed Smackdown. In Talkeetna and along the Susitka River, the Community Council is working with the Upper Susitna Soil and Water Conservation District to to encourage residents to remove ornamentally planted birdcherry trees.
European birdcherry in full bloom.
Background photo: European birdcherry along a stream in Anchorage, Alaska.
Elodea waterweed
The invasive aquatic plant Elodea was found in another Alaskan lake on the Kenai Peninsula, Sandpiper Lake, in 2019. This brings the total number of infested lakes detected on the Kenai to six. With an aggressive early detection and rapid response strategy, the Kenai Peninsula Cooperative Weed Management area partners appear to have successfully eradicated Elodea from five of the six lakes, a major feat. Treatment of the newest infestation is slated for spring.
An Elodea sample collected from Chena Slough.
Farther north, Fairbanks Soil and Water Conservation District (FSWCD) surveyed 33 lakes and found no new infestations. Four sites were treated with herbicide, resulting in significant reductions in Elodea. There are plans to treat additional sites in 2020. Outreach efforts continued, including sign installations and education events targeted at specific groups, such as float plane users, village councils, and lakeside communities.
Fluridone pellet treatment application in Chena Lake in 2019. Photo credit: Colin McKenzie.
USFS Plant Ecologist, Trish Wurtz, surveys for Elodea below the surface of Chena Slough near Fairbanks. Trish retired in June 2019 and we welcome Betty Charnon to the position.
For more information , see the Alaska-DNR Elodea website .
Background photo: Kenai National Wildlife Refuge personnel treating Beck Lake with liquid fluridone. Photo credit: John Morton, Kenai National Wildlife Refuge.
Orange Hawkweed
Girdwood’s Alyeska Ski Resort has had a long simmering infestation of orange hawkweed, which extended across 30 acres in 2018. Thanks to funding from a Copper River Watershed Project Invasive Plant Mini-grant, and years of community outreach efforts by local partners, this infestation was treated in May and June 2019. Post-treatment, this large hawkweed population was reduced by more than ninety percent. There are likely isolated plants beyond treated areas; therefore, follow-up efforts will be needed to find and control additional plants in the coming years to ensure that the treatment remains effective.
Orange hawkweed (Hieracium aurantiacum) near Girdwood, Alaska.
Background photo: A biker pedals through a large patch of orange hawkweed on mountain biking trails at Alyeska Ski Resort in Girdwood. Photo credit: Heather Thamm, USFS.
Aerial Detection Survey
Preparing to depart the Lake Hood Seaplane Base in Anchorage in 2018.
Aerial surveys are conducted by float plane annually in mid-summer, when damage is typically at its peak. Surveyors map current forest damage at a speed of 120 mph and an altitude of about 1000 ft using digital sketch-mapping software on a tablet.
Survey tablets display the plane's location over a topographic base map to improve mapping accuracy. Surveyors draw polygons on the screen to depict the damage observed, noting the host tree species, damage type, and damage severity. Whenever possible, mapped damage is evaluated on the ground during or soon after the survey. Surveyors depend on known damage signatures, the unique appearance of tree hosts affected by specific types of damage. If you're using a mobile device, click the link in the window below to view the interactive 2019 Alaska Aerial Detection Survey Map.
Click on the 2019 Alaska Aerial Detection Survey map to begin interacting. The information button to the top right of the map opens instructions on map tools. To open the map in a new window, CLICK HERE . For assistance, contact Robin Mulvey at robin.mulvey@usda.gov.
We hope you enjoyed this forest health update from our USFS Forest Health Protection team in Alaska. If you have questions or feedback, please contact Robin Mulvey at robin.mulvey@usda.gov. Our website provides abundant information and resources, as well as contact information for forest health experts across the state in Juneau, Anchorage, and Fairbanks.
