Forest Health





Native forest insects and diseases are generally of less concern when they exist at non-damaging population levels. It is when populations of these native species increase beyond an acceptable threshold, or when alien or native species behave invasively that concerns arise. If ecological or economic damage results in measurable impacts—such as a decline in ecosystem health or large reduction in the available wood fibre—then the insect or disease outbreak is seen as being a disturbance and active management intervention may be considered (Natural Resources Canada, n.d.).

In 2009, the Yukon Forest Management Branch (FMB) implemented a risk-based approach to forest health monitoring that is consistent with the Canadian Council of Forest Ministers National Forest Pest Strategy (NFPS). The objectives of the approach are:

  • to provide a Yukon-wide overview of forest health issues;
  • to focus monitoring activities on high-risk forest health agents in high value forest regions; and
  • to contribute to the NFPS goals, one of which is developing early detection and reporting capacity of forest health pests.

Yukon FMB produces an annual forest health report which presents the biotic and abiotic disturbance(s) detected by the annual forest health survey. The survey is performed in a different area (forest health management zone) each year.

For a full assessment of Yukon forest health issues, see the Yukon Forest Health Reports.


Map 1: Forest Health Zone Map Shows areas flown from 2009-2016 and planned surveys for 2017 and 2018.




What is happening?

As part of its risk based forest health monitoring program in 2016, the FMB completed:

  • Aerial overview surveys, monitoring of the Yukon/ BC border zone for mountain pine beetle (MPB), pheromone bait deployment for MPB, and egg mass surveys of Large Aspen Tortrix.
  • Aerial overview surveys were conducted over forest health zone (FHZ) 2 and parts of FHZ 1 (Refer to Map 1).
  • 2015 aerial surveys found a significant presence of Large Aspen Tortrix, a defoliator of Aspen, in FHZ 1. (see Map 1 – Large Aspen Tortrix monitoring) Affected parts of this zone were re-flown in 2016 to monitor the outbreak.
    Large Aspen Tortrix
  • In 2016, the area affected by Large Aspen Tortrix declined compared to the area affected in 2015 in FHZ 1 (see Map 1- Large Aspen Tortrix monitoring).
  • In 2016, an increase was noted in the area affected by Aspen decline. The majority of Aspen decline was found in combination with Large Aspen Tortrix.
  • Egg mass sampling was conducted in 2016 to predict the following year’s population levels. Severe defoliation is predicted in a small section of the Dezadeash/ Kathleen Lake Corridor, with nil to minor defoliation in the surrounding areas.


Moderate Large Aspen Tortrix defoliation near Partridge Creek NW of Stewart Crossing. (The brownish, pinkish hue of the aspen stand is associated with Large Aspen Tortrix.) Insert: close up of the defoliation


Aspen Serpentine Leafminer

  • Aspen Serpentine Leafminer is another defoliator of Aspen that was recorded in the aerial survey of zone 2.
  • In 2016, the area affected by leafminer remained relatively un-changed from the previous survey done in 2012, with the exception of a marked decline in defoliation intensity.
  • Eighty-two per cent of the area infested was identified as a combination of aspen serpentine leaf miner and aspen decline.
  • Overall, area infested by the leafminer continues to decline across Yukon, with 2016 marking the fifth consecutive year with minimal activity by this insect pest.


Moderate aspen serpentine leafminer, north of Pelly Crossing near Diamain Lake. The silver tinge of the aspen stand is associated with Aspen serpentine leafminer.


Aspen Decline

  • Aspen Decline or dieback refers to mortality or damage to forests due to unknown causes, including a possible combination of biotic and abiotic factors.
  • In 2016, 160,010 hectares exhibited symptoms of aspen decline in FHZ 2 and the highway corridor between Mendenhall and Dezadeash Lake in FHZ 1. The vast majority was in combination with defoliators.


Aspen decline SE of Dawson City, an area where moderate aspen decline was mapped in 2015 and symptoms remains visible in 2016. Insert: Aspen decline symptoms observed from the air – thinning crowns and stem mortality, 2016.

Birch Defoliation

  • Light defoliation was observed over 847 hectares northeast of Beaver Creek, mostly between the Donjek River and Mount Cockfield, with a few isolated spots south and east of Carmacks.
  • Defoliation likely occurred from a Birch leafroller.


Thinning crowns on birch near Donjek Creek, NE of Beaver Creek, FHZ2 Note the clean aspen on south aspect.

Table 1: Comparison of recorded forest health disturbances in FHZ 2 (2011, 2012, and 2016). Areas within the recent Large Aspen Tortrix outbreak in FHZ 1 and FHZ 3.



Zone 2

Zone 1

Disturbance Type












Aspen serpentine leaf miner






Aspen serpentine leaf miner/large aspen tortrix






Aspen serpentine leaf miner/aspen decline






Large aspen tortrix






Large aspen tortrix/aspen serpentine leaf miner






Large aspen tortrix/aspen decline






Birch leaf roller






Spruce beetle






Western balsam bark beetle






Willow blotch miner






Northern spruce engraver beetle






Pine needle disease












Aspen decline












Drought - spruce






Drought - aspen


















Pest Complexes






Aspen decline/serpentine leaf miner






Porcupine/lodgepole pine beetle









Taking action


Proactive Management of Mountain Pine Beetle (MPB)

2016 is the sixth consecutive year that FMB has been conducting aerial surveys in northern BC. In 2010, when aerial surveys were initiated, MPB populations and subsequent pine mortality within the Rocky Mountain Trench of B.C. were very high (within 150 kilometers of Yukon border). Since that time, severe winter cold has killed beetle broods within the trees. That combined with no large feeder population in northern BC has arrested significant northward movement of MPB populations. FMB continues to monitor the border zone as per our MPB monitoring strategy (See Map 1).


Main body of Mountain Pine Beetle infestation 150 km south of Yukon border, observed at its peak of infestation in Rocky Mountain Trench BC, in 2011.


Since 2009, FMB has been setting up and monitoring 15 pheromone bait tree stations in southern Yukon to detect the presence of MPB (Map 2). These pheromone baits do not attract MPB over long distances, but will draw them to the baits if they are already in the area. They also do not attract other species of bark beetles. No presence of MPB was found in 2016.


MAP 2: Mountain Pine Beetle monitoring bait trap locations in Southern Yukon and B.C.


Pheremone placed on the North side of the tree.


FMB field staff setting up pheromone bait traps.


Aspen Decline

Since the aerial surveys were started in 2009, FMB has observed an increase in the presence of Aspen decline, particularly in the North (i.e. Dawson and Mayo). Further monitoring is required to identify factors that contribute to Aspen decline.

Blowdown Monitoring

In spring of 2016 there was a wind event East of Watson Lake that resulted in blowdown in both Aspen and Spruce stands. Patches of blowdown ranged from 2 – 25 ha in size. A total of 108 ha of spruce leading and 350 ha of Aspen leading blowdown was mapped. As part of identifying the potential Spruce Bark Beetle risk, FMB conducted aerial surveys of the blowdown. Further ground and aerial monitoring will be conducted in 2017.


Moderate to severe defoliation caused by large aspen tortrix.



Data quality

  • From 1950 to 1995, the Forest Insect and Disease Survey (FIDS) was conducted by the Canadian Forest Service (CFS). From 1995 both CFS and FMB conducted aerial surveys monitoring Spruce Bark Beetle near Haines Junction.
  • Aerial overview surveys are the primary tool for monitoring forest health in Yukon. In 2009, with National Forest Pest Strategy funding, FMB adopted the aerial overview survey program and has been conducting annual aerial surveys at a landscape level to identify both biotic and abiotic disturbances.
  • As of 2013, all five forest health zones in Yukon were monitored by aerial overview survey. Baseline data has been collected from each forest health zone. Hence, from 2014 on, mapping resolution moved from eight kilometer gridlines to 12 kilometer gridlines. During the monitoring of the forest health zones, researchers may select disturbances for further monitoring in the same year. If necessary, these disturbances are identified as ongoing monitoring areas to be included along with the forest health zones scheduled for aerial surveys during the current year.
  • FMB’s forest health program contains ground survey protocols to predict insect population trends.


Conducting Large Aspen Tortrix egg mass surveys to predict population trends, FMB cutting top branches to inspect for egg mass. Insert: Close-up of eggs mass on upper side of leaf. Note black spot indicating parasitism.





Forest Management Branch Website: http://www.forestry.gov.yk.ca/

Forest Health Brochures featuring main pests and pathogens of Yukon: http://www.emr.gov.yk.ca/forestry/insects_disease.html

Natural Resources Canada. n.d. Forest pest management. (2016, March 23). Available from: http://www.nrcan.gc.ca/forests/fire-insects-disturbances/pest-management/13361