ENVIRONMENT YUKON






 

Forests

Forest Health

 

Significance

 

 

Native forest insects and diseases are generally of little 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.

Additionally, the 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. The 2017 report is anticipated to be available in Spring 2018.

 

Map 1: Forest Health Zone Map Shows areas flown from 2009-2017 and planned surveys for 2018 and 2019.

 

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What is happening?

 

  • As a part of FMB’s risk based forest health monitoring program. The following activities were conducted in 2017:
    • aerial overview surveys;
    • monitoring of the Yukon/ BC border zone for mountain pine beetle (MPB);
    • MPB pheromone bait deployment;
    • follow up on the 2016 blowdown event in Watson lake; and
    • risk assessment of decked green spruce in Haines Junction.
  • Aerial overview surveys were conducted over forest health zone (FHZ) 4 and parts of FHZ 1 (Refer to Map 1). Portions of FHZ 1 have been specifically targeted annually since 2012 to map the ongoing large aspen tortrix outbreak.

Forest health disturbances

FMB maps both biotic and abiotic disturbances. Biotic refers to living, such as native and invasive insects and diseases, whereas abiotic are non-living disturbances caused by weather or wildfires. Declines and pest complexes are generally a combination of both biotic and abiotic factors.

Biotic disturbances

Western balsam bark beetle

  • A recently new bark beetle to Yukon sub-alpine fir forests with northern spread and expansion occurring over the last 20 years.
  • Areas infested in FHZ 1 in 2010 have expanded significantly in the last seven years.
  • Endemic populations can cause single tree mortality; however, outbreak populations can cause extensive group tree or stand-level mortality over successive years of attack.
  • Retained red foliage for up to five years, making it difficult to determine trends.

 

Typical signature of western balsam bark beetle, e.g., scattered spots of red trees, in Southeast Yukon.

 

Eastern spruce budworm

  • A small amount of spruce defoliation by eastern spruce budworm was recorded in areas previously defoliated by this cyclical pest in Southeast Yukon and the LaBiche River area. The last known outbreak in this area was from the mid-1990s to early 2000s.

 

Moderate eastern spruce budworm defoliation on hillsides near Pool Creek, west of Beaver River, in Southeast Yukon.

 

Aspen serpentine leafminer

  • The area infested by aspen leafminer was highly variable, with increases in some areas and decreases in others.
  • Ongoing defoliation has been recorded since early 1990s in Yukon aspen stands.
  • In 2017, the area affected by leafminer increased in FHZ 4 from 2010 survey results in the same zone.
  • Very slight decrease in areas infested by aspen leaf miner in FHZ 1 compared to the same area assessed in 2016.

 

Light to moderate aspen serpentine leafminer southwest of Ross River in FHZ 4 along the Robert Campbell Highway and Pelly River.

Large aspen tortrix

  • In FHZ 4, this cyclical defoliator of trembling aspen caused defoliation to over 7,000 hectares near the Yukon/BC border. This defoliator has not been previously recorded in Southeast Yukon. However several outbreaks have recently occurred just to the south in British Columbia.
  • In FHZ 1, the outbreak that began in 2012 is collapsing with only small scattered spots still remaining.
  • Stand-level decline symptoms increased in FHZ 1, and are associated with the severity and longevity of the large aspen tortrix outbreak.

 

Moderate defoliation of hillside trembling aspen by large aspen tortrix, northeast of Tuchitua and west of Hyland River.

Willow leaf miner

  • This common leaf miner was first recorded in Yukon in 2007 adjacent to the Stewart River at Stewart Crossing. In 2017, this defoliator was mapped in both the southern and northern sections of FHZ 4.


Foliar disease

  • Foliar diseases, including rusts, occur on virtually every tree and shrub species in Yukon, with higher incidence generally associated with increases in precipitation.
  • Many foliar diseases require alternate hosts to complete their life cycles.
  • In FHZ 4, both conifer-cottonwood leaf rust and willow leaf rust were recorded, with a higher incidence of the latter in 2017.

 

Stand-level willow leaf rust near Tillei Lake, northeast of Francis Lake (left), and tree-level in Whitehorse (right).

Abiotic disturbances

Winter wind desiccation

  • Commonly referred to as “red belt”, this is thought to result from temperature inversions in late winter and early spring. This is a temporary condition resulting in the loss of some foliage, but trees normally recover quickly.
  • Landscape level damage occurred in higher elevation spruce stands near Moraine Lake and Aishihik Creek in FHZ 1.

 

Winter wind desiccation on white spruce near Moraine Lake in FHZ 1.

Windthrow

  • Shallow rooted tree species, such as spruce, are more prone to windthrow.
  • Small pockets of windthrow occurred in 2017, with the majority occurring east of Pelly Lakes in white spruce.

Flooding

  • High water levels caused damage to riparian zones and forested fluvial areas, with over 238 hectares in FHZ 4 flooding. The largest was southwest of Watson Lake near the BC border at 41 hectares.
  • In FHZ 1, damage due to high water levels was noted on the north side of Pine Lake, and near Aishihik Creek.

 

Dead and dying trees along riparian zones near Aishihik Creek, due to high water levels.

Pest complexes

Wildfire scorching and secondary beetles

  • Tree and basal scorching by wildfire weakens trees such that secondary beetles are capable of overcoming a tree’s resistance.
  • Infested lodgepole pine on the perimeter of wildfires were mapped in Southeast Yukon with the likely causal agent as pine engraver beetle, Ips pini, but other secondary beetles may also be involved.
  • Ground checks in 2010 of similar damage found both pine engraver beetle and another engraver beetle, Ips latidens.

 

Secondary beetle activity in association with the previous year's wildfires, near Coal Creek in FHZ 4.

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.
  • Spatial analysis and ground checks have found a relationship between aspen decline symptoms and frequency and the severity of defoliator outbreaks.
  • Aspen decline is not common in FHZ 4, likely due to the lack of large aspen tortrix outbreaks. In 2017, a total of 62 Ha was affected; an increase from 2010 when a total of 11 ha was identified.
  • In FHZ 1, the area with symptoms of aspen decline doubled to 4,618 hectares, up from 2,380 hectares in 2016. This increase in area is partially due to higher visibility of affected stands in the absence of defoliation, and is indicative of the longevity and severity of the large aspen tortrix outbreak.
  • The largest area with aspen decline along Mendenhall Creek also had the highest levels of cumulative large aspen tortrix feeding damage.

 

Aspen decline adjacent to Mendenhall creek in stands repeatedly defoliated by large aspen tortrix.

 

Thinning aspen crowns likely due to frost damage and defoliation, north of Whitehorse.

 

Animal damage

  • Young lodgepole pine stands were damaged by both porcupines and bears, with the vast majority occurring south of Francis Lake in FHZ 4.
  • Bear damage often causes tree mortality, while porcupine damage generally leads to top or branch kill depending upon the location of the damage.



Table 1: Summary of the comparison of recorded forest health disturbances in FHZ 4 from 2010 and 2017, and only areas within the recent large aspen tortrix outbreak in FHZ 1.

 

Zone 4

Zone 1

 Disturbance Type

2010

2017

2015

2016

2017

 Biotic

 Western Balsam Bark Beetle

607

10,265

-

-

-

 Eastern Spruce Budworm

-

369

-

-

-

 Aspen Leaf Miner

53,085

94,390

-

172

135

 Large Aspen Tortrix

-

7,106

15,690

1,237

452

 Cottonwood Leaf Rust

-

187

-

-

 Willow Leaf Rust

-

1,075

-

-

 Willow Blotch Miner

-

442

-

13

-

 Abiotic

 

 

 

 

 

 Winter wind desiccation

873

-

-

-

1,320

 Windthrow

51

661

-

-

-

 Flooding

506

238

-

-

399

Pest Complexes

 

 

 

 

 

Wildfire scorch and secondary beetles

469

322

-

-

-

Aspen decline

11

62

-

2, 630

4,618

Animal Damage

 

 

 

 

 

 Porcupine

1

18

-

-

-

 Bear

-

46

-

-

-

 

 

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Taking action

 

In addition to the annual aerial survey monitoring of the forest health zones:

  • Proactive management of mountain pine beetle (MPB):
    This marks the eighth 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 BC were very high (within 150 kilometres 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 slowed significant northward movement of MPB populations. FMB continues to monitor the border zone as per our MPB monitoring strategy (See Map 1).

    Since 2009, FMB has been setting up and monitoring 15 pheromone bait tree stations in southern Yukon and northern BC 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 2017.

 

MAP 2: Location of pheromone baiting sites in southern Yukon.

 

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

 

  • 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. As part of proactive management, the spruce beetle risk was assessed by conducting aerial surveys to delineate the blowdown, and ground surveys to determine if spruce beetle is present. In total, 108 ha of spruce-leading and 350 ha of aspen-leading windthrow was mapped; patches ranged from 2 – 25 ha in size. Ground assessments found no evidence of spruce beetle. Only one spruce engraver beetle (Ips pertubatus) was found in the windthrow, as well as wood boring beetles. Access however was hampered by steep slopes, hence not all sites were accessed. FMB will continue to monitor this area in 2018.

 

Ground assessments of white spruce windthrow (left), and windthrow example (right).

 

  • Risk assessment of decked green spruce in Haines Junction:
    Proactive risk assessment of decked green spruce in area with history of spruce bark beetle near Haines Junction.

    Given spruce beetle history and the adjacent hazard, it was recommended that piles be removed. Piles were subsequently burnt and destroyed.

 

Burnt deck of white spruce near Haines Junction; proactive management via risk removal.

 

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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.
  • In 2009, with National Forest Pest Strategy funding, FMB adopted the aerial overview survey program and has been conducting annual aerial surveys since then. FMB has conducted forest health aerial surveys at a landscape level since 2009 to identify both biotic and abiotic disturbances.
  • Aerial overview surveys and ground field checks are a relatively simple and low-cost method for effectively monitoring forest health over large areas (Ciesla, 2000; Mitton and Grant, 1980). Aerial overview surveys are also adequate for regional and provincial summaries and to meet national requirements for the Forest Health Network (BC Ministry of Forests, Lands and Mines and CFS, 2000).
  • As a result, aerial overview surveys are the primary tool for monitoring forest health in Yukon. The forest health aerial overview survey standards used by the BC Ministry of Forests, Lands and Natural Resource Operations are also used in Yukon, which ensures continuity across shared boundaries. Field checks are important for validating the data collected from the aerial surveys. Researchers check a portion of surveyed areas to confirm the identity and severity of the pest or disease disturbance.
  • 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 8 kilometre gridlines to 12 kilometre 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, as well as evaluate the potential risk from various insect pests.

 

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References


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