Spruce-lichen forest (Photo:  Susan Beaumont, WRRB) Spruce-lichen forest (Photo: Susan Beaumont, WRRB)

Impacts of Wildfire Extent and Severity on Caribou Habitat Research Project Update

Wildfire is part of the boreal forest ecosystem and the natural life cycle of the forest.  It helps the forest renew itself by releasing valuable nutrients stored in the litter on the forest floor and opening the forest canopy to sunlight, stimulating new growth.  In turn, these changes in vegetation often affect the movement of wildlife populations whose need for food and cover means they may need to relocate as the forest patterns change. 

While fires are natural events in the boreal forest, they have increased in number and intensity in recent years, likely due to climate change effects including warming temperatures and altered precipitation (falling snow and rain) patterns, and this trend is expected to continue.  With these changing fire “regimes”, larger areas may be burned in future, with less old-growth forest and fewer older trees –and lichens—remaining.  Ground lichens are an important food source in winter for caribou.  Traditional knowledge and science information suggest that both ɂekwǫ̀ (barren-ground caribou) and tǫdzı (boreal caribou) avoid recently burned areas.  This could be because there is less food for caribou after a recent fire, but the lack of cover from predators and other factors may also play a role. 

Several important questions arise from these observations. What are the effects of fire disturbances on caribou habitat? How do different areas respond to different degrees of fire?  What is the potential role of a changing fire regime on winter habitat for caribou?

Landscape view of one of the 2014 fire scars. Burn site is located between Behchokǫ̀ and Fort Providence, NT. Photo credit: Kirsten Reid.

How does fire severity affect forest recovery in the NWT?

Does the severity of a forest fire (how deeply it burns and how much of the canopy it burns) change how forests here in the NWT recover after a fire?  Plant communities grow again after fire, but it’s not known how long this takes or how long it takes for key habitat resources like lichen to recover in the NWT.  To complicate matters, burned areas don’t necessarily come back the way they were before.  Studies in Alaska and other locations show that Black spruce – lichen forest, for example, sometimes regenerates to tundra-like vegetation or to deciduous forest with species such as birch, poplar, and willow, where lichen doesn’t grow.  How often this happens or whether it happens in the NWT is unknown.   

Because knowledge is incomplete, predicting how much caribou habitat there will be in the future, or where it might be found is difficult.  A better understanding of how today’s wildfires are affecting the make-up of caribou’s forest habitat will be valuable in managing wildlife and habitat in relation to fires and other disturbances. 

Quadrat showing lichen sampling plot in a site where there has been no fire since before 1960. Photo credit: Nicola Day.

Research Update

A three-year research and monitoring project that began in 2015 involves field studies to address some of these gaps in knowledge.  Jennifer Baltzer, Associate Professor of Biology and Canada Research Chair in Forest and Global Change at Wilfrid Laurier University, who’s heading up the project, presented an update on the 2015 and 2016 field seasons at the CIMP research results workshop in Behchokǫ̀ on January 31-February 1, 2017. 

She described how the research team established a network of 230 permanent sample plots in the Dehcho and Tłı̨chǫ regions in areas that were affected by the extreme fires of the summer of 2014, the largest fire season on record.  The team measured fire severity (the depth of burn and canopy consumption), the recovery of vegetation and the establishment of tree seedlings to assess the impact of the 2014 fires. Information collected from the sample plots help researchers understand the path that forest regeneration has been taking since the 2014 fires.  Boreal fire regimes are changing.  Does the “fire regime”, the pattern in which fires naturally occur in a particular ecosystem, impact what tree species are coming back?

Resprouting Betula glandulosa (dwarf birch) two growing seasons post-fire. Photo credit: Alison White

Black spruce and jack pine trees store large numbers of wax covered cones in their canopy that open up from the heat of the fire, releasing their seeds onto the freshly burned seed bed. As a consequence, these forest types are often “self-replacing” (they replace themselves after fire). However, when fire is severe and either the moss layer of the soil is burned away (exposing mineral soil) or the cones in the canopy are burned badly (limiting spruce and pine seed availability), other species like trembling aspen and white birch may be able to establish. Aspen and birch can regrow quickly from stumps and roots of burned trees.  They can also recolonize burned sites by producing abundant seeds that can be blown long distances by wind.  Evidence from Alaska suggests that these alternate successional “trajectories” or pathways are more likely and also more frequent because of increased burning.  Monitoring the sample sites will allow the researchers to see if this is the case. 

Researchers are also looking into how fast forests are returning and in particular, how quickly caribou forage (food) is coming back.  In the 2015 field season, the crew set up quadrats—small 1-metre square plots—to see which species were recovering after the fire and to measure the composition of the vegetation community.  They also noted their density –i.e. whether there were many plants in an area or only a few, scattered ones. The research team also observed how these plants were growing back, whether by resprouting from underground roots undamaged by fire, for example, or regenerating from seed.

Vegetation quadrat showing regenerating vascular plants in the second growing season post-fire. Photo credit: Alison White

The researchers returned to the same sites in the 2016 field season to see how many plants survived in the stressful growing environment that is left behind by a forest fire.  They will also set up additional vegetation plots on the Taiga Shield varying in time since the last fire and visit older, historic burn sites from large fire years (e.g., 1994/95 and 1979/80) as well as forests with no fire record (those that burned before the 1960s) to look at forest recovery.  By visiting those sites, the team will be able to observe what vegetation is recovered after 20-40 years and look at the rate of recovery of forage and forest cover.  They use tree rings to measure how long it has been since a site last burned.

Landscape view of one of the 2014 fire scars. Burn site is located between Behchokǫ̀ and Fort Providence, NT. Photo credit: Kirsten Reid.

What have they learned so far?

Timing of fires and degree of canopy consumption affect tree regeneration.

Results from the study so far are preliminary, but researchers made a number of observations.  They found that wetter sites have a higher canopy consumption than drier sites.  In other words, where the forest was wetter, fire burned more of the upper layer of the forest formed by the crowns of mature trees. The wetter sites were dominated by black spruce which tend to grow closer together than jack pine and retain lots of dead, lichen covered branches along their stems (ladder fuels), which act as fuel during fires; in contrast, the drier sites were more open jack pine stands which tend to have clearer tree stems. The degree of canopy consumption affected seed rain; where cones were badly burned or completely consumed, seed rain for black spruce was much lower, reducing potential for black spruce regeneration at these sites.

The researchers also found that neither tree seedling establishment nor ground vegetation recovery was impacted by the severity of the fire in terms of consumption of the peat soils. This is in contrast to results from Alaska, where deeper burning led to increased frequency of poplar regeneration in formerly black spruce stands and reduction in the ground vegetation resprouting following fire. This may be in part because the depth of burning in the NWT fires was not as extreme as that observed in Alaska and these researchers are investigating why that might be the case.

While there is no evidence for a shift toward deciduous species (e.g. poplar and birch), jack pine establishment was very high, and there is evidence of a shift away from black spruce dominance toward jack pine dominance, even in stands where black spruce was the dominant species prior to fire. High rates of jack pine recruitment were particularly evident where fires burned later in the season, which was an unusual feature of the 2014 fires. Jack pine is a very fast-growing, competitive conifer, and its presence in the NWT (it is absent in Alaska) seems to contribute to different post-fire regeneration patterns than have been shown elsewhere.

Dense bed of jack pine seedlings in a 2-year old burn (Photo credit: Kirsten Reid)

More research, monitoring, and discussion will be needed to add to a developing picture of how forest habitat is affected by the size and severity of forest fires—and the potential implications for caribou. 

What is planned for the coming field seasons?

During 2017, the team is continuing to sample in older stands with variable age since last fire in order to develop the relationships between stand age and forest structure, composition, and ground vegetation conditions. Part of this work involved measuring how much (biomass) lichen is present at each site so we can understand the rates of recovery of this important winter food resource. The types and abundance of all ground vegetation are measured, and analyses will include the assessment of the abundance of plants that serve as food resources for different wildlife species, including caribou.

Geneviève Degré-Timmons sampling lichen to allow for estimation of biomass. Understanding the biomass of lichen is important for predicting how much forage is available for caribou. Photo Credit: Nicola Day.

Using this information

The boreal forest is a huge area, and it would be impossible to monitor every part of it.  But the information gathered from the sample sites can be used to develop good landscape models that can help researchers predict changes under different climate and fire scenarios. For example, if climate changes in a particular way, or if large fire years become more frequent, what will habitat look like for caribou and other wildlife?  How much habitat will be available for these species?  Being able to answer questions like this will help managers make better informed decisions about land use and ensure that appropriate habitat is available in future to support wildlife populations.  Baltzer’s team is working with scientists from the Canadian Forest Service and Laval University to do just this for the NWT.

Fact Box

  • A fire regime is the pattern, frequency, and intensity of wildfire that prevails in an area over long periods of time.  It includes characteristics such as type of fire the extent (size) of fire, the severity of burning, and the seasonality (the period of time during the year that fires typically burn in an area). 
  • Fire regimes can change with topography (the surface features of land such as hills and creeks), climate, and the fuel that is available for fire to consume (e.g. leaf litter on the forest floor)
  • The intensity of wildfire is the amount of heat released over time.  The severity of a fire is how much of the forest vegetation and organic soil is consumed –the depth of the burn.