Impacts of Wildfire Extent and Severity on Caribou Habitat: From Woodland to Barren Ground

With large wildfire events appearing to become more frequent and more intense in the NWT, questions are emerging about how the fires are affecting wildlife habitat –and wildlife.  In particular, what effects are fire disturbances having on caribou habitat?  How do different areas respond to different degrees of fire?

It’s a complex question.  The boreal forests of Wek’èezhìı and other parts of the NWT are important caribou habitat –year round homes for Tǫdzı (Boreal caribou) and wintering grounds for ɁEkwǫ̀ (Barrenground caribou) where caribou can forage for lichen and other vegetation they depend on.  Those forests are intricate, dynamic ecosystems –each a complete system made up of many elements starting with its ground floor.  Soil, temperature, permafrost, ground cover, organic soil thickness, and the mineral soil beneath it, are all integral parts in addition to forest trees and plants.  Soil is the medium for vegetation growth –any changes to the soil will affect the vegetation community in some way.  Similarly, changes to the forest cover, such as when trees are consumed by forest fire, will affect other parts of the ecosystem, including the soil. 

Severe 2014 wildfire burn site on Highway 3 (Photo: Xanthe Walker, University of Saskatchewan)

Pulling together researchers from different disciplines is an approach that can contribute to a more complete picture of what’s happening to forests in burn areas.  Dr. Jennifer Baltzer, Associate Professor of Biology and Canada Research Chair in Forest and Global Change at Wilfrid Laurier University, is leading an interdisciplinary research team that is studying the impacts of wildfire on tǫdzı and Ɂekwǫ̀ caribou habitat. Permafrost, soil and vegetation scientists are all part of the team.  This 3-year project is a collaboration with many different partners, including University of Saskatchewan which is working on a similar project in Saskatchewan. The project is also complementary in nature to a Tłı̨chǫ Knowledge project that the WRRB is undertaking entitled When Do Caribou Return? Impacts of Wildfire on Tǫdzı (Boreal caribou) [Read story here]

What prompted Dr. Baltzer to head the study?  There’s a personal interest:  she and her family spent last summer in Yellowknife and experienced first-hand the fires and smoke from the extreme forest fire season of 2014.  And there’s a professional interest that comes from her research program focused on the impacts of climate warming on ecosystems across Canada's North, including the thawing of permafrost and resulting changes to the vegetation community in the boreal forest.  Specifically, how do changing permafrost conditions affect the productivity and structure of vegetation communities in the boreal forest?

Forest fires, Dr. Baltzer explains, add an extra element to these changes in the boreal forest.  She is interested in how permafrost conditions and fire severity interact to determine how the forest will recover.  How does fire severity (how much of the forest biomass and organic soil is consumed)–affect how plants regenerate and how quickly they come back, and is that a function of permafrost conditions?  Does the forest recover the same after fire, or is more severe fire altering which plants return to the system? The rates and direction of forest recovery following fire determine which wildlife will use the land and when. 

The focus for this first year of the project is to sample sites burned in the 2014 fires.  "The longer you wait after a fire," Dr. Baltzer explains "the more information is lost."  Next year, the team will do their sampling in older burn sites to look at forest recovery.  For that phase of the project, they will look at studies of historic burn areas, such as the work done near the East Arm of Great Slave Lake after the 1979-1980 fires and Dr. Suzanne Carrière’s monitoring work in the Tibbett Lake area over the past 10 years.  Dr. Carrière, Wildlife Biologist (Biodiversity), Government of the Northwest Territories, studied forest recovery and shrub regrowth after the Tibbet Lake fire in July, 1998.  By visiting those sites, this team will see what’s recovering after 20-40 years and look at the rate of recovery of forage and forest cover. 

Dr. Baltzer also referred to studies in Alaska where wildfire has been shown to change the forest.  How are nutrients and carbon stocks in the soil affected by fire? In the boreal forest, carbon and nutrients are stored in the thick organic layer on the forest floor. Severe fires –fires that burn longer and hotter--can burn off the peat –the organic matter at the soil’s surface.  “Poplars do well in that environment," Dr. Baltzer explains, “but spruce trees don’t.  We’re interested in seeing whether the same things are happening in the NWT.  And with those changes to the forest composition, what changes are there in the wildlife?  Which species use that new forest?"

Sampling sites were selected to represent important gradients including pre-fire forest composition (e.g. spruce v.s. pine), time since last fire (historic fire records are available back to 1960), and the time that the burn occurred (early v.s. late summer).  Geographically, the study area focuses on sampling sites in the Taiga Plains and the Taiga Shield, two prominent “ecozones” in Wek’èezhìı and in the NWT.  The low-lying lands of the Taiga Plains cover most of the western NWT, with the forests, lakes and wetlands of the Taiga Shield to the east.  Last summer’s wildfires were extensive, covering a huge swath of land extending across these two ecozones right up to the tree line.  The research team established a network of study sites in an approximately 250 km radius around Yellowknife, where fires have affected a wide range of ecosystem types. 

Aerial photo of a 2014 forest fire burn site near the Discovery Mine / Lucky Lake area in Taiga Shield ecozone  (Photo: Xanthe Walker, University of Saskatchewan)

The Taiga Plains sampling sites were the easier of the two to access.  There were sites accessible by road in the Kakisa and Fort Providence areas, for example, and two big burn areas along Highway 3 near Behchokǫ̀.  In the Taiga Shield, field crews could boat to and walk into sites near Gamètì and Wekweètì, while floatplane and helipcopter access was required for the Discovery Mine / Lucky Lake area northeast of Yellowknife. Community support has been critical for the project, including logistics coordination and support, guides' tremendous knowledge of the area, and generous access to cabins for home bases for the crews.

What are some of the research activities that have taken place so far?

Three field crews were out in June, July and August: two vegetation and soils crews and a permafrost crew.  They set up transects at the various sampling sites to make a number of observations.  What kind of plants were there and how were they growing back (e.g. resprouting vs. regeneration from seed)? What was the pre-fire forest structure and biomass at the site?   How severely burned was the area?  What parts of the trees were burned?  Were the cones burned, for instance, which would limit tree seed input to the site following fire?   Have the trees fallen or are they still standing? Fallen trees act as obstacles to wildlife. 

In the boreal forest, organic soil, lichens and feather moss grow on top of mineral soils.  If there is a light forest fire, not much of this organic layer is lost.  But a severe fire can burn right down to the nutrient-rich mineral soil, which alters which tree species will regenerate successfully.   Researchers can actually measure how much organic soil has been lost by clues in the tree stems. Black spruce produce tiny roots at the surface of the peat soils; scars of these roots remain following fire allowing for direct measurement of how much peat was lost during the fire. 

The soil crew also dug pits to look at the soil profiles (how thick were different soil layers) and collected samples for laboratory analysis. The researchers will look at how much carbon was lost from the soils during fire and how soil nutrients change with fire. 

The vegetation crew set up quadrats –small 1 metre square plots--to measure the composition of the vegetation community.  Which species are  recovering after the fire?  What is their “density” –are there many plants in an area or only a few, scattered ones?  The same sites will be monitored next year to see how many plants survived in the stressful growing environment that is left behind by a forest fire. 

Field crews at work at a vegetation quadrat marking location of seedlings (Photo: Xanthe Walker, University of Saskatchewan)

The permafrost crew set up transects to map permafrost using geophysical methods and see how deep the active layer is, the surface layer that thaws in the summer and freezes in winter, and how deep the permafrost layer below it is.  The team is interested in how these conditions change following fire and whether permafrost is lost from some systems entirely.  For example, in peatlands, where permafrost is protected by the vegetation and the thick organic soils, fire may drive the loss of permafrost. Without the shade from trees and plants and insulation from the thick peat, the ground  temperature can increase dramatically.  The research team wants to find out whether there is a loss of permafrost and how that impacts plant recovery and loss of carbon from the system following fire.  The crew also drilled holes at some sites to install temperature sensors that were coupled with snow depth sensors, and small weather stations so they can see how energy inputs to the site and consequently permafrost temperature changes over time following fire. 

Frost probing and ground soil measurements to understand permafrost changes post-fire (Photo:  Xanthe Walker, University of Saskatchewan)

What happens next?

The research team is busy entering its data from this summer’s field work and analyzing samples in the lab.  They hope to have preliminary results this winter. 

Next summer’s field work will start up again in May 2016, revisiting this year’s sampling sites, setting up additional vegetation plots on the Taiga Shield, and visiting historic burn areas. 

The boreal forest is a huge area.  One of the outcomes for this project is scaling up the field-based measures to develop good landscape models that will 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?  This uncertainty makes land use planning very difficult, and a tool like this will facilitate good management decisions.

Fact Box

• Fire is not new to the boreal forest and plays a key role in maintaining healthy boreal forests, renewing them; opening up the forest floor giving seeds space to germinate and seedlings to grow; and, depending on its severity, releasing nutrients making them available for new plant growth. 
• How do plants grow again after a forest fire? 
  • Some have below ground root systems that store sugar and nutrients and can send up new sprouts, resulting in a quick recolonization of the area. 
  • Some will grow new leaves or needles.
  • Others, like Jack Pine and Black Spruce, have fire resistant seeds that will sprout following a fire. 
  • Or seeds can come into a burn site from elsewhere:  birch and aspen produce thousands of wind-borne seeds in neighbouring unburned stands and these stands are often the first trees to grow in a burned area. 
  • Many species of moss can sprout from spores dispersed by wind.  These species help other species to establish by accumulating organic material like leaves and twigs, and by holding moisture. 
• After a fire, regeneration of the forest often follows a general pattern of  succession, starting with soil building and early colonization by mosses, wildflowers and grasses, then deciduous shrubs and trees, and finally by conifers.  However, there are many environmental factors that can make the path succession takes different in different situations.