The transition between forest and tundra in arctic regions – referred to as the forest-tundra ecotone and punctuated by the limit of tree growth, known as treeline – is expected to undergo extensive change as a result of continued climate warming. However, sparse empirical data on recent treeline dynamics in many northern regions has left considerable uncertainty about the rate, extent, and mechanisms of such change. Moreover, there is a conspicuous absence of field studies from north-central Canada, presumably because it is remote and difficult to access. In addition to ongoing climate change, this part of Canada has experienced significant land use change associated with mineral exploration and development, widespread forest fires, and rapid decline of migratory caribou herds in the last two decades.

We spent four weeks traversing the forest-tundra ecotone in Canada’s Northwest Territories by canoe in July and August 2016. The four of us, along with all gear and scientific equipment, flew from the city of Yellowknife by float plane to a lake north of the treeline. We paddled 200 km south to the small community of Wekweètì located at the northern edge of the boreal forest. Several investigations were conducted en-route, each aimed at documenting the patterns and processes associated with contemporary vegetation dynamics in this region. Thirteen base camps were established along the transect and daily sampling excursions were made from each camp.

Yellowknife is a city of approximately 20,000 people located on the shore of Great Slave Lake. The area has been home to the Dene people for centuries, but the origins of the modern city began with the rapid growth of gold mining in the 1930s. Yellowknife has since become the capital and economic center of the Territory and is connected to the rest of Canada by an all-season highway and numerous daily commercial flights.

Our flight north from Yellowknife crossed the Taiga Shield ecoregion, a vast area of northern boreal forest situated on Precambrian bedrock. The region contains thousands of lakes of various sizes and bedrock outcrops are common. Mean annual temperature ranges from -4 to -9°C and mean annual precipitation is between 250 and 400 mm, 40% of which falls as snow. The distribution of vegetation is strongly influenced by this physical template, and forests are constrained to lower slopes and bedrock depressions where suitable soils exist.

Our drop-off point was Big Lake, 275 km north of Yellowknife at the head of a watershed that drains southward into the north arm of Great Slave Lake. After an hour-long flight, we were left alone with all of our equipment and supplies and saw no one else for four weeks.

With no roads but an abundance of lakes, boats are the best mode of travel across the landscape. We used two 17-foot collapsible canoes built from a reinforced PVC exterior held under tension by a frame of tubular aluminum. They pack up into a large dufflebag and can be assembled in less than 30 minutes. This time-lapse video clip shows the process of building the boats on our first day.

Increases in satellite measures of vegetation productivity have been observed at high northern latitudes over the past several decades; a phenomenon known as ‘Arctic greening’. In many regions of the Canadian Arctic, greening has been linked to increases in the growth and abundance of deciduous shrubs, like the dwarf resin birch (Betula glandulosa) seen here forming thick, low-growing mats.

We measured the extent of greening in the region using a time-series of Landsat satellite images spanning from 1984 to 2016. To support this, we established field plots at 34 locations along our route. Measurement of vegetation in each plot provided the data necessary to calibrate our satellite imagery; a process referred to as “ground-truthing”.

Conifers growing at their northernmost limits, like this white spruce (Picea glauca), frequently occur in dense, low-growing mats. These individuals grow slowly as a result of cold temperatures and show signs of regular damage as a result of exposure to high winds and blowing snow.

The region is the traditional homeland of the Tłı̨chǫ First Nation. Dogrib Rock (Ɂenàts'ıį̀k̨wì), seen here on the horizon, is visible from great distances in many directions and has been used as a navigational landmark for generations.

Our campsites consisted of two all-season personal tents for sleeping, and a larger communal tent for cooking and eating. Meals were all prepared in advance, dehydrated, and packed into watertight barrels. We used naphtha stoves for cooking, but supplemented this with wood as we travelled south into forested areas.

Despite its name, the northern treeline is not an abrupt boundary. Instead, it is a zone of transition from continuous forest to treeless tundra comprised of increasingly smaller patches of trees separated by increasingly larger patches of shrubs and tundra.

We measured and sampled nearly 500 spruce trees. Three-quarters of all trees were black spruce (Picea mariana). White spruce (P. glauca) increased in abundance as we travelled south, but was limited to dry, well-drained, sites. The average year of establishment was 1918, but ranged from 1767 to 1992. All of the patches contained trees older than 100 years but most were small in stature. The average height of black spruce was just 2.2 meters, and the average diameter at breast height was just 3.4 cm. Ring-width analysis indicated that spruce growth has increased significantly over the last century.

Surveys of spruce seedlings were conducted to provide data on establishment patterns. We set up plots around seedlings to collect data on the microenvironment they were growing in and compared that with data we collected from random locations where seedlings were not present. Seedlings showed a clear tendency to be found in areas with enough shrub cover to protect them from wind, but not too much that shading and competition would inhibit their growth.

We brought two 20-watt solar panels for charging essential field electronics like cameras, GPS receivers, and a laptop computer. But the power requirements for a drone were just too much for our solar array. Instead, we used a parafoil kite to hoist a camera and take aerial photographs of our field sites.

The photos from the kite camera reveal the mosaic of plant types that comprise the treeline ecotone. Trees, shrubs, and low-growing ground vegetation are the various shades of green in this image. Rocks, bare ground, and lichen are represented by the much lighter grays. Scale of the image is indicated by the person in the left of the image (in blue).

On day 22 we arrived at Winter Lake (Beɂaitì), pictured here. Winter Lake narrows into the Snare River at its western end. This is the former location of Fort Enterprise, established in 1820 by Captain John Franklin during the ill-fated Coppermine Expedition to the Arctic coast. Eleven of Franklin’s 19 men died during the expedition. The fort has long since disappeared, but its position along our route was a reminder of the potential dangers of remote wilderness travel.

Mosquitos and blackflies are abundant everywhere in northern Canada. Frequent application of repellent was necessary, and we often wore nets and special ‘bug jackets’ to prevent them from getting under our clothing. Breezes temporarily reduced their numbers and provided a welcome break!

A Government of Canada geological survey team travelled a portion of our route in 1932. They took several photos that we re-photographed for the purpose of documenting landscape change. This photographic pair, taken on top of an esker (a long winding ridge of sand and gravel), shows the extent of forest growth that has occurred in the 80+ years since.

This second pair of photographs further illustrates vegetation change in the area around Winter Lake. Two older trees in each photograph are labelled (A & B) for reference. Someone can be seen running the rapids in a canoe in the earlier photograph. In our recent photograph, the water is markedly lower, although this is partly attributable to seasonality. The early image is from July 7; ours is from August 15.

The rivers between lakes were short and swift. Many were shallow and required us to portage around them or walk the boats through them; but several were traversable. The canoes proved every bit as seaworthy as any hard-sided boat. They are quickly becoming a common type of canoe for remote expeditions in Northern Canada because of their transportability.

Our route fell on the range of the Bathurst caribou herd which historically ranged from the Arctic Ocean to Great Slave Lake. The herd has been an important source of sustenance for generations of Dene and Inuit peoples. However, the population declined from an estimated 349,000 animals in 1996 to just 8,200 animals in 2018, and hunting has ceased. The cause of the decline is not entirely known, but is well outside the historic range of variation. It is telling that we did not see any caribou on our journey; only bones and old antlers.

Fire is a natural occurrence in the boreal forest, but the size, frequency and magnitude of forest fires are changing as climate continues to warm. This photograph was taken from a 275 ha area south of Roundrock Lake that burned in 2004. The abundance of young spruce is indicative of the regenerative capacity of these forests.

After 30 days we reached the community of Wekweètì on Snare Lake. Approximately 130 people, mostly Tłı̨chǫ, live here. Services include a school, general store, health center, and an airport which supports flights to Yellowknife. We spent three days in Wekweètì and were able to meet with community councilors and resource management staff to describe our research and hear first-hand their own observations of environmental change in the region. They expressed strong concern about the caribou population and a potential link with climate change impacts, which led us to develop a follow-up research project to explore the relationship between increased shrub abundance and the herd’s decline.