"It’s Not Easy Being Green..."

Heather Stewart
Ecosystem Scientist, Wapusk National Park

Colourful flowers along the bank of the Owl River Colourful flowers along the bank of the Owl River. Not all of the park’s flowering plants are small ground-hugging species, and many colourful blooms can be seen in areas of the park other than the beach ridges. Wapusk NP, in the right season, can have carpets of showy flowers covering the gravel banks of the Owl and Broad Rivers. Most of the plants in this photograph, such as broad-leaved willowherb (Epilobium latifolium), northern hedysarum (Hedysarum mackenzii), alpine arnica (Arnica alpina) and alpine goldenrod (Solidago multiradiata), are usually found north of Churchill.
© Parks Canada

The area in and around Wapusk National Park (NP) is recognized around the world for its significant biological diversity. The park protects important habitats and populations of polar bears, birds and plants. Wapusk NP also contains some of the youngest land in Canada, as a result of the retreating Hudson Bay shoreline in response to isostatic rebound – the rising of the land following the glacial period.

But if you think that all of this points to a cushy life for plants, you’d be mistaken. In Wapusk NP, it’s not so easy being green... Plants growing along the Hudson Bay coastline, and for a considerable distance inland, are rooted in shallow soil underlain by permafrost. Here, they are exposed to north-easterly storms and are subject to abrasion from ice crystals driven by winds sweeping across a treeless terrain where the mean annual air temperature is -3.5° C. And, conditions are not much friendlier to plants growing farther inland. Here, although they are more sheltered, plants must grow in peat bogs that are acidic, low in nutrients and poorly drained due to the permafrost below the surface which holds water on the low-lying landscape. Despite these challenging conditions, or possibly because of them, many noteworthy species occur within the park, making it a very special place to see plants.

So, given these unique habitats, how many plant species are found in Wapusk NP? The current tally of plants (excluding mosses and lichens) is approximately 370 confirmed species. This inventory is the combined result of work completed by University of Manitoba Botany inventory (2002-2008), the ParkSPACE Terrestrial Ecosystem Mapping (TEM) project (2009-2010) and the work of individual researchers (multi-year projects since 1996).

Terrestrial Ecosystem Map of Wapusk National Park Terrestrial Ecosystem Map of Wapusk National Park
© Parks Canada

This Terrestrial Ecosystem Map of Wapusk National Park was created using satellite data.

The plant species found in Wapusk NP are spread over three broad ecological zones – the Sub-Arctic Woodland, Boreal Forest and Arctic Tundra Bioclimatic Zones. Most of the plants in the park, about 52%, have subarctic affinity. Boreal/temperate plants make up about 38%, and the remaining 10% are arctic species.

Satellite images of Wapusk NP show stunningly complex patterns in the landscape. What do these patterns look like at ground level?

Moving inland from the Hudson Bay coast (diagram - cross section) there is a gradient in wetland type. Nearer to the coast are fens which are rich in nutrients and connected to mineral soils.

Farther inland are peat polygon bogs (the type of bog most common over permafrost) which are poor in nutrients, most of which come from precipitation.

Away from the coast, the landscape becomes a mosaic of dry hummocks, thaw ponds, meltwater ponds and fens. The plant communities are dry and dominated by lichens on the peat hummocks, but wet and acidic in the hollows.

Satellite images of Wapusk NP Satellite images of Wapusk NP
© Parks Canada

Some of Wapusk’s flowering plants... up close.

Mountain avens Mountain avens
© Parks Canada

Mountain avens

On beach ridges along the coast, low growing white mountain avens (Dryas integrifolia) is the “pioneer species” – the first to be able to gain a foothold on the open ground. Its low, woody mats of foliage trap, seeds and organic material. This plant is commonly found further north, growing on dry tundra, but here in the park it is restricted to a narrow band along the coast. It does not grow well further inland because it is shade intolerant and is crowded out by shrubs.

Prickly saxifrage Prickly saxifrage
© Parks Canada

Prickly saxifrage

Another common plant on the beach ridges is the prickly saxifrage (Saxifraga tricuspidata). In some places this densely matted saxifrage is as common as mountain avens. These plants thrive on exposed, gravelly areas with basic pH.

Lepage wild flax Lepage wild flax
© Parks Canada

Lepage wild flax

One of the park’s more rare plants, lepage wild flax (Linum lewisii var lepagei), is irregularly found right at the coast at the high tide mark, growing among sea lyme grass (Leymus mollis). This plant is one of only a few species which arrived in Canada after the last ice age.

Purple saxifrage Purple saxifrage
© Parks Canada

Purple saxifrage

Purple saxifrage (Saxifraga oppositifolia) is a true harbinger of spring. It flowers as soon as the snow begins to melt, often between snow patches. Without the large showy cushions of bright purple flowers, these plants are often overlooked later in the season (they seem like dead patches of scaly leaves) but they carpet the beach ridges with vibrant colour in June.

Small butterwort Small butterwort
© Parks Canada

Small butterwort

A very small insect-trapping plant called small butterwort (Pinguicula villosa) is a northern species frequently found along treeline wetlands in the park. Given its small size, this butterwort is often overlooked, but during flowering season, the small bright purple flowers are easy to spot. Its buttery leaves, which trap insects, are well hidden beneath the mosses. After the flower is past, only the single stalk, like a toothpick, remains visible.

The diversity and complexity of habitats, the weather conditions and the rebounding shoreline ridges truly make Wapusk NP a fascinating place to see flowering plants, including many which are usually found farther north.

It may not be easy being green here, but that makes it all the more fascinating!