Mer Bleue, Part I: Ecology

Pink Lady’s Slipper

One place I wanted to take my mother and stepfather but didn’t have time was Mer Bleue, the second largest domed bog in southern Ontario and one of the most beautiful and unique parts of the city’s Greenbelt. Featuring a northern ecosystem more typical of the Arctic than the Ottawa Valley, the Mer Bleue bog is the only wetland in Canada’s Capital Region internationally recognized under the Ramsar Convention on Wetlands.

Sphagnum moss, also known as peat moss, forms the heart of the 3,500-hectare bog. This plant thrives in the cool, acidic, oxygen- and nutrient-poor conditions that characterize northern bogs. When it decomposes, it forms layer upon layer of dead organic matter (called peat), the bog substrate. Because the sphagnum moss tends to grow fastest in the center of the bog, the peat accumulates below and the water table rises. The high water table allows wetland plants to keep growing and for peat to accumulate, increasing the size of the dome over thousands of years. The Mer Bleue bog is about six metres thick in the center of the dome and has taken thousands of years to develop.

Because of the domed shape, the sphagnum bog drains in all directions and most of the minerals found in the bog are obtained from rainwater. This creates a low pH, low-nutrient environment that few plants are able to tolerate. A low-lying mat of vegetation (often referred to as heath vegetation) grows on top of the bog; some of the plant species found here include Labrador tea, Leatherleaf, small cranberry, bog laurel, sheep laurel, cotton grasses, sedges and other plants. Nine species of orchids and carnivorous plants such as sundews and pitcher plants are found in Mer Bleue. Towering over the heath vegetation are the few trees able to survive in bog conditions: Black Spruce, tamarack trees, Trembling Aspen, and birch trees. While the bog may not be able to support much plant diversity, the species that thrive here are not commonly found in other ecosystems and make a visit to the bog worthwhile. This bog ecosystem, in turn, provides habitat for wildlife that are not typically found anywhere else.

I visited the bog on the last Saturday in May, arriving at 8:30 in the morning to take advantage of the quiet time before the crowds arrived. As soon as I got out of the car I startled a Snowshoe Hare feeding in the grass. It bounded across the parking lot, stopped for a moment, then disappeared into the shrubs.

Snowshoe Hare

It was already quite warm and a number of dragonflies were in flight. I decided to walk through the grassy area adjacent to the parking lot to see what insects I could find. Four-spotted Skimmers were numerous, and I came across a couple of Silvery Blues.

Silvery Blue

The abundance of insects probably made for some happy flycatchers; I spotted two Eastern Kingbirds in a tree and heard an Eastern Phoebe calling nearby.

Eastern Kingbird

As I passed by the picnic shelter I heard an Ovenbird and an Eastern Wood-pewee singing in the woods. From there I descended the boardwalk into the marsh; as is typical with most bogs, a wet zone, called a lagg, surrounds the edge of the bog. This transition zone receives run-off from the bog and helps to maintain the bog’s water level. In the case of Mer Bleue, the transition zone consists of a cattail marsh which is home to many typical wetland species such as Red-winged Blackbirds, Swamp Sparrows and Common Yellowthroats.

Mer Bleue Boardwalk

While walking along the boardwalk I heard a couple of other species singing: a Hermit Thrush in the woods, a Veery in the clump of conifers beyond the first bend of the boardwalk, and an Alder Flycatcher somewhere in the distance. Dragonflies were abundant here as well, especially Four-spotted Skimmers and Dot-tailed Whitefaces.

Four-spotted Skimmer

I noticed movement in the water and spotted this Painted Turtle poking his head up through the pond vegetation. He didn’t immediately dive to the bottom of the marsh the way most turtles do whenever a human comes in close proximity.

Painted Turtle

The transition from cattail marsh to bog is abrupt and stunningly beautiful. Here you can see a couple of birch trees growing next to the boardwalk and the low-lying heath vegetation that covers the bog.

Mer Bleue Bog

There were lots of white flowers in bloom throughout the bog. Labrador Tea is a low evergreen shrub which often grows in dense colonies. It bears numerous small, aromatic flowers in a loose, umbrella-like cluster. Each flower has five to seven stamens that extend beyond the petals, giving the flower cluster a fuzzy appearance. Found in peatlands, tundra, moist coniferous woods, swamps, and bogs, Labrador Tea is an indicator of wet, acidic and nutrient-poor organic soils. Because its rhizomes are found deep in a wet, organic layer, it can generally survive fire, and is one of the first plants to recolonize after fire.

Labrador Tea

I was delighted when I came across my first Pink Lady’s Slipper growing right next to the boardwalk. Like most other orchids, Pink Lady’s Slippers require the aid of a symbiotic fungus in the soil in order to survive and reproduce. The fungus not only helps to break open the seed, but also provides the seed with nutrients until the orchid has grown old enough and large enough to produce its own nutrients. At that point the fungus will then extract nutrients from the orchid roots. This mutually beneficial relationship is typical of almost all orchid species.

Although Pink Lady’s Slippers can live twenty years or more, it takes many years to for the seed to develop into a mature plant. Accordingly, picking even one or two of these flowers can have a detrimental effect on the population. This orchid is disappearing in the wild in Ontario because of habitat loss, human disturbance, and misguided attempts to transplant it.

Pink Lady’s Slipper

At that point I had reached the southern-most section of the boardwalk. This is where the most sought-after bog fauna are typically found, and as such I spent most of my morning along this stretch. More photos are forthcoming; stay tuned for Part II!