Massasauga Rattlesnake (Sistrurus catenatus).
Photo: Mark Conboy
A wrong turn on an unfamiliar trail can lead to confusion, frustration and the unenviable job of backtracking across some slippery talus slope or through a knee-deep swamp. On the other hand, it can also lead to a wonderful discovery. By way of example, I took a wrong turn off a Bruce Peninsula trail earlier this month, and I was rewarded for my buffoonery by an encounter with one of Ontario's least often seen and most misunderstood reptiles: the Massasauga Rattlesnake (Sistrurus catenatus). I went to the Bruce Peninsula specifically in search of rattlesnakes and much to my delight what I found was a land full of additional surprises.
The focus of my explorations was Lion's Head Provincial Nature Reserve, the real treasure of the Bruce Peninsula, with one of most dramatic coastlines on the Great Lakes: shinning white cliffs that support ancient forests of stunted Eastern White Cedars (Thuja occidentalis). The cliffs plunge into a band of forest which in turn sweeps down to the crystalline waters Georgian Bay. Upon the cliff tops themselves, the forest, dense with Eastern White Cedar and Balsam Fir (Abies balsamea), hides a geological wonderland of glacial potholes, acid-worn caves, bottomless crags, overhanging rock faces, and erosion-sculpted boulders of ten thousand different forms.
I started on the trail at six o-clock one evening, into a forest alive with the ethereal whistling of Swainson's Thrushes (Catharus ustulatus), which lent the evening air a subdued and angelic texture. I worked my way east along the ridge top from one spectacular lookout to another. To the north I could see the peninsula stretching far off, a vast swath of seemingly undisturbed forest and coastline. Not a breath of sound, not a light, not a tower, not a road, not a cabin betrayed the illusion of vast and insurmountable wilderness. I knew what truly lay out there, hidden by distance, green forest, and heaving geology. Of course I knew of the towns and cottages, the lighthouses, the roads and their stinking cars. But I let my mind imagine a world unsullied by humans, a wild land stretching from Lion's Head to the tip of the peninsula and beyond to Manitoulan Island, to the North Shore, across the boreal hinterlands, to the freezing waters of Hudson Bay. A world teeming with game and fish and winding trails. The cries of a raven brought me back to reality. And so I lifted my pack, and hit the trail once again.
The cliffs upon which I walked dropped down for ninety or one hundred metres into the forest below. Far from smooth, the cliffs were undercut, overhanging ominously, inviting me to stand upon many a narrow slab, as though to dare fate. The cliff faces were pocked by small depressions and shelves, and it was upon those little natural balconies their existed a most remarkable community of ancient trees, a vertical forest of centuries-old Eastern White Cedars. Many of the cedars, though small and spindly, more like shrubs than proper trees, were two, three, four or even eight centuries old. The oldest yet discovered at Lion's Head is over 1,300 years old and for all its age is only about seven metres tall.
Dolostone cliffs at Lion's Head Provincial Nature Reserve with Eastern White Cedars (Thuja occidentalis).
Photo: Mark Conboy
The cliff-side cedars are natural bonsais, sculpted by centuries of extraordinarily slow growth on water- and nutrient-poor dolostone, twisted by driving winds, polished by blowing snow, and cracked by frost. Their trunks and limbs are gnarled, knotted and ropy. They do look truly ancient, truly sage-like. Many of the cedars appear to be half dead, and indeed they are. Eastern White Cedars, perhaps unique among Ontario trees, grow in sections; one portion of the root mass feeds one portion of the crown. In this way the left side of a cedar may die as the roots which feed it run low on nutrients while the right side of the tree continues to thrive, its roots having managed to find sufficient resources. This segmenting, may be one of the reasons why cedars have such staying power, where other less versatile species simply can't survive. Over the past 10,000 years, fire has periodically burned along the cliff tops, but the cliff faces appear to have been spared, and so the trees were allowed to grow old, excessively old. Even that zealous craze for wood and civilization, the rampant forest clearing, left the difficult-to-access vertical forests unmolested. The longevity of the ancient cedar forests it would seem, is a lucky coincidence of topography: safe there on the cliff sides from the ravages of fire and man. But not entirely safe.
Perhaps the single biggest threat that the ancient cedars face todays is rock climbers. The cliffs of Lion's Head are a popular sport climbing destination. It's easy to spot the most well-climbed routes: lichens have been rubbed away, duff has been swept from the tiny ledges, and in some rare cases, cedar branches have been cut. It seems that most of the pruning, and it hasn't been excessive, was done before the agelessness of the cedars was discovered. Though, if a saw-wielding climber had bothered to look at the annual growth rings of the limbs they were pruning it may have been obvious just how old those trees were. Today, the climbing community has more awareness of the ancient trees, and thankfully, disturbance is less of an issue as it was in the past. To share the cliff faces with age-old trees, that can only add to the exhilaration of the climb, can it not?
Cryptoendolithic organisms (not from the Bruce Peninsula in this example) growing inside a rock.
Photo: Guillaume Dargaud (Wikimedia Commons)
Eastern White Cedar belongs to the family Arborvitae, from the Latin, tree (arbor) of life (vitae). Indeed a fitting appellation for this long-lived species. The cedars though are not the only ancient cliff dwellers. The roughly textured dolostone supports an array of lichens, tiny symbiotic organisms that give colour to the cliff faces. Hidden within the pores of the rocks themselves is even more unlikely and more bizarre life, cryptoendolithic organisms. Nine species of cyanobacteria and 13 species of green algae living 1-5 mm deep within the porous rock have been recorded on the Bruce Peninsula. From the right vantage point these colonies of microorganisms can be seen as black stains on the white dolostone. The cyanobacteria and algae aren't just innocuous cliff dwellers, but instead play a role in the nutrient cycling of the cliff ecosystem, absorbing sunlight through the semi-translucent rock, and imputing nutrients into an otherwise depauperate ecosystem. The Bruce Peninsula is one of only a handful of places on Earth where cryptoendolithic organisms have been studied.
After several kilometres of fairly rugged trail I began a descent towards the coastline past thick slabs of dolostone that fell from the cliffs centuries ago, each now supporting their own garden of trees and shrubs. The Swainson's Thrushes sang all around as I dropped further and further down. Just before reaching the cobble beach, the trail passed below a massive overhanging slab. The slab protruded from the forest like a great bird's beak. Eight metres long and almost as wide, it sheltered a patch of bare soil, starved of rain water and sunshine, nothing grew there, a stark contrast to the thick forests that surrounded the outcrop. It's a fantastic natural sculpture, unexpected along this trail, while simultaneously not out of place in this land of geological wonder.
Earlier on the trail I came across several potholes, including one with the whimsical name, the Giant's Cauldron. These potholes or kettles were formed beneath glacial ice, where free flowing water formed a small whorlpool. Stones gathered up by the whirlpool were spun around and around wearing holes into the rock. The potholes stopped growing when the water flow subsided or the stones that chiselled them eroded to nothing. The Giant's Cauldron was about the size of, well, a very large cauldron, but just down the trail was an even more impressive one, the Lion's Head Pothole. This one was at least three metres deep and about a metre and half in diameter. There was a wonderful little portal in its side, that allowed one to squeeze right inside of the pothole. From within, the smooth stone wall directed your out of a sky light towards a canopy of Sugar Maple (Acer saccharum) and American Beech (Fagus grandifolia). Standing literally within the rock, an eerie silence prevailed.
The Lion's Head Potholes claims another curious naturalist.
Photo: Mark Conboy
The trail stepped over dozens of grykes, joints in the rock widened by weathering of the basic dolostone by slightly acidic rainwater. Small caves peaked out of the leaf litter; I wondered if they led to larger caves, caverns, perhaps as yet unexplored. The trail was rocky and never flat, each step either up or down over pock-marked rock. The pocks, or vugs in geological parlance, were formed as the dolostone itself was formed. Dolostone is essentially limestone that has been infused with magnesium. The original limestone, the precursor to the dolostone I navigated over all evening, was laid down in a massive coral reef sometime during the Silurian period (443 to 416 million years ago). This reef, which essentially forms the backbone of the Niagara Escarpment (of which the Bruce Peninsula is the northernmost extension), was formed by the growth and death of countless generations of corals and other sea creatures whose calcium carbonate shells became consolidated into solid limestone over eons. That limestone was eventually pushed underground where it was infused with highly saline magnesium-rich groundwater. The magnesium replaced the lime, changing the limestone to dolostone. That conversion resulted in some loss of rock volume, and that's how the vugs were formed. Had this dolomitization process not occurred we might not have the dramatic scenery of the Bruce Peninsula we see today. Dolostone, though it can be weathered, as evidenced by the potholes, grykes and caves along the trail, and large piles of talus below the cliffs, is far less resistant to erosion than limestone. Perhaps the limestone would have been eroded millennia ago, leaving a more or less flat shoreline, similar to the Peninsula's western shore. But the dolostone has persisted, giving us the dramatic views and ancient cedar forests of the Lion's Head.
The trail lead to a pleasant campsite under the shade of cedars and Red Maples (Acer rubrum). I pitched my tent near the cobble beach and settled in for a night apart from the rest of humankind.
In the morning, I found myself ascending to the cliff tops once again. Black-throated Green Warblers (Setophaga virens) were singing in profusion; it seemed that I was never out of earshot of one all morning. The woods were simply overrun with those pretty little songsters, but it wasn't long before my attention turned from the birds to the trailside plants. The Bruce Peninsula supports over forty species of orchids, most of which I didn't expect to find the Lion's Head; they are inhabitants of bogs, fens, swamps and alavars - habitats I simply didn't pass through on my hike. But these high and dry cedar woods do support a handful of species, including two biogeographical oddities: Menzies' Rattlesnake Plantain (Goodyera oblongifolia) and Alaska Orchid (Piperia unalascensis).
The tiny flowers of an Alaska Orchid (Piperia unalascensis), a western species with a disjunct Great Lake population.
Photo: Mark Conboy
Both the rattlesnake plantain and the Alaska Orchid are western disjunct species. Both are primarily distributed in western North America, but they can also be found in pockets isolated pockets elsewhere. The Alaska Orchid is the more extreme example of this pattern. Its main distribution extends from southern Alaska to Baja California. Disjunct populations occur on the Great Plains, in eastern Canada and of course, in the Great Lakes Basin. It's likely that Alaska Orchid enjoyed a much broader prehistoric distribution, that linked all of the disjunct populations to the species' main western range. For some reason, the Alaska Orchid's range contracted into the discrete populations we see today. Though less dramatically, the rattlesnake plantain also has a similar disjunct pattern and probably has a similar biogeographic history. Perhaps it was the presence of such disjunct species that caused American botanist M.L. Fernald in the 1920's, to hypothesize that the Bruce Peninsula was an unglaciated relict, harbouring species that once enjoyed a wide preglacial distribution in an ice-free refugium. We now know that unequivically, the Peninsula was completely ice-covered for several thousand years and that the disjunct distribution of orchids and other species must be explained by other means.
Another plant caught my attention on several occasions throughout the hike. The Northern Holly Fern (Polystichum lonchitis) is a relatively rare species in Ontario, but evidently there is a healthy population on the Bruce Peninsula. Beyond ancient trees, disjunct orchids, and unusual ferns, the Bruce Peninsula harbours other botanical treasures, including significant concentrations of range-restricted Dwarf Lake Iris (Iris lacustris), Lakeside Daisy (Hymenoxys herbacea), and Tuberous Indian-plantain (Arnoglossum plantagineum).
Northern Holly Fern (Polystichum lonchitis) and Maidenhair Spleenwort (Asplenium trichomanes).
Photo: Mark Conboy
But as I said, the Massasauga Rattlesnake was the main reason I visited the Bruce Peninsula. Rattlesnakes were extirpated from my home county of Norfolk and most of the rest of Southwestern Ontario long ago, although there are remnant isolated populations at either end of Lake Erie. The species' last true haven is the Bruce Peninsula and the Georgian Bay coast. In the case of Ontario's Massasauga Rattlesnakes, there is a significant amount of genetic differentiation and geographical isolation between the Bruce Peninsula and Georgian Bay populations. Even though these two rattlesnake populations exist in close proximity, they are actually rather isolated from one another, and that can have some important biological consequences.
Gene flow is important to maintaining genetic diversity, and good genetic diversity can help with disease resistance and adaptation to changing environmental conditions. Isolated populations of snakes and other organisms tend to have limited genetic diversity because of a lack of immigration from other populations (immigrants bring new genetic materials) and inbreeding.
Massasauga Rattlesnake (Sistrurus catenatus).
Photo: Mark Conboy
The snakes of the Bruce Peninsula are isolated from those of eastern Georgian Bay by water (and also intensive agriculture and road development on the southern part of the peninsula). Massasaugas, despite their fondness for wetlands, are unable or unwilling to undertake long distance swims, so the Bruce Peninsula snakes are effectively stuck on their own island, separate from their conspecifics to the east. Indeed open water is such an effective barrier to rattlesnake dispersal that Lyal Island, a mere 1.3 km off the western shore of the Bruce Peninsula, harbours its own genetically distinct population of Massasaugas. At some time in the past, Masassaugas colonized the island, but since that time, emigration from the main peninsula population has been all but nonexistent, allowing the Lyal Island snakes to develop their own genetic identities, apart from the Bruce Peninsula snakes.
Isolated populations are not necessarily a bad thing, especially if they are large, and genetic diversity can be maintained to some degree through mutations; so the Bruce Peninsula rattlesnakes are not likely to disappear because of inbreeding or something like that, at least not any time soon. What is most interesting about the isolation and genetic uniqueness of the peninsula's rattlesnakes (and it's orchids too, no doubt), is that it demonstrates a simple biological fact: not all members of one species are the same. I argue that each and every distinctive population should be conserved as though it were a distinctive species. In the case of Massasauga Rattlesnakes, we need to insure that the Bruce Peninsula population is receives proper conservation, and so too does the Lyal Island population and the many genetically discrete populations on Georgian Bay's east coast, each as though they were a different species. It would certainly be a tall order, but it would be the right conservation approach.
