The Bruce Peninsula Part VI: An Alvar Wonderland

 *Part I* *Part II* *Part III* *Part IV* *Part V* *Part VI* *Part VII*

One of the Bruce peninsula's most remarkable and noteworthy of natural treasures is its abundance of a unique habitat known as an alvar. I've mentioned the term and habitat type a number of times during this series but now it's time to dive head first into this globally rare occurrence and dedicate some much deserved attention to its botanical wonders.

Alvar pavement complex on the northern Bruce peninsula

As mentioned, alvars are a globally rare habitat and only occur in the Great Lakes of North America, and the Scandinavian/Baltic region of northwest Europe. It's a habitat characterized by flat, exposed limestone/dolostone bedrock with very little soil accumulation. Really, it looks like an immense parking lot with patches of accumulated soil, plants, mosses and lichens. The previous glacial epoch scoured this landscape clean of organic material and often left signs of its presence as long gashes, grooves, scrapes etc. in the bedrock. Ohio's Kelley's Island in Lake Erie is well known for this stunning geological feature. 

Ontario is the official alvar headquarters of North America with 85% of the continent's remaining habitat. The Great Lakes region's alvar can be organized into five general categories: pavement, grassland, savanna, shrubland, and shoreline. We've seen shoreline alvar previously at both Singing Sands and Halfway Log Dump; most of this post will deal with the pavement sub-type. It's taken nature literally thousands of years to reclaim the landscape and soil to accumulate enough to support plant life again.

And plant life has definitely returned! Alvars naturally result in a grassland-type ecosystem, and a unique one at that. The landscape is punished nearly year round by the elements and makes for a harsh place to live. The winters are bitterly cold and snow-filled; the summers bake the landscape to a dry crisp. This, along with the very shallow, if any soil accumulation does a great job of keeping trees at bay and the alvars open. Spring, however is the alvar's time to shine, at least botanically. The melted snows and seasonal rains fill the alvar's shallow depressions and fissures with water and creates a stunning rock garden of epic proportions. The botanical diversity is surprisingly impressive and even offers some evolved specialists that only call this limestone parking lot home as you'll come to see.

Large Yellow Lady's Slippers (Cypripedium pubescens)

One of the most obvious and conspicuous of wildflowers to colonize the alvars in the Bruce region is the large yellow lady's slipper (Cypripedium pubescens). Back in Ohio this species is largely restricted to high-quality woodlands with rich, fertile soil but up here they are much more of a generalist and grow just about anywhere. The dry, shallow, gravelly soils of the roadsides and alvars seem to be their favorite haunts, though.

Rob inspecting an alvar fissure for the rare fern we were after

Walking out onto the Bruce's alvar pavement is like stepping onto another world. Some places are literally nothing more than pure limestone bedrock with the only life being tiny pockets of moss and lichen that can eek out a precarious existence. Large cracks and fissures aren't an uncommon sight and provide a small habitat niche for many plants, especially some of the area's rare ferns we were after.

Green spleenwort (Asplenium trichomanes-ramosum)

Green spleenwort (Asplenium trichomanes-ramosum)

If any theme keeps resurfacing during this series, it's the fact that the Bruce and adjacent areas seem to be a nexus for western disjunct species to thrive. Yet another example of this is the green spleenwort (Asplenium trichomanes-ramosum) (also see: A. viride). Green spleenwort is an uncommon species in North America but mostly found in the Mountain West and scattered locations in the Great Lakes and Northeast. Our group managed to come across a handful of sites for it, with my favorite being this clump growing literally out of the rock within a crack in the alvar pavement.

Maidenhair Spleenwort (Asplenium trichomanes)

For the few times we found the green spleenwort, we were tricked a dozen more by the common look-a-like maidenhair spleenwort (A. trichomanes). It would often grow right alongside its rarer kin and offered a great chance to see the distinguishing features: the best of which being green spleenwort's distinctly green rachis versus the maidenhair's black rachis.

Scarlet paintbrush out on the open alvar pavement

One of the alvar pavement's most distinguished of wildflower denizens is the unmistakable scarlet paintbrush (Castilleja coccinea). It occurs just about everywhere there's enough moisture and light on the Bruce and in the most pristine of areas can carpet the landscape with its brilliant color. 

Limestone Oak Fern (Gymnocarpium robertianum)

Another of the Bruce's more rare pteridophytes on my radar during our botanical foray was a big life species for me and with the help of Bob Curry, you'll remember him from my previous post on Inglis Falls and the Hooker's orchid, it quickly had a check next to its name on my list. In an isolated complex of alvar pavement was a small fissure that has housed a colony of the limestone oak fern (Gymnocarpium robertianum) for decades. If you come to the Bruce for the orchids, you should stay for the ferns! Both are in great supply on this tiny spit of the Niagara Escarpment.

Limestone Oak Fern (Gymnocarpium robertianum)

Limestone Oak Fern (Gymnocarpium robertianum)

It's never a bad thing to have such a trustworthy and consistent spot for such a rare plant, and I, for one was very thankful Bob was willing to share it. Limestone oak fern is a rarity throughout its limited range in the northern Midwest and western Great Lakes, and is at about its easternmost known locality on the northern tip of the Bruce peninsula. Its appearance is very similar to the rest of its oak fern ilk but for the glandular nature of its rachis and stipe. This gives the plant a silvery sheen at close inspection and is a bit sticky to the touch, too.

Spring makes the alvars come alive with wildflowers!

The alvars are snow and ice-covered all winter and dried to a crisp of little else but drought-tolerant grasses, sedges, mosses and lichens come summer. But that small window of opportunity in the spring makes them truly come alive! Late May into mid June allows for an explosion of wildflowers unlike little else I've seen. Our arrival was just a bit too late for the peak bloom of thousands upon thousands of the globally rare lakeside daisy (Tetraneuris herbacea) but the scenery was still spectacular.

Lakeside Daisy (Tetraneuris herbacea)

Lakeside Daisy (Tetraneuris herbacea)

Earlier on in this series I gave a brief preview of this remarkable wildflower on the alvar shorelines of Halfway Log Dump and mentioned it was hardly the best place to see them. Hopefully the photos in this post prove I was right! You'd never know the yellow blossoms of this daisy was so rare or special if all you knew was its presence on the Bruce. Lakeside daisy is an alvar specialist and is only known to occur on alvar in select areas of the Great Lakes. It was isolated long ago during the series of glacial events and evolved into its own unique being to color the limestone pavement come late May.

Blue Flag Iris (Iris brevicaulis)

It's an interesting contrast to see pure bedrock covered in millennia of accumulated moss and lichen crust and then literally right next to it see a fissure full of a wetland species like blue flag iris (Iris brevicaulis). The Bruce's alvars go a long ways in showing that no one and nothing is a finer gardener or landscape artist than Mother Nature herself.

Nodding Trillium (Trillium cernuum)

Nodding Trillium (Trillium cernuum)

I couldn't help but share one of my absolute favorite of wildflower finds during my time up north, even if its not an alvar species. After exploring a particularly awesome complex of alvar remnants, we came to a woodland stream that was flush with vegetation. All along its banks was a trillium I'd only had the pleasure of seeing once before in the nodding trillium (Trillium cernuum). It's a genuine species of the northern woods and is quickly disappearing from its southern range for reasons not fully known. It looks nearly identical to the more southern drooping trillium (T. flexipes) but for its anther's filament length. Nodding trillium's anthers hang well outside the whorl of petals on long filaments; drooping trillium's anthers are tucked back against the base of the ovary on very short, often unseen filaments.

Purple Cliffbrake (Pellaea atropurpurea)

A surprise fern find while out on the alvars was a familiar face to this Ohio botanist but yet another great rarity for the Bruce. The purple cliffbrake (Pellaea atropurpurea) isn't all that uncommon in Ohio, where it's restricted to vertical limestone cliff faces, but to occur so far north is another testament to the Bruce's affinity for fern diversity. As mentioned, I've only ever seen this species growing in a vertical fashion so it was quite the shock to see it happy as could be in the full sun on the horizontal alvar pavement.

Alvar pavement landscape

Lakeside Daisy (Tetraneuris herbacea)

Yellow and red never looked so swell together

A few more scenes of the Bruce's springtime wildflower wonder on the alvars never hurt anyone! I could spend a lot more time delving deeper into the alvar's flora. Hell, I could do an entire post on the dozens of exciting sedges that call it home, but I'll end things here and hope it's inspired you to experience this globally rare and exciting habitat for yourselves one day. I'd love to get back up there during the early summer months to experience the Bruce in a whole new way. I have one last post to share before I call this series done and I think I've saved the best for last! So check back soon and leave your thoughts and comments below. Thanks again for taking the time read and hopefully enjoy this incredible world!

- ALG -