Rock Barrens – Geomorphology, Fire, & Prairie Warblers

Frontenac Provincial Park lies within the Grenville Province of the Canadian Shield. About 800 million years ago, the Grenville Province was a towering mountain range with peaks as high as the modern day Himalayas. Subsequent periods of erosion, sedimentation, glaciation and more erosion has created the current landscape as we see it today. The rock barrens, in their present myriad of forms and age, cover a significant portion of Frontenac Provincial Park. Geologically, the barrens are described by Christian Barber as a:

“football-shaped body of Diorite that rose up from great depths as a very hot, semifluid pluton.” (Barber 2005)

Three significant forest fires have occurred in the barrens since the mid-19th century. These fires and also the hard bedrock has limited soil generation and plant growth. Both geological and cultural histories have played a role in the creation and maintenance of these open rock barren habitats. The above picture is from the top of a ridge overlooking Slide and Buck Lakes, the most rugged area of the park that stretches from here in the south to our Rock Ridge MAPS site about 6km to the north.

This excursion involved a lot of exercise – over 10km of paddling and about 6km walking. Several pairs of loons would come over quite close to the boat and check me out. Not sure why they do this, maybe the paddling and noise stirs up prey under the surface? I’ll never get tired of seeing Loons.

These are the aforementioned rock barrens. The last fire burned this area over around 1930, which demonstrates the remarkably slow rate of succession in the barrens. The few scattered trees are no more than 5 or 6 metres tall. Eastern Towhee, Field Sparrow, Common Nighthawk and Prairie Warbler are attracted to these habitats for its absence of tree/canopy cover, presence of low shrubby growth and/or sparse ground cover.

During the morning I completed a brand new point count route through this area to boost our monitoring coverage of this unique habitat. I was also hoping to find and georeference Prairie Warblers, a recently de-listed Species at Risk that is still quite rare and isolated in Ontario. They occur along a narrow band at the southern edge of the shield – from the Frontenac Arch Biosphere Reserve in the east to the Georgian Bay Biosphere Reserve in the west. Rock barrens can be found throughout the shield but they are most widely distributed and heavily concentrated along this ecotone in central Ontario. This photo shows a small stretch of habitat incised by a wetland that held five Prairie Warblers. The deciduous tree on the right seemed to be a prominent song perch, which three gorgeous males aggressively fought over.

By the end of the day, over a dozen Prairies were located and mapped, which was a terrific reward for such a long day. I have two more “inventory” sessions for Prairies in the area still to come so there should be more of these bright yellow “buzzers” out there. This inventory will set the basic population parameters for potential future research, which would involve a more in-depth look at demographics and habitat preferences. The Prairie is one of a host of species that depends on cyclic disturbance, natural or anthropogenic, to maintain stable and viable populations. It is likely that, without another significant fire, the Prairie Warblers in Frontenac Park will be extirpated as these rock barrens mature. This is definitely a fascinating context for a detailed study…

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4 thoughts on “Rock Barrens – Geomorphology, Fire, & Prairie Warblers

  1. What a wild, interesting place. Sometimes I think there are places where you could set up a lawn chair and watch the scenery for the rest of your life and die feeling you had spent your time wisely.

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