Carp Barrens Ecology

Rising above fertile farmland, the Carp Hills are formed from a 13 km long, 3 to 4 km wide band of Canadian Shield, the only substantial outlying island of Shield in southern Ontario. About 30% of this area consists of large expanses of rock with patchy vegetation called the Carp Barrens.  Outcrops of exposed bedrock are folded into glacial-scraped ridges and troughs of provincially significant wetlands and ponds.  This generally acidic and extreme environment supports plants uncommon or rare in the Ottawa area.  Scattered trees, shrubs, sedges, and grasses grow in small pockets of soil or wherever they can put down roots to extract limited nutrients and moisture.  Rocks are covered with mosses and lichens that, if undisturbed, can survive complete dehydration.  Several species at risk breed in the special habitat:  Blanding’s turtle, Eastern Whip-Poor-Will, Common Nighthawk, and Snapping turtle.

Because of it unique character, the Carp Barrens are a candidate for the designation as a Provincially Significant Area of Natural and Scientific Interest (Life Science).


The Carp Barrens (like Gatineau Park) are composed of the oldest rocks in the Ottawa area, which were formed in the Precambrian Era over 1 billion years ago and known as the Canadian Shield.  The Barrens are underlain by gneiss, schist, marble and granitoid rocks, capped in a few places by Lower Paleozoic strata.  This geology creates an acidic environment, which may be moderated by the more alkaline substrate.

Shard of Mica.

Gneiss contains mica.  There are at least two, small shallow mica mines found on the Barrens.  More than a century ago, Eastern Ontario was one of the mica mining capitals of the world.  The mica was fashioned into sheets of glass-like, thermal windows for lanterns and wood stoves.  Mica is stable when exposed to electricity, light, moisture, and extreme temperatures.


A Land of Extremes

Rock barrens have a wide variation in soil depth and in water-holding capacity over a short distance. These variations are responsible for the mosaic patterns of vegetation. The rock is acidic and generally contributes to the formation of acidic soils. 


Spring in the Carp Barrens is a special time of year.  What moisture remains from the melted snow and the early rains causes an explosion of flowers and greenery in the spring as plants reproduce while conditions are favorable. The mosses and lichens rehydrate and extend fruiting bodies, shown in rusty orange in the photo.  Blueberries bloom in the background.

Because of the extreme conditions and poor nutrients, plants grow slowly on the Barrens.  The Red Oak and the Large Tooth Aspen near the road are probably well over 100 years old and have undoubtedly survived some brush fires.

Common trees on the southeastern side of the Barrens are:  White Pine, Paper Birch, Red Oak, Trembling Aspen, White Spruce, and Red Maple.  Four young Tamaracks are growing in water with the Leatherleaf shrubs.  Many few trees and shrubs were victims of the summer 2012 drought. Bur oak (which is normally drought tolerant), white spruce, and juniper were particularly hard hit.

Pink Lady’s-slipper orchids.

Common shrubs are: Speckled Alder, Winterberry, Leatherleaf, Blueberries, Common Juniper, Choke Cherry, and Wild Raisin Viburnum, some of which prefer acid soil.

Spring flowers are:  Pale Corydalis, Wild Columbine, Bicknell’s Geranium, and Pink Lady’s Slipper.  Common Polypody fern perches in shallow crevices. The uncommon Fernald’s Sedge and Spikemoss are highlighted in the 1992 ANSI report.



Poor fen. Photo by Holly Bickerton.

During the Carp Barrens Trail Study in 2019, a total of twenty regionally rare plant species were found (Brunton, 2005 – see More Information).  Some of these were growing on floating mats of sphagnum moss in a poor fen.  Poor fens form on relatively acidic substrates where there are few plant nutrients.  They are peat-based systems that are relatively rare in the limestone-rich Ottawa area. The poor fen mat contained two regionally rare (less than five known locations) species :  Filiform Cotton-grass (Eriophorum tenellum) and Bog Buckbean (Menyanthes trifoliata).

The Carp Barrens are characterized by a tapestry of mosses and lichens that form a thin layer over the nutrient poor, acidic rock.  Crustose lichens, common on the Barrens, grow less than a millimeter per year (Easton, 1994).  Human traffic can quickly erase decades, if not more than a century, of growth in a short period of use.

This is a fragile and special area. It can take years for plants to regenerate.

Species at Risk

Five Species at Risk (SAR) are known to call the Carp Barrens home:  Eastern Whip-poor-will (THR), Common Nighthawk (SC), Blanding’s Turtle (THR), Snapping Turtle (SC), and Eastern Wood Pewee (SC).  The Eastern Whip-poor-will and Common Nighthawk are ground nesting birds easily disturbed by human activity. 

Turtle nests, SAR bird breeding activity (night calling), and a Common Nighthawk nest have been documented in the Carp Barrens, making it Category 1 Critical Habitat.

Common Nighthawk on the Carp Barrens. (Photo by Chris Busby.)