Environmentally Significant Areas

Environmentally Significant Areas (ESAs) are natural spaces within Toronto’s natural heritage system that require special protection to preserve their environmentally significant qualities. There are 86 Environmentally Significant Areas in the city.

It may come as a surprise in a city as densely populated as Toronto that many high quality natural areas still remain. Most of these natural areas are found in ravines, river valleys and along the waterfront, where they form the core of the City’s natural parklands system. They contain forests, meadows, wetlands and landforms, support an extraordinary variety of plant and animal life, and provide opportunities for people to experience wilderness in the city.

What Makes Environmentally Significant Areas Special?

Each Environmentally Significant Area has one or more of the following environmental qualities:

  • They are home to rare or endangered plants or animals.
  • They are large, diverse and relatively undisturbed which many plants and animals need to survive and reproduce.
  • They contain rare, unusual or high quality landforms that help us understand how Toronto’s landscape formed.
  • They provide important ecological functions that contribute to the health of ecosystems beyond their boundaries, such as serving as a stopover location for migratory wildlife.

Did you Know?

A total of 2, 698 ha or 4% of the city’s land area (66,750 hectares) qualify as Environmentally Significant Areas, equivalent to almost 17 High Parks or 8 Central Parks.

Environmentally Significant Areas are home to an extraordinary variety of plants and wildlife including:

  • 369 significant plant species
  • 175 species of birds
  • 16 species of reptiles and amphibians

Ravine Strategy

Most Environmentally Significant Areas (ESA) are located in ravines and along the waterfront. The city is developing a Strategy to help guide future protection, management and use of the ravine system.

Glen Stewart Ravine

Glen Stewart Ravine

The Glen Stewart Ravine was originally designated an ESA in 1982 by the Toronto and Region Conservation Authority (TRCA).  It was again designated as an ESA in 1992 by the City of Toronto and again in 2007.  Most recently, in a 2012 study, Environmentally Significant Areas (ESAs) in the City of Toronto, the Glen Stewart Ravine was included in the list of 103 City of Toronto ESAs.  It meets the following criteria:

  • Criterion A: rare species and communities
  • Criterion C: large habitats, high diversity
  • Criterion D: ecological functions.

The most important aspects of the ecology of the ravine are the diversity of native flora and of bird species.  This diversity is related to the diversity of habitat within the ravine: the well-developed structure of the canopy, sub-canopy and ground layer, the maturity of the forest canopy, and the diversity of the microclimatic conditions related to seepage slopes, dry openings and shaded, rich forest.

The 2007 study done by North-South Environmental included the following information.

Vegetation Communities:

The forest is largely dominated by red oak (Quercus rub).  The sub-canopy consists of red maple (Acer rubric) and Norway maple (Acer platanoides).  The shrub layer is dominated by witch-hazel (Hamamelis virginiana) and alternate-leaved dogwood (Cornus alternifolia) with occasional Sassafras (Sassafras album).

The ground layer is patchy and diverse, featuring native forest species such as Virginia waterleaf (Hydrophyllum virginianum), fans Solomon’s-seal (Maianthemum racemosum), starry fans Solomon’s-seal (M. stellatum) and sweet-cicely (Osmorhiza claytonii).  There is considerable diversity associated with microclimatic variations on the slopes.  Rich shaded areas support additional forest species such as rose twisted-stalk (Streptopus roseus) and white trillium (Trillium grandiflorum).  The edge of the forest along Glen Manor Drive and an open area at the north end of the ravine, are dominated by non-natives, such as Manitoba maple and Norway maple.

Norway Maple seedlings

These non-natives grow quickly, produce a dense canopy and out-compete native species. When these trees uproot, they contribute to further erosion of the steep slopes that they are growing on.  Their presence greatly reduces the likelihood of natural regeneration of native species.


Though the ravine is located in the Carolinian zone, the flora is largely typical of the Great Lakes-St. Lawrence Forest region.

One hundred and twenty-two flora species have been identified within the ravine (92 native and 30 non-native species).

Twenty-four spring ephemeral flora species were noted in the ravine.  Spring Ephemerals are adapted to flowering before the leaves in the canopy have fully expanded, taking advantage of the increased light levels to obtain energy to reproduce and grow.  Norway maple, particularly, threatens diversity of spring ephemerals, as it leafs out earlier than other tree species and its leaves are larger, reducing light available for the ground flora.

Some of the most significant species originally noted in the ravine in the 1980s were not seen in 2006 surveys, such as, trailing arbutus (Epigaea repent), poke milkweed (Asclepius exaltata) and interrupted fern (Osmunda claytonii).

Some significant flora and spring ephemeral species surveyed in the ravine include:  White Baneberry (Actaea pachypoda Elliott), Marsh Marigold (Caltha palustris L.), Two-leaf Toothwort (Cardamon diphylla), False Solomon’s Seal (Maianthemum racemosum), and Bloodroot (Sanguinary canadensis L.).



A total of twenty-two wildlife species was noted in the Glen Stewart Ravine.  Most of the diversity was in bird species.  Fauna mainly includes bird species that can nest in a variety of large and small habitats, such as American Robin, Black-capped Chickadee and Common Grackle.    However, a few forest-dependent species were noted within the ravine, including Wood Thrush, Great-crested Flycatcher and Red-eyed Vireo.  Thicket-nesting species were less common, including only Gray Catbird.  Cavity-nesting species Downy Woodpecker and Northern Flicker were abundant.  One sighting of a Canada Warbler was made in June of 2006.  This species was identified in 2008 as nationally threatened.  Two other significant species noticed in the ravine are the American Redstart and Wood Thrush.


Generally, the ravine was considered in fair to good condition.  The concerns are with the proliferation of non-native species and soils exposed in some areas by erosion and trampling.

Management of Norway maple, Manitoba maple, Japanese knotweed and tartaric honeysuckle was recommended in the report.  Managing of erosion near tree roots is a priority.  Ad hoc trails needed to be managed – by closure – and primary trails surfaced or boardwalked to reduce impacts.


Since this report in 2008, the City has been implementing the Glen Stewart Ravine Management Plan which attempts to address these concerns, and to reestablish native species and improve habitats.


These excerpts were taken from:

Appendix B – Inventory and Assessment Reports Prepared by Schollen & Company Inc., Brown Engineering Ltd. & Co. and Urban Forest Innovations Inc., in 2008

The City’s Glen Stewart Ravine Management Plan can be accessed here:

Glen Stewart Ravine Management Plan Executive Summary October 2008, prepared by Schollen & Co. Inc with North-South Environmental Inc., Lura Consulting, Urban Forest Innovations Inc, Brown & Company Engineering Ltd., and GeoTerre Ltd.









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