Oak Savanna
A transitional ecosystem between open prairie and closed forest, characterized by scattered mature oak trees (10-35% canopy cover) over a prairie-like ground layer of grasses and forbs. One of Ontario's most endangered ecosystems.
Physical Characteristics
Soils: Well-drained sandy or sandy-loam soils. Often over calcareous till or sand plains. Low to moderate fertility. Rapidly draining.
Characteristic Vegetation
- Quercus velutina
- Quercus alba
- Quercus prinoidesspecies
- Asclepias tuberosaspecies
- Andropogon gerardiispecies
- Lupinus perennisspecies
- Schizachyrium scopariumspecies
- Sporobolus heterolepisspecies
- Ceanothus americanusspecies
- Sisyrinchium montanumspecies
- Asclepias purpurascensspecies
- Comptonia peregrinaspecies
- Pycnanthemum incanumspecies
- Carex pensylvanicaspecies
- Senna hebecarpaspecies
- Solidago nemoralisspecies
- Geum triflorumspecies
- Antennaria neglectaspecies
- Celtis tenuifoliaspecies
Characteristic Fauna
- Danaus plexippusfauna
- Bombus impatiensfauna
- Satyrium favoniusfauna
- Anisota finlaysonifauna
- Plebejus samuelisfauna
- Callophrys irusfauna
- Erynnis persiusfauna
- Hesperia leonardusfauna
- Anatrytone loganfauna
- Atrytonopsis hiannafauna
- Halictus ligatusfauna
- Vanessa virginiensisfauna
- Asterocampa celtisfauna
- Asterocampa clytonfauna
- Phoebis sennaefauna
Details
Description
Oak Savanna (also known as Black Oak Savanna) is a critically imperiled ecosystem in Ontario. It occupies the transitional zone between tallgrass prairie and oak woodland, with 10-35% tree canopy cover dominated by oaks, particularly Black Oak (Quercus velutina) and White Oak (Quercus alba). The open canopy allows sufficient light for a species-rich ground layer of prairie grasses and forbs.
This ecosystem was historically maintained by regular, low-intensity fire (return interval of 1-10 years). Fire suppression, agricultural conversion, and urban development have reduced Ontario's oak savanna to less than 1% of its pre-settlement extent.
Physical Characteristics
- Soils: Well-drained, rapidly draining sandy or sandy-loam soils. Often over sand plains or glacial outwash deposits. Low to moderate fertility.
- Moisture: Dry to dry-mesic. The sandy substrate and open canopy create warm, drought-prone conditions.
- Microclimate: The scattered tree canopy creates a mosaic of sun and shade patches, with soil temperatures varying widely across small distances.
Characteristic Vegetation
- Canopy: Black Oak (Quercus velutina), White Oak (Quercus alba), with occasional Bur Oak and Shagbark Hickory
- Shrub layer: New Jersey Tea (Ceanothus americanus), Lowbush Blueberry (Vaccinium angustifolium), Sweetfern (Comptonia peregrina)
- Ground layer: Little Bluestem (Schizachyrium scoparium), Big Bluestem (Andropogon gerardii), Wild Lupine (Lupinus perennis), Butterfly Weed (Asclepias tuberosa), Hoary Mountain-mint (Pycnanthemum incanum), Wood Lily (Lilium philadelphicum)
Characteristic Fauna
Oak Savanna supports a disproportionately large number of rare and at-risk species for its extent:
- Birds: Red-headed Woodpecker (Endangered), Eastern Bluebird, Brown Thrasher
- Insects: Frosted Elfin (extirpated), Karner Blue butterfly (extirpated from Ontario, host plant Wild Lupine), Eastern Persius Duskywing (extirpated, SARA Endangered), Mottled Duskywing (Endangered), numerous oak-dependent Lepidoptera
- Reptiles: Eastern Hognose Snake (Threatened)
Ontario Distribution
Rare remnants found in:
- Alderville Black Oak Savanna (Northumberland County) - one of the best remaining examples
- High Park (Toronto) - actively managed with prescribed burns
- Pinery Provincial Park (Lambton County)
- Sandbanks Provincial Park (Prince Edward County)
- Tiny fragments in Norfolk, Brant, and Waterloo counties