Oak Savanna – Friends of Old Ausable Channel

The Old Ausable Channel is adjacent to one of the most vulnerable ecosystems on the planet. Oak savanna is a globally rare ecosystem that is a transition between prairie grasslands and oak forests. More than 99% of the oak savanna in the world has been altered or destroyed. Through careful management, Pinery Provincial Park has restored its oak savanna and protects nearly 50% of the remaining oak savanna in the world.

What is an oak savanna?

An oak savanna is an ecosystem with 25-35% canopy cover – meaning 25-35% of the ground will be shaded at solar noon. This is compared to a true forest, where cover is greater than 50%. This extra light within an oak savanna allows for understory plants to grow that would otherwise be unable to survive in the thick cover of a dense forest. Some of these unique plants include:

NEW JERSEY TEA
Ceanothus americanus

WOODLAND SUNFLOWER
Helianthus divaricatus

ROUGH BLAZING STAR
Liatris aspera

oak savanna sunset — © Justin Meissen, some rights reserved (CC BY-SA 2.0) - https://flickr.com/photos/40855483@N00/15396252166

As the name might suggest, dominant trees in oak savanna include oaks, with 7 oak species common in the OAC area:

Northern Red Oak

White Oak

Black Oak

Chinquapin Oak

Dwarf Chinquapin Oak

Bur Oak

Swamp White Oak

Species at risk in oak savannas

Due to declining habitat, many oak savanna species are species at risk. Some of these species have evolved to have very specific requirements to survive, placing them at higher risk. This includes the Fern-leaved Yellow False Foxglove and the False-foxglove Sun Moth.

false foxglove — © Jeff Goddard, some rights reserved (CC BY-NC) - https://www.inaturalist.org/photos/149536808

false foxglove larger plant — © Jeff Goddard, some rights reserved (CC BY-NC) - https://www.inaturalist.org/photos/149536816

THREATS

Declines in oak savanna habitat

Declines in oak savanna habitat

– Fire suppression
– Residential development

Oak wilt disease in host oak trees

Deer browsing

The Fern-leaved Yellow False Foxglove (Aureolaria pedicularia) is a threatened plant found in the OAC. It lives in open savanna and woodland habitats with Black Oak (Quercus velutina), its preferred host tree. This plant is unique because it taps into the roots of oak trees to help supply itself with water and additional nutrients.

An emerging threat is a fungal infection called oak wilt, caused by Bretziella fagacearum. While it has not yet been detected in Canada as of 2023, it has been found very close to our Ontario border. This pathogen poses a significant risk to all oak species in Canada, as it is capable of killing trees within a single season. Since Fern-leaved Yellow False Foxglove relies on oak species to supplement their nutrition and water intake, this would have further negative consequences on their populations.

False-foxglove Sun Moth in the adult stage.

false foxglove moth — © Sarah Shearer, some rights reserved (CC BY-NC) - https://www.inaturalist.org/photos/91290825

False-foxglove Sun Moth in the larval stage.

false foxglove caterpillar — © Chris Buelow, some rights reserved (CC BY-NC) - https://www.inaturalist.org/photos/72682114

THREATS

Declines in oak savanna habitat

Decline of required host plants

– Fern-leaved Yellow False Foxglove
– Smooth Yellow False Foxglove

Declines in oak savanna habitat

– Fire suppression
– Residential development

Deer browsing

Oak savanna management

In the past, forest fires were commonly seen as only destructive in nature. We have learned in recent years that by suppressing nature’s fires, we have actually harmed nature more. Critical oak savanna habitat can be lost if fires are suppressed too heavily. Without fire disturbances, the understory of the savanna becomes thicker and denser, and the rare ecosystem beings to disappear into a thick forest. Oak savanna habitat by definition should only have about 25-30% forest cover.

A multitude of oak savanna species actually rely on fire in order to reproduce. Some species require the actual heat and flames for their seeds to be released and germinate. Other species rely on fire to burn off the leaf litter on the ground, along with any competing small shrubs and trees. An added benefit of fire is that it may reduce the impact of understory invasive species such as Garlic Mustard (Alliaria petiolata). Through careful management and prescribed burns, oak savanna habitat is further protected.

This is not a new concept to First Nations and Indigenous Peoples who have been utilizing fire to manage their lands for thousands of years. Fire was used to clear land for agriculture, to rejuvenate areas with important forage and medicinal plants, and to maintain wildlife habitat. Through this use of fire, oak savanna habitats were also rejuvenated and maintained.

Oak savanna with an open canopy due to proper management tools such as prescribed burns.

Prescribed burns can help rejuvenate oak savanna habitat by reducing plant competition.