The Carolinian Zone and the Deciduous Forest Region

There is some inconsistency as to the Forest Regions of Ontario. The southernmost part of Ontario has been known as the "Deciduous Forest Region" as shown in  Trees in Canada by John Laird Farrar published in 1995.

However, in the updated version of Trees in Canada from 2017, the Deciduous Forest Region is now shown as the "Carolinian Forest Region".

Going to the Natural Resources Canada website, they too have switched from Deciduous Forest Region to Carolinian Forest Region. The site was modified in 2017.

Canada Forest Classification

Now going to the Ontario Ministry of Natural Resources and Forestry, published in 2014 and updated in 2019, the Deciduous Forest Region is just that!

Ontario Forest Regions

This is an inconsistancy. Maybe the Carolinian Canada website can shed some light.

Carolinian Canada

Keeping in mind that the article is dated previous to 2004, Carolinian Canada states "we would like to see Deciduous Forest Region used instead of Carolinian Zone. We would prefer Carolinian as a label for those associations within the Deciduous Forest Region in which Sassafras and Tulip Tree are dominants".

Gerry Waldron, author of Trees of the Carolinian Forest: A Guide to Species, Their Ecology and Uses, devotes a whole chapter to "Confusion in the Carolinian Zone". The book was published in 2003 and provides an excellent description of the problems with the term "Carolinian".

Well, let's look at the forest region itself. It includes the area south of a line drawn from Grand Bend to Toronto (the southwestern part in red on the map below) plus a narrow strip along Lake Ontario (the eastern part in pink).

The southwestern part has about 24 species of trees that do not grow in the eastern part. These have traditionally been called "Carolinian" species.

On the other hand, there are  species that grow naturally in the eastern part but not the southwestern part. This includes northern species of White and Black Spruce, Paper and Gray Birch, Red Pine, Balsam Fir and Striped Maple. The eastern part is also the northern range for Pitch Pine.

There are really only two species that grow throughout the entire Deciduous Forest Region, that are unique to that region. These are Black Oak and Chinquapin Oak.

There are a dozen species of trees commonly found throughout the Deciduous Forest Region but have a range into select parts of the Great Lakes-St. Lawrence Forest Region. These are: Black Maple, White Oak, Bitternut and Shagbark Hickory, Butternut, Witch-Hazel, Blue Beech, Eastern Cottonwood, Rock and Slippery Elm, Hackberry and Eastern Red Cedar.

There are also three species almost unique to the southwestern part of the Deciduous Forest Region, but grow also in a random location (not in the eastern part). Hill's Oak also grows on the far end of Lake Superior near the U.S. border. Swamp White Oak also grows in a small pocket in Quebec, near the U.S. border. American Plum grows in Southern Manitoba near the U.S. border.

The southwestern part of the Deciduous Forest Region is unique from the eastern part, which is probably why the term "Carolinian Zone" has been used, and Carolinian species used to indicate unique species to that region (there are many!).

Why is the term Carolinian used anyway?? There are varying opinions, but it makes sense that it refers to the "Carolinian Forest" in the United States, from which certain species reach their northern limit in Southern Ontario.

But wait, there is no Carolinian Forest Region in the United States. The "Eastern Deciduous Forest" is the one that lies along the Great Lakes and does not include North or South Carolina. However, historically this forest region did include the Carolinas hence the term "Carolinian".

US Forest Service Regional Offices

Then there is the "Carolinian Zone", an unofficial term. It refers to the southwestern part of the Deciduous Forest Region.

This website uses the term "Deciduous Forest Region" and the term "Carolinian Zone" to refer to the southwestern portion of that region.