EEB 337H - Families of Vascular Plants 

The deciduous forest; Ontario's "Carolinian" region

This forest region provides Ontario with its greatest diversity of plant species. This is illustrated by tabular comparison of tree species in the deciduous and mixed forests. It is worth noting that although it is described as a forest region, in fact where local conditions (e.g. vernal flooding, summer drought) are unfavorable for the growth of trees there are scattered pockets of grassland, tallgrass prairie.

The way in which this region of Ontario is recognized botanically provides a useful illustration of the importance having a comprehensive, scientific system for naming plants:

Early French explorers in what is now southern Ontario..., especially the region between the Niagara and Detroit rivers, noted with amazement the character and of the flora. In variety and lushness it seemed to belong to a much warmer climate. ...European botanists, such as Kalm and Rafinesque, who came to North America in the middle decades of the eighteenth century, noted the phenomenon, but since the continent was still under a single sovereignty had no occasion to relate their observations to a political boundary. The creation of the United States offered a new point of view: when, in the last years before 1800 and the first decades immediately following, travellers from that country passed through the southern part of Upper Canada, they were very conscious of having crossed a frontier.

Little by little it dawned upon studious observers that ...despite the interposition of a formal frontier and the broad span of inland seas, the territory under observation was a unit. From its northern limit, somewhere in canada, it stretched into the southland as far as Tennessee and the Carolinas, and even beyond. It even reached out westward and southwestward across the Mississippi. Captivated by a name redolent of the south, one investigator called, quite appropriately, the vast roughly-defined expanse, the Carolinian zone.

(Fox & Soper 1952)

Fox and Soper mapped the distributions of trees and shrubs in southern Ontario in a series of papers published by the Royal Canadian Institute (Fox & Soper 1952, 1953, 1954; Soper1956, 1962). In this way they produced an empirical description of the way in which the species diversity of vascular plants increases dramatically as one passes southwest from Toronto into the Niagara peninsula and then west beyond London toward Windsor.

However, the recent history of the deciduous forest region in Ontario has been one of

As a consequence almost all of the original forest cover in this part of Ontario has been destroyed, and only a small proportion of the total area has been allowed to regrow as forest. As a result 65 species are considered to be at risk in this region.

The map below shows how little forest cover (black) remains in Kent and Elgin counties (map courtesy Dr J. M. Bowles, University of Western Ontario).
Janemap2.gif - 11243 Bytes

Liriodendron tulipifera L. (Magnoliaceae) is one of the best known "Carolinian" trees, and is considered rare (Argus et al. 1982-1987) but not at risk.
Liriodendron tulipifera (M. Ferguson) - 22769 Bytes

Photo M. Ferguson - Royal Ontario Museum 1998.
Liriodendron tulipifera (R. Joos) - 50035 Bytes

Drawing R. Joos R. Joos 1997.


Sources:

Argus, G. W. et al. (1982-1987). Atlas of the rare vascular plants of Ontario. Four Parts. National Museum of Natural Sciences, Ottawa (looseleaf).

Fox, W. S. & J. H. Soper (1952). The distribution of some trees and shrubs of the Carolinian zone of southern Ontario. Trans. Royal Canadian Inst. 29 (II): 65-84.

Fox, W. S. & J. H. Soper (1953). The distribution of some trees and shrubs of the Carolinian zone of southern Ontario. Part II. Trans. Royal Canadian Inst. 30 (I): 3-32.

Fox, W. S. & J. H. Soper (1952). The distribution of some trees and shrubs of the Carolinian zone of southern Ontario. Part III. Trans. Royal Canadian Inst.30 (II): 99-130.

Soper, J. H. (1956). Some families of restricted range in the Carolinian flora of Canada. Trans. Royal Canadian Inst.31 (II): 69-90.

Soper, J. H. (1962). Some genera of restricted range in the Carolinian flora of Canada. Trans. Royal Canadian Inst.34 (I): 3-56.


Although this course does not deal with forest dynamics, you may want to learn more about some of the important tree species in southern Ontario by visiting the Science magazine feature, "Scaling from trees to forests." Science logo


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Please send your comments to tim.dickinson@utoronto.ca; last updated 01-Oct-2008