Forests are almost always spoken of in terms of the trees that define their appearance. Carolinian forest in Ontario are dominated by two tree species: American Beech (Fagus grandifolia) and Sugar Maple (Acer saccharum), but they also commonly contain Basswood (Tilia americana), Red Maple (Acer rubrum), Red Oak, (Quercus rubra), White Oak (Quercus alba) and Bur Oak (Quercus macrocarpa).

Sassafras. Photo by Alan Ernst.

Tulip Tree Leaves. Photo by Alan Ernst.

Harbinger of Spring. Photo by Daniel Reed at www.2bnthewild.com.

What makes the Carolinian forest unique though is the presence of rare plants found only in this ecosystem including trees and shrubs such as the Kentucky Coffee Tree (Gymnocladus dioicus), Black Gum (Nyssa sylvatica), Black Walnut (Juglans nigra), Sassafras (Sassafras albidum), Pawpaw (Asimina triloba) and Tulip Tree (Liriodendron tulipifera), together with herbaceous plants like the Harbinger of Spring (Erigenia bulbosa). Forty percent of Ontario's rare plants can be found only in the Carolinian forest.

Trees have a way of surviving that is different from smaller plants. Trees must compete with each other for light: the more mature a forest is the taller the trees are, the fewer trees are present and the higher up the tree canopy is.

That is why cutting into a tree beyond its protective bark can be very harmful. Trees need to produce new vascular tissue every year as the old tissue dries out and becomes part of the tree's central heartwood. This is a major difference from herbaceous plants, which die to the ground every year. Herbaceous plants have vascular tissue in the centre of their stems, where it is most protected in the short term.

Because Carolinian forests are almost entirely deciduous, they look very different in winter than they do in summer. Deciduous trees shed their leaves every fall and grow new leaves in the spring.

These forests are aglow with light green in the spring when there is still a great deal of light penetrating to the forest floor and new leaves are opening from their buds. In summer, these forests become darker, as the leaves darken and grow to capture sunlight, blocking sunlight from the plants below. As a result, many herbaceous plants in these forests flower in spring to take advantage of the available sunlight and become dormant in summer, losing their leaves and disappearing from view during the time when there is less light.

Trout Lily. Photo by John MacRae.

Jewelweed. Photo by John MacRae.

White Trilliums. Photo by Alan Ernst.

Plants such as ferns that are adapted to lower light levels remain. Where taller trees are not growing as densely, there is a greater number of shrubs in the understory. These shrubs are often spindly and tall and take on horizontally branching forms as they stretch up and out to enable their leaves to reach the filtered light. Many of these shrubs have intriguing flowers, such as Witch-hazel (Hamamelis virginiana), as do many Carolinian tree species (e.g. the Tulip Tree, Liriodendron tulipifera). The presence of many flowering trees and shrubs is another unique feature of Carolinian forests.

Another group of organisms that is very important in forests is the fungi. Fungi used to be considered plants that lack chlorophyll.

Mushroom. Photo by Barry Cherriere.

They are now considered to be a distinct group, separate from plants, but are still often discussed in the same context. Fungi are composed mostly of thin, threadlike structures that live underground or inside plant tissues. We only notice fungi when they send out their fruiting bodies, some of which are commonly called mushrooms, but it is the invisible networks that do the work that fungi are famous for: decomposition.

Some fungi exist with other organisms in associations called symbiosis. In some cases structures called mycorrhizae are formed from the tissues of both fungus and plant acting in a mutualistic way so that fungus habitat is often limited to the area around or inside the actual tissue of other organisms, often trees.

The term 'symbiosis' means 'living together, and may be 'parasitism' where one organism feeds off the other in a harmful relationship or may be 'mutualism' where both organisms benefit.

Fungi on tree. Photo by Barry Cherriere.

The main location for forest fungi is on or near trees where you can easily find them on both living and dead trunks or on rotting logs.

These fungi may be living parasitically on the tree, might be behaving in a mutualistic way, or might be simply feeding of already dead tissue which is called saprophytism.

Other less conspicuous organisms in forests include the mosses...

and lichens...

Both groups rely on outside moisture because they lack vascular tissue and so are often found in moist woods. In times of drought they go dry and dormant but do not necessarily die. Lichens are very sensitive to pollution and have been greatly reduced in numbers locally over the last century.

Tree and Shrub Species of Carolinian Forests

Hepatica. Photo by Alan Ernst.

Herbaceous and Vining Carolinian Forest Plant Species