Friends of the Cawthra Bush
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by Paul F. Maycock, Forest Ecologist,
Erindale College, University of Toronto.
June, 17, 1998
In early summer 1959 while conducting a survey of the Deciduous Forests of extreme Southern Ontario (Maycock, 1963), I came across an extensive area of forest at the Dixie interchange on the Queen Elizabeth Highway. Much later I was to learn that this had long been known as the Cawthra Forest. Later, in 1969, I moved from McGill University to Erindale College of the University of Toronto, and came into contact with a number of biologists and naturalists who were keenly interested in this forest complex and some were involved with ecological assessment research for the Ministry of Natural Resources who was searching for candidate nature reserves. Throughout the province, Cawthra Forest was highly rated and so it should have been because of its many unusual features. At the time I thought how fortunate for the City of Mississauga that it had such an interesting large area of old growth natural forest which is so useful for education, nature conservation and for nature appreciation and the recreation of its citizens.
This stand of deciduous forest was quite extensive and variable and I selected a higher better drained mesic section and quantitatively sampled it for its composition in 1959. It contained a total of 16 different tree species, 13 in the upper canopy and 3 in the lower. Of these Sugar Maple (Acer saccharum) was the most important with an importance value of 119 of a possible 300 for the stand. The second species was White ash (Fraxinus americana) with importance of 50, followed by Black Cherry (Prunus serotina), importance 43, and Basswood (Tilia americana) importance 24 and White Elm (Ulmus americana) with importance also of 24, the latter forming about 14% of the standing trees. Other tree species with their importance included Pin Cherry (Prunus pensylvanica) (8), Paper Birch (Betula papyrifera) (8), Large toothed Aspen (Populus grandidenta) (7), Red Maple (Acer rubrum) (6), Silver Maple (Acer saccharinum) (5), Red Oak (Quercus rubra) (3), Yellow Birch (Betula lutea) (2), Serviceberry (Amelanchier arborea) (2), Beech (Fagus grandifolia) (1), Hop Hombeam (Ostrya virginiana) (1), and Chokecherry (Prunus-virginiana) (1). On the basis of these quantitative contributions to the composition of the forest we can describe it as a Sugar Maple119 - White Ash50 - Black Cherry43 forest type.
Two comments should be made about the tree composition. Although not too important, some species indicated past disturbance and successional development, including Large-tooth Aspen, Pin Cherry and Paper Birch. The complement of trees did not include any considered to be strongly Carolinian, although this cannot be considered in any way criminal or neglectful, because the site is influenced by colder than normal microclimate and it and the surroundings were seasonally quite wet. As well, many of the dominants in the Cawthra forest are also dominant or important in stands with a component of Carolinian trees. From a successional or developmental aspect, the forest is gradually trending toward a terminal or climax situation for this region. Most of the reproduction is Sugar Maple (163 of a total value of 200) and Beech is also entering the stand.
The understorey was quite striking in that it was heavily populated by a great variety of tree seedlings, shrubs and herbs, actually a total of 75 were recorded. These populations vary seasonally as in all deciduous forests but major members contributing to biomass included Allium tricoccum) (Wild Onion), Erythronium americanum (Dog-tooth Violet), Maianthemum canadense (Wild Lily-of-the-Valley), Hepatica acutiloba (Hepatica), Osmorhiza claytoni (Wild Licorice), Smilacina racemosa (False Solomon's Seal), Trillium grandiflora (White Trillium), Viola pensylvanica (Yellow Violet), and Arisaema atrorubens (Jack-in-the-pulpit). There was great variety and some groups were represented by a number of species - 5 ferns, 3 different violets, and fully 8 different species of Carex (Sedge) - C. albursina, C. gracillima, C. intumescens, C. pedunculata, C. rosea, C. plantaginea, C. communis and C. leptonervia.
Although Carolinian trees were not well represented, many understorey plants are in this group - Cryptotaenia canadensis (Honewort), Carex albursina (Wide Sedge), Dicentra canadensis (Squirrel Corn), Hamamelis virginiana (Witch Hazel), Leersia virginica (Cutgrass), Menispermum canadense (Moonseed Vine), Viburnum acerifolium (Maple-leaved Viburnium) and Viola canadensis (Canada Violet), to name a few. Interestingly, there is also a component of northern species which are uncommon southward, but which are found in the Cawthra forest. These are Prunus pensylvanica (Pin Cherry), Clintonia borealis (Blue-bead Lily), Viola pallens (White Violet) and Streptopus roseus (Rose Mandarin). It would seem that Cawthra has the best of both forest worlds in Ontario - north and south.
At a time when the scientific community is strongly involved with the phenomenon of diversity, the species richness found at Cawthra is striking, not only in terms of numbers, but also in variety.
The writer has been working in mesic old growth deciduous forests throughout the North Temperate Region and has quantitatively sampled them in Japan, China, Ukraine, Poland, Slovakia, Czech Republic, Yugoslavia, England, eastern United States, as well as Canada. He is presenting a paper on the biodiversity of these forests in Florence, Italy in July at the Seventh International Congress of Ecology. Having assembled a body of quantitative data on these forests, I was interested to see how the Cawthra Forest compared. The highest species number in any of my stands was 127 and the lowest only 17. Cawthra stood 50th in a total of 60 stands with 92 species. Thus plant diversity is quite high here and with the finds for salamanders and other organisms, it is probably true for most biological phenomena. I was quite surprised at this result because comparatively Cawthra is quite north latitudinally in comparison to many of the other stands.
The structural features, the compositional aspects, the environmental and ecological characteristics emphasize the old growth deciduous forest nature of the Cawthra Forest. It is a unique ecological entity, the like of which is rapidly disappearing in Southern Ontario. It has intrinsic value for study, for research, for a benchmark to record environmental and other ecological changes, a diverse haven for birds, animals, plants and other living organisms, and above all a place of natural wonder. Old growth systems are being set aside and protected throughout the world because of their tremendous ecological versatility. When limited public access is made available, the public is enthralled by them and more so the older they become.
If the activities of managers in the city of Mississauga within Cawthra Forest in the past 10 years are examined, it seems they are quite unappreciative of its natural values - a sewer corridor, the introduction of foreign plantings with the thought of increasing diversity, it will do the opposite - destroy natural diversity and increase that of weed species. It would seem they are attempting to create a park of it. A park can be created almost anywhere and on any site. There is just one opportunity to set up an old growth system and establish a set of regulations to perpetuate it. If the opportunity is let slip past, it is gone forever. There are parks throughout Mississauga. How many old growth forests are there?
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