Friends  of  the  Cawthra  Bush


Greater  Mississauga  Area

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Scanned copy, if there are errors, please e-mail me with corrections :

The Wetland Specialists
Inventories - assessments - restoration.

Friends of Cawthra Bush - C/O Donald Barber

Dear Mr. Barber:

July 6, 1998

This letter is being sent in response to the May 23, 1998 Cawthra Bush site visit. This was our first visit to Cawthra, and needless to say it greatly exceeded our expectations. We frequently visit urban woodlots for various reasons, and were surprised to note that this Mississauga forest fragment is anything but typical.

There are not many urban woodlots that can boast of a biodiversity even remotely comparable to that of the Cawthra Bush. With nearly 300 species of plants, Cawthra contains several interesting and threatened vegetative communities linked together within a small (approx. 55 acres), parcel of land.

Like all diverse, wet forest ecosystems, Cawthra also contains a myriad of faunal organisms. Some creatures are attracted to this area because it offers food, drink, or shelter, in an overly urbanized city. Others are rare, and remnant populations, using Cawthra as a last strong-hold.


It is extremely important to note, that the true significance of the Cawthra Bush can not be ascertained by a single site visit. To be accurate in estimating the value of Cawthra to wildlife and wildlife populations, a full year of observations is required.

As you know, different species use different habitats, at different times of year. This is most noticeable when it comes to birds. Due to the migratory nature of most species of birds, and their highly variable feeding behaviours, different species will use the Cawthra Bush in different seasons. Similarly, different plant species will flower in spring, than in summer or fall.

Due to the fact that the Cawthra bush is so unique within the landscape, an opportunity is offered to locate rare or threatened species. The discovery of Ambystoma jeffersonianum and Fallicambarus fodiens is testimony to this. A more thorough, season by season survey may reveal others.

Aside from the age of this forest, the simple fact that it is "wet", makes it significant. The majority of woodlots in the Golden Horseshoe are typical beech/maple forest fragments surrounded by agricultural lands. Traditionally, these "islands" of habitat have been drained to facilitate crop production. Soon after, there is a marked reduction in function and ecological productivity. By adding water back to a system, diversity can quickly be restored.

 Page 2

Cawthra is unique in the fact that it has retained some of its hydrologic function. Changes made recently to the local drainage patterns have undoubtedly had a negative effect. This misguided attempt to "improve" the health of the Cawthra Bush will most certainly diminish it's integrity.

At this point in time, the details of Cawthra's hydrology are not completely known. More study is recommended of the function of ground water in this forest, as well as the surface ponding that has thus far maintained the amphibian populations. This work should be conducted in conjunction with a Southern Ontario Wetland Evaluation.

Cawthra's uniqueness within the landscape has made it a focus of public interest. This is not surprising as more and more people become aware of the values of greenspace, and greenspace variety within our city limits. One of the reasons people are drawn to urban woodlots is because they provide the feeling of being "up-north", without the hassles of leaving city limits. This experience is significantly diminished when the woodlots themselves are urbanized. Draining forests for the purpose of bug removal deters more people from using the bush than it will attract. A forest in southern Ontario drained of its water, and thinned of dead or dying trees, is little more than a tree plantation. It's no longer a forest. It's no longer an enjoyable place to be.

Bugs, more properly known as insects, can be easily controlled through less destructive, less expensive, less controversial, and more community based means. For instance, installing nesting structures for insect eating birds is an easy way to get schools and neighborhoods involved with greenspace stewardship. It provides good public relations for local governments and generates positive public interest.

Cawthra also offers a wonderful opportunity for educational study. The value of the Cawthra Bush as an educational tool is immeasurable. Where else can someone find such an atypical woodlot for studying suburban ecology.


Too many walking trails in a forest such as the Cawthra bush may also have a negative effect on it's forest ecology. For instance, abundant trails, and overly wide trails, provide access points for Brown-headed Cowbirds. There have been several studies conducted on the importance of un-fragmented forests for breeding birds of many species. Many of which are highly susceptible to Brown-headed Cowbird parasitism. Cowbirds are not an interior forest bird, and those that are, do not have the adaptations necessary to combat this brood parasite. The Cowbird is an edge species, and the more the forest is opened up, the more the cowbird can penetrate.

Another negative impact of excessive forest thinning is increased invasive plant colonization. The most noticeable introductions will likely be garlic mustard and purple loosestrife. These two species rapidly displace indigenous species, and soon after establishment dominate the landscape. They in turn provide minimal value to the forest community, and limit more desirable species.

Opening forest canopies and thinning edges, drastically, and quite noticeably, reduces forest humidity. Many species of desirable forest insects such as beetles, and moths require precise humidities to complete their life cycles. These are the same species that are responsible for pollinating the many plants people enjoy seeing such as trilliums, trout lilies and hepaticas.

Page 3

Opening up areas allows the sun to penetrate to the forest floor, which in turn increases competition for these desirable plants by encouraging grasses, dandelions, and other typical field species to establish.


The amount of suitable habitat for F. fodiens is decreasing (Hamr, 1998). The destruction of wetlands, which has unrelentlessly occurred for generations, has caused the decline of this semi-terrestrial crayfish. Currently it is at risk of extirpation due to the lack of wetlands (Hamr, 1998). With the Cawthra Bush having a relatively good sized population, it is strenuously recommended that the de-watering of it's habitat be halted.

The A. jeffersonianum that are present are indicators of a healthy old growth forest. The Plethodon cinereus is also indicative of this due to its need for a deep layer of leaf litter (Seburn, 1997). Retention of high moisture levels on the forest floor is the only way to protect the only two identified salamander species within the Cawthra bush.

The diversity of plant species will change dramatically with the drainage of this wetland. It's rarity as a unique habitat type balances on it's hydrology. Every living creature requires water to survive, to deny an entire wildlife community of that basic right to survive is, ironically, inhuman.

Thank-you for the opportunity to respond - Sheri Ross Fish and Wildlife Technologist & Corey Lewis, Fish and Wildlife Technologist

 The Wetland Specialists
Phone (905) 643-3335 - Fax (905) 643-6641Post Script: For the purpose of conserving the Cawthra Bush, this letter may be distributed at the discretion of Donald Barber to any concerned parties.

It will make a difference!
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