The sugar maple-American beech forest occurs adjacent to the Collegeway.  Mature sugar maple and American beech dominate this closed canopy with red oak (Quercus rubra) as the associate.  The shrub layer is dense with choke cherry (P. pensylvanica).  The understory is depauperate but includes wild leek, Jack-in-the-pulpit (Arisaema triphyllum) and false Solomon’s-seal (Maianthemum racemosum).  The trees in this forest community are 80 to 120 years old thus contain old growth elements, and are typically 48 cm
in diameter.

The sugar maple-eastern hemlock forest occurs on the rolling floodplain of Sawmill Creek.  Mature sugar maple and eastern hemlock form a closed canopy with red oak and American beech as the associates.  The understory here is composed of meadow rue (Thalictrum spp.), blue cohosh (Caulophyllum thalictroides), tall buttercup (Ranunculus acris), large-leaved aster (Aster macrophyllus), and false Solomon’s-seal.  The canopy is 40 m in height and the trees are typically 36 cm in diameter.  Red oaks reaching 112 cm in diameter and eastern hemlock reaching 79 cm in diameter are not uncommon.

The wooded non-native valley land community also occurs along the floodplain of Sawmill Creek.   Scattered mature willow (Salix alba) and red ash form an open canopy above a subcanopy of Manitoba maple (A. negundo).  Riverbank grape and the invasive species garlic mustard, multiflora rose (Rosa multiflora), and Tartarian honeysuckle (Lonicera tatarica) are prevalent in the dense understory.  The old field community occurs in scattered locations along the edge of the site.  Common species include tall goldenrod (Solidago altissima), bird vetch (Vicia cracca), wild carrot (Daucus carota), smooth brome (Bromus inermis ssp. inermis), and orchard grass (Dactylis glomerata).

The sugar maple-American beech-eastern hemlock forest is located within the floodplain of Sawmill Creek.  The open canopy is dominated by immature sugar maple, American beech, and eastern hemlock with black walnut (Juglans nigra) as the associate.  The canopy trees in this community are also greater than 100 years old.

From the perspective of wildlife habitat, this natural area is large and diverse, with several nodes of habitat that have a low edge-to-interior ratio, though it is split into three parts that are separated by busy roads (The Collegeway).  There are 70 bird species, 7 mammals, 3 amphibians and 3 reptiles recorded from this site.  However, during the 2006 field visits the number and diversity of species heard within this natural area was surprisingly low, and almost all species were habitat generalists that utilize a variety of forest and successional habitats within the City, such as northern cardinal, black-capped chickadee and American robin.  The exceptions to this were species such as eastern wood-pewee, eastern screech-owl and several red-eyed vireo, both species specific to intermediate-aged or mature forest habitats.  Three area-sensitive forest species were also noted: white-breasted nuthatch, red-breasted nuthatch and pine warbler (the latter two species specific to coniferous habitat, noted on the hemlock forest slope).  Also adding to the diversity
were a few species of successional habitats such as gray catbird (a Credit Valley Conservation Species of Conservation Concern that is common in Mississauga) and cedar waxwing.  A fox cub was noted within this natural area, indicating that foxes breed at this site.  Several other urban predators were noted, including skunk, raccoon, and a domestic cat (seen in the narrowest portion).  During the spring and fall migration periods, the diversity of birds is expected to increase as species utilize remnant natural areas as stopovers en route to breeding or wintering habitat.  Also, a few species such as snowy owl and common redpoll move south in winter and may utilize natural areas in the City.  This site is extensively used by fauna species throughout the year.  Fish species that utilize Sawmill Creek are common to the credit river watershed.  Sawmill Creek is classified as a type 2 fishery within this site.