City of Mississauga Natural Areas Survey (2015)
Natural Areas Fact Sheet
NATURAL AREA NAME
AREA (HA)
UTM GRID REFERENCE
CRR4
25.28
6047 48256
1. LOCATION
North along the Credit River from the Canadian Pacific Railway line to Bristol Road West. Throughout
its length the Credit River links a number of natural areas, including CRR3, CRR6, and CRR8. The
natural areas CE12 and SV12 are located within 500 m to the west of this site.
2. CLASSIFICATION
Significant Natural Area
3. DESCRIPTION
A. Physical Features
The topography of this site varies between undulating floodplain and steep valley slope (25 to 45%). The
soil type is well-drained Oneida clay loam developed within Halton till. There is an outcrop of the grey
shales of the Georgian Bay Formation, within the site.
B. Biota
There are 160 floral species and 52 faunal species documented for this site. Eight vegetation communities
are present at this site (see accompanying figure); fresh-moist black walnut lowland deciduous forest type
(FOD7-4), dry-fresh sugar maple deciduous forest type (FOD5-1), dry-fresh deciduous forest ecosite
(FOD4), dry-moist old field meadow type/mineral cultural woodland ecosite (CUM1-1/CUW1), dry-moist
old field meadow type (CUM1-1), cattail mineral shallow marsh (MAS 2-1), open aquatic (OAO), and a
manicured area.
Fresh-moist Black Walnut Lowland Deciduous Forest Type (FOD7-4)
The floodplain (FOD7-4 with open inclusions of Black Walnut, Manitoba Maple, and CUM/MAM below)
has an open canopy of Black Walnut (Juglans nigra) with the occasional Manitoba Maple (Acer negundo),
Crack Willow (Salix fragilis), and Cottonwood (Populus deltoides). The canopy covers 60-70% of the
community and is 10-25m in height. The sub-canopy primarily consists of Manitoba Maple, Riverbank
Grape (Vitis riparia), and Green Ash (Fraxinus pennsylvanica), European Buckthorn (Rhamnus
cathartica), Red Maple (Acer rubrum) and American Elm (Ulmus americana) are common associates.
Dense pockets of Red-osier Dogwood (Cornus stolonifera), Riverbank Grape (Vitis riparia), and Staghorn
Sumac (Rhus typhina) occur in the understory (1-2 m and > 60% cover). The ground layer (0.2-0.5 m and
> 60% cover) is a diverse mixture of old field species and wetland species. Common species include
Climbing Nightshade (Solanum dulcamara), Spotted Water-hemlock (Cicuta maculata), Spotted Jewelweed (Impatiens capensis), Annual Ragweed (Ambrosia artemisiifolia), Canada Goldenrod (Solidago
canadensis), Spotted Joe-pye-weed (Eupatorium maculatum ssp. maculatum), Red Raspberry (Rubus
idaeus ssp. melanolasius), and Jerusalem Artichoke (Helianthus tuberosus). Scattered along the river
edge are pockets of Cattail (Typha spp.) and Purple Loosestrife (Lythrum salicaria).
Dry-fresh Sugar Maple Deciduous Forest Type (FOD5-1)
The wooded slope community has a species composition that varies depending on the microclimate, and is
characterized by Sugar Maple (Acer saccharum ssp. saccharum), Norway Maple (Acer platanoides), Red
Oak (Quercus rubra), White Oak (Q. alba), White Pine (Pinus strobus), and Eastern Hemlock (Tsuga
canadensis). For example, in a cooler microclimate, usually associated with north-facing slopes, the
conifers become more prevalent. Sub-canopy (2-10 m and > 60% cover) species include Sugar Maple,
B. Biota continued...
White Ash, American Beech (Fagus grandifolia), and Black Cherry (Prunus serotina). The understory is
dominated by Choke Cherry (Prunus virginiana) which covers 25-60% of the community and grows 1-2
m in height. The ground layer (0.2-0.5 m and > 60% cover) is diverse with species such as Yellow Avens
(Geum aleppicum) and Inserted Virginia Creeper (Parthenocissus vitacea), however, Garlic Mustard
(Alliaria petiolata) is beginning to dominate the ground layer in many locations.
Dry-Fresh Deciduous Forest Ecosite (FOD4)
The floodplain has an open canopy composed primarily of Manitoba Maple, with the occasional Siberian
Elm (Ulmus pumila), Black Walnut, and Crack Willow. Red Maple (Acer rubrum) and American Elm are
common associates. The canopy (10-25m) vegetation covers approximately 60-70% of the community.
The sub-canopy (2-10 m and > 60% cover) consists primarily of Manitoba Maple and Staghorn Sumac.
The understory (1-2 m) is less dense than the canopy layers, with only 25-60% cover. The predominant
species in the understory include European Buckthorn, Riverbank Grape, and Inserted Virginia Creeper.
The ground layer is a diverse mixture of old field species and wetland species (0.2-0.5 m and > 60%
cover). Common species include Crown-vetch (Coronilla varia), Climbing Nightshade, Spotted Waterhemlock, Spotted Jewel-weed, Annual Ragweed, Canada Goldenrod, and Red Raspberry. Scattered along
the river edge are pockets of Cattail (Typha spp.) and Purple Loosestrife (Lythrum salicaria).
Dry-Moist Old Field Meadow Type/Mineral Cultural Woodland Ecosite (CUM1-1/CUW1)
There was a manicured community located within the floodplain of the Credit River within the northern
half of the site which included picnic areas, parking, and play grounds present in this area. However, due
to naturalization efforts undertaken by the City a portion of this community was reclassified as old field in
2002 and has since been reclassified as old field meadow/cultural woodland since 2011. The canopy (1025 m) of this community is sparsely vegetated with Cottonwood which covers 10-25% of the community.
The sub-canopy (2-10 m) is also sparsely vegetated with trees covering 25-30% of the community. Subcanopy trees include Cottonwood, Manitoba Maple, Sugar Maple, and American Elm. The understory
consists of a variety of species including Jerusalem Artichoke, White Spruce (Picea glauca), and
European Buckthorn. Wild Parsnip (Pastinaca sativa), a non-native photo-toxic species, is located
occasionally along the banks of the Credit River. The understory is densely vegetated with > 60% cover
and this vegetation is 1-2m in height. The ground layer (0.2-0.5 m and > 60% cover) contains a variety of
old field and wetland species including Canada Goldenrod, Crown-vetch, Tufted Vetch (Vicia cracca),
Meadow Timothy (Phleum pratensis), Orchard Grass (Dactylis glomerata), Wild Carrot (Daucus carota),
and Common Burdock (Arctium minus ssp. minus).
Dry-Moist Old Field Meadow Type (CUM1-1)
The old field cultural meadow community at the south end of this site is of similar composition to the
understory and ground layers of the CUM1-1/CUW1 community described above.
Cattail Mineral Shallow Marsh (MAS 2-1)
A small island within the Credit River contains a cattail shallow marsh community. This community is
primarily vegetated with Broad-leaved Cattail (Typha latifolia) growing 1-2 m in height and covers > 60%
of the understory. Also occasionally growing within this community is Spotted Joe-pye-weed, Purple
Loosestrife, and Devils Beggar-ticks (Bidens frondosa) in the ground layer (0.5-1 m and 25-60% cover).
Above this layer of vegetation is a sparse canopy (10-25 m and < 10% cover) of Cottonwood.
Open Aquatic (OAO)
The open aquatic community refers to the Credit River; this community contains no vegetation.
B. Biota continued...
Manicured Area
This area remains manicured within the dry-moist old field meadow type/mineral cultural woodland
ecosite.
Fauna typically found in the City’s natural areas are fairly tolerant of urban and suburban conditions. 41
bird species, 4 mammals, 2 amphibians, and 5 reptiles are documented from this site. Bird species which
are adaptable to urban forests are present at this natural area including: Eastern Wood-pewee, Northern
Flicker, Downy Woodpecker, and Red-eyed Vireo. There are also species which are common in riparian
areas such as Warbling Vireo, Belted Kingfisher, Spotted Sandpiper, and Red-winged Blackbird. Less
common species found within the open vegetation communities within this natural area include Bank
Swallow, Tree Swallow, Rose-breasted Grosbeak, and Northern Mockingbird. This is an important area
for nesting, migrating, and wintering bird species. Mammals documented from this natural area include:
Eastern Cottontail, Woodchuck, Gray Squirrel, and White-tailed Deer. There is a White-tailed Deer herd
resident within the Credit River valley. Eastern American Toad and Green Frog have been documented
from this site. Five reptile species have been documented from CRR4: Common Snapping Turtle, Eastern
Milksnake, Northern Watersnake, Brown Snake, and Eastern Garter Snake. The Credit River is an
important waterway for migrating Salmon and other fish species such as Coho Salmon, Chinook Salmon,
and Smallmouth Bass. The Credit River is classified as a type 1 fishery within this site.
4. CONDITION
This site is currently in good condition, with the exception of the manicured area. Disturbances present
include erosion where the Credit encroaches upon valley walls, formal and unplanned trails, noise from
nearby roads as well as airplanes overhead, odours from the sewage treatment plant, soil compaction,
trampling, and Emerald Ash Borer. The invasive plant species Garlic Mustard and European Buckthorn
are present at this site. Also, the non-native photo-toxic wild parsnip is present within the floodplain of
the Credit River at this site. 66 introduced plant species are present at this site (representing 41.25% of the
total number of species present). The native FQI is 34.73 and the native mean coefficient is 3.58, both of
which are medium values. The FQI and native mean coefficient have both increased from the previous
values in 2011 of 33.06 and 3.19, respectively. Surrounding land use is residential and industrial.
5. SIGNIFICANCE
 Black-crowned Night-heron (Nycticorax nycticorax) is considered rare within the province by the
NHIC and is documented as a resident bird species from this site.
 Eastern Milk Snake (Lampropeltis triangulum ssp. triangulum) and Common Snapping Turtle
(Chelydra serpentina serpentina) considered a “species at risk” within the province (COSSARO) and
nationally (COSEWIC) is documented from this site.
 2 plant species considered rare within the City (known from 3 or fewer locations) are documented at
this site; Twinleaf (Jeffersonia diphylla) and Shrubby Cinquefoil (Potentilla fruticosa ssp. floribunda).
 2 plant species considered uncommon within the City (known from 4 to 10 locations) are documented
from this site: Straw-colored Cyperus (Cyperus strigosus) and Wild Blue Phlox (Phlox divaricata).
 31 Credit Valley Conservation flora Species of Conservation Concern (Tier 1-3).
 29 Credit Valley Conservation fauna Species of Conservation Concern (Tier 1-3) including; 21 birds, 2
mammals, 2 amphibians, and 4 reptiles.
 This site is recognized as a migration corridor for birds and animals.
 This site is designated as an Environmentally Significant Area (Credit River floodplain at the Reed
Dam) and provincial earth science Area of Natural and Scientific Interest (Credit River at Streetsville).
 This site is part of the Credit River system which comprises the main natural corridor in the City,
stretching from Lake Ontario to the northern boundary of the City and beyond.
5. SIGNIFICANCE continued…
 Close proximity to natural areas CE12 and SV12.
 Large size (25.28 ha).
 High diversity of vegetation communities (8 communities).
 Floodplain provides floodwater storage for the Credit River.
6. MANAGEMENT NEEDS
 Additional protection should be provided to this site (e.g., signage as part of a large educational
campaign to increase awareness of the site, plus additional management activities).
 Wild Parsnip (Pastinaca sativa), a non-native photo-toxic species, is a human health risk and should
be managed in areas where there is a possibility of human contact.
7. PRINCIPLE REFERENCES
Ecologistics Limited (1979)
City of Mississauga (1978)
North-South Environmental (2001)
Ontario Ministry of Natural Resources (1983)