2007 Upper Thames River Watershed Report Cards

• 1.1 Introduction & 1.2 The Process

• 1.3 Water Quality

• 1.4 Forest Conditions (this page)

• 1.5 Watershed Features, Action Plan and Highlights of Progress

• 1.6 References

Back to the 2007 Report Card homepage.

1.4 Forest Conditions

1.4.1 Introduction

Deciduous forests, wetlands, meadows and prairies covered the upper Thames River watershed prior to European settlement. Species diversity was very high in this region due to the long growing season, rich soils and productive waterways. However, these same factors also made the area attractive for farming and urban development. Today, forest cover is highly fragmented, existing as small woodlots separated by agricultural fields, urban development and other land uses.

Forests and other natural areas fulfill many functions, including:

• protecting and building the soil (humus layer),

• producing oxygen and taking up pollutants,

• moderating the climate,

• protecting groundwater,

• providing fuel, timber, seeds and berries,

• providing areas for recreation and education,

• providing habitat for wildlife, and

• contributing to our heritage.

Ecologists and biologists have been studying the health of southern Ontario’s natural landscapes for decades and are concerned about the dwindling amount of natural vegetation and the ability of these habitats to support a healthy diversity of native plants and animals.

“Deforestation is often seen as just a net loss of forest cover. But deforestation can also refer to the loss of quality of the remaining forests. The size and shape of a woodlot affect its quality, as do its proximity and linkage to other landscape features” (Federation of Ontario Naturalists).

To evaluate the health and status of the terrestrial environment, key indicators were used to give a grade to the forest conditions in each watershed of the upper Thames. The indicators, methods and results are described below.

1.4.2 Indicators

As it is impossible to study or inventory every woodlot in a watershed, landscape-scale parameters were used as a means of measuring overall forest conditions. Two indicators were selected: percent forest cover and percent forest interior. Both indicators relay a great deal of information about how sustainable the natural heritage system is and both can be calculated relatively quickly and uniformly across the watersheds using Geographic Information Systems (GIS) technology. Table 5 describes the indicators, how they were calculated and their importance.

Table 5. Description of Forest Conditions Indicators

Indicator	What it measures	How it is calculated	Why it is important
% Forest Cover	The percentage of the watershed that is forested.	Divide the area of forested land by the area of the watershed.	It is believed there should be about 30% forest or natural cover in southern Ontario’s landscape to sustain native plants and animals (Environment Canada, 2004). This percentage is a long-term goal.
% Forest Interior	The percentage of the watershed that is “forest interior.”	Interior is that portion of a woodlot left when a 100 m wide strip is removed from the perimeter. Divide the area of forest interior by the area of the watershed.	The outer 100 m of a forest is considered edge habitat and prone to high predation, nest predation, alien species, damage from sun and wind, etc. Many bird species require large forests to breed successfully. Many forest bird species are declining.

The overall amount of forest cover is of greatest importance in terms of maintaining native plant and animal populations. Forest birds are a good indicator of habitat quality, that is, the ability of habitats to sustain native animals and plants. Environment Canada (2004) recommends 30% forest cover by watershed or area of concern. This threshold is based on the fact that forest bird populations decline in areas with less than 30% forest cover.

In fragmented landscapes with less than 30% forest cover, forest interior plays a major role in determining breeding bird success. Forest interior includes the core of the woodlot, minus the outer 100 metres along the edge. The edge of a forest is more likely to possess non-native plants, the trees are exposed to sun scald and wind throw, and predators (e.g. racoons) are more abundant. Brown-headed cowbirds are the main nest parasites of forest breeding birds and they are more likely to lay their eggs in host bird nests within approximately 100 m of the forest edge (Environment Canada / CWS Factsheet).

Environment Canada (2004) indicates forest interior should be greater than 10% to maintain breeding birds, especially area-sensitive birds. The proportion of the watershed that is forest cover 200 m or further from the forest edge, called deep interior, should be greater than 5%. Area-sensitive forest birds are species requiring a relatively large forest patch within which to reproduce successfully. Many of Ontario’s forest birds, including many migrant raptors and songbirds, are fully or somewhat area-sensitive, being drawn to large forest patches to fulfil breeding needs and to seek protection from nest parasites and other disturbances.

1.4.3 Grading

Table 6 shows the grading system used in the 2007 report cards. This system is based on the provincial grading system (Conservation Ontario, 2003) that was developed in consultation with biologists and conservation authority staff across Ontario. The information from Environment Canada (2004) was not available at the time these scoring grids were developed, but the A’s come reasonably close to the targets described above. The grading varies slightly from the grading used to develop the 2001 watershed report cards.

For the purpose of these report cards, an A is achieved when percentage forest cover or interior reaches a sustainable level, not 100 percent. The grades also reflect the range of conditions across southern Ontario.

Table 6. Forest Conditions Scoring Grid (Provincial Grading System)

% Forest Cover	% Forest Interior	Points	Grade		Final Points	Final Grade*
> 25.6	> 7.7	5	A		> 4.5	A
18.8 - 25.6	5.7 - 7.7	4	B		3.5 – 4.5	B
11.9 - 18.7	3.7 - 5.6	3	C		2.5 – 3.4	C
5.0 - 11.8	1.7 - 3.6	2	D		1.5 – 2.4	D
< 5.0	< 1.7	1	F		< 1.5	F

* Final grade is determined by adding the points for each indicator and dividing by two.

1.4.4 Methodology

The main mapping layer utilized was SOLRIS (Southern Ontario Landuse Resource Information System) from the Ontario Ministry of Natural Resources. SOLRIS is based on 2000 air photography and is in Vector format. Vector format is more accurate at defining the edges of woodlots than Raster format, which was used in the 2001 report cards. The Raster format slightly over-estimates the size of woodlots.

SOLRIS is an improvement over mapping sources used in the past as it defines more habitat types (e.g. some wetlands, windbreaks) but it was still in the draft phase when utilized for this project. A major drawback to SOLRIS is that it dissects woodlots where meadows, creeks, small trails and corridors are present. For example, a woodlot with a creek or meadow running through the middle is carved in two by SOLRIS. The whole woodlot would contain forest interior, but when carved in two, each piece rarely contains interior. This results in an under-reporting of forest interior.

UTRCA staff spent considerable time correcting this problem by re-incorporating the various habitats into continuous woodland polygons. Creeks, meadows, wetlands or even hydro corridors do not present insurmountable barriers to wildlife, and so these features were left inside the woodlot patch. Roads, subdivisions and other urban features do truly dissect habitat and interfere with animal and seed flow and remained as elements that dissect or separate woodland paches. UTRCA staff made several other changes and improvements to the SOLRIS data including the mapping of non-evaluated wetlands and riparian meadows.

Once the vegetation layer was corrected as much as possible, the percent forest cover and interior were calculated using GIS for each of the 28 watersheds within the Upper Thames basin.

1.4.5 Results

• 1.1 Introduction & 1.2 The Process

• 1.3 Water Quality

• 1.4 Forest Conditions (this page)

• 1.5 Watershed Features, Action Plan and Highlights of Progress

• 1.6 References

Back to the 2007 Report Card homepage.

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