Big Picture Methodology
A natural heritage system includes core natural areas,
other significant natural areas and linking
habitat corridors. This often includes potential areas for restoring and enhancing natural
areas and corridors.
The "Big Picture"
natural heritage system for Carolinian Canada was developed to
combine the best
available data on natural features, plants and animals with a
landscape-level ecological approach and state-of-the-art information
management. A multi-agency Technical Committee was struck in 1999 to provide expert
review throughout the analysis.
The Big Picture method generally followed the following
1) Core natural area selection should preferentially
identify intact natural areas with larger
habitat blocks, and regions with high overall percentages of natural
2) Core areas should include viable occurrences of globally rare species
and vegetation community types, and concentrations of rare species and
3) Minimum core natural area size should exceed 200 hectares where possible, with
smaller high-quality areas in areas with lower amounts of natural vegetation
4) Minimum corridor widths should be at least 200 metres plus any adjacent
areas of natural cover. As a result, almost all of the natural heritage system is
currently in natural vegetation cover with the exception of some portions of 200
metre-wide corridors. These latter areas may represent opportunities for
future naturalization. On the ground, it may be important for ecological
reasons to establish functioning corridors more than 200 metres wide. In other situations, it may not be
feasible ecologically or socially.
5) Where possible, more than 30% of the non-urban area of each ecological
district should be identified as part of the natural heritage system.
What are Carolinian Core Natural Areas?
|To identify Carolinian core
natural areas, digital data sets were assembled to show the locations
of natural features including life science Areas of Natural and Scientific
Interest (ANSIs), evaluated wetlands, Carolinian Canada sites, older
growth woodlands, forest cover (click
to see map of forest concentrations), streams, rivers and element
occurrences (rare species and vegetation types; click
to see map of these). These data were converted to a grid of 25
metre by 25 metre units for the entire Carolinian zone (individual
Each feature type was assigned a point value based on its relative ecological
"value". For example, each pixel within a documented older growth forest
received 15 points, whereas all pixels in the path of rivers and streams
received three points. The following variables were assigned scores for
each of the 25m x 25m map unit in the Carolinian zone.
|Land Cover Types from LANDSAT Satellite
imagery (e.g. wetland, forest, agriculture, urban)
||Life Science Areas of Natural and Scientific
||Concentrations of Rare Species
& Rare Vegetation Communities (Element Occurrences) click
to see map of these
||Forest Interior Outlines
||Carolinian Canada Sites
||Forest Interior "Internal" Buffers
|Drainage (30m buffer around rivers, streams and lakes)
||Older Growth Woodlands
||Forest Cover Concentration within 2 and 10km (click
to see map of forest concentrations)
Scores assigned for each of these variables and additional information
on each variable can be viewed
here. Scores for these variables were then summed to create a total
score for each 25x25m pixel. Click here to see a
map of the higher scores across the Carolinian region.
To identify core areas, this map of scores for each 25x25m map
unit needed a minimum value that would result in a system of core
of reasonable extent and configuration. Two values were considered, 11 and 12. Use of a cut-off of 11 would have resulted
in larger core areas, but would include features with low ecological
integrity (e.g., drainage ditches). A cut-off value of 12 points
resulted in representation of over 30% of the ecoregion in cores,
with fewer patches of low integrity.
Clusters of adjacent 25 metre by 25 metre map units with values
12 or greater were grouped. Any group larger than 200 ha was automatically
considered a "core area". Core natural areas over 200 ha were concentrated
mainly in areas with higher percentage natural vegetation cover.
of the study area had no core areas larger than 200 ha. In
such areas, the OMNR-recommended minimum size for a "significant woodland"
was used, based on percentage forest cover by township, 40 hectares where cover
is 15-30%, and 4 hectares where cover is less than 15%. As a result,
in some townships, core natural areas were as small as 4 ha.
Other Significant Natural Areas were identified
as natural areas with 12 or more points and larger than the minimum area
for significant woodland in each township (i.e. 40 hectares where cover
is 15-30%, and 4 hectares where cover is less than 15%). These are
another important component of the natural heritage system.
What are Potential Habitat Corridors?
The best potential habitat corridors to connect the
system of Carolinian core natural
areas were also identified using the best available ecological inventory
data, a landscape-level ecological approach and state-of-the-art
information technology. This approach used an algorithm to find the best ecological
corridor for the "least cost".
To determine the best potential connections between the core natural
areas, additional data on each 25mx25m portion of the Carolinian zone was
added including variables which would encourage facilitate connection paths between the
core areas ("Linkages") and some which discourage ("Barriers")
connections between the core areas. Recreational Class Provincial Parks,
for example, would make good potential additions to the connections network,
but connections across divided highways would be unlikely. The variables
used are listed below:
- Urban areas
- Extraction sites
- Abandoned pits and quarries
- Utility Corridors
- Abandoned railways
- Agreement forests
- Recreational Provincial Parks
- Regenerating fields
Each value for each of these variables was assigned a score. The "barrier"
scores were negative and the "linkages" variable scores were
positive. For example industrial zoning was assigned a score of -10 while
greenspace zoning was assigned a score of +5. Click
here to see the scores assigned to each variable. An overall
score was determined by adding together the scores for these variables
for each 25m x 25m map unit in the region. The composite scores formed
a "resistance" layer to determine the "least-cost" (i.e. greatest ecological
value with fewest practical obstacles) connections between core natural
These least-cost corridor alignments generally follow existing areas of natural
vegetation cover, especially riparian areas, because of the positive score
values. Where no such alignments along positive values
could occur, the cores were connected along the "highest value per unit
length" route (i.e., in areas without natural vegetation cover), and a minimum width
of 200 metres was assigned to that highest-probability corridor
areas are the only significant part of the mapped natural heritage system
not currently in natural cover.
The general goal was to connect all core natural areas within 20 kilometres of each other.
The minimum score of the least-cost connection between two core natural
areas furthest apart was calculated, and this figure was used as the maximum
cost to form a path between any two core natural areas. This ensured that
all core natural areas were linked to at least one other core area, and
often to many more where there was a high density of core areas and natural
values. These connections were widened to incorporate adjacent natural
areas having a score greater than 12.
All connections were reviewed visually to supplement the digital analysis
which could not make judgements about including or
excluding adjacent natural features, ensure that recreational provincial parks
were included in
the natural heritage system wherever practical and ensure that each
connection follows an ecologically and practically optimal route at
least 200 metres in width.
Not all connections achieved the targeted minimum width of 200 m. Connections
that narrowed to less than 200 m were highlighted as potential
Want more background on the methodology used to develop the
Big Picture? Click here!
NHIC and MNR expanded
the Big Picture to other parts of Ontario in 2002. Click
to get more information on the Big Picture 2002.
Nature Conservancy of Canada has used the Big Picture
as a basis for Conservation Blueprints to guide protection of significant