Effective implementation of the Natural Heritage Policy requires an understanding of some of the key concepts and ecological factors underlying natural heritage system planning. The text that follows is intended to introduce some of these concepts and factors. This material will help address three fundamental questions in natural heritage system planning:

  1. How do surrounding landscapes affect natural heritage protection needs within a planning area?
  2. How much natural area should be protected within a planning area?
  3. Which are the most important areas to protect within a planning area?

In areas where few natural heritage features and areas remain, or where they are degraded or fragmented, the information provided in this appendix will help determine where improvements (i.e. restoration efforts) would be most effective. This is consistent with Policy 2.3.4 of the Provincial Policy Statement.

Maintaining natural heritage systems

The reasons why natural heritage features and areas need to be protected can be distilled into two key goals:

  • to help conserve biodiversity
  • to ensure that ecosystems/landscapes are both healthy and functional

Achieving these goals is essential to human survival and to ensure that society can continue to derive benefits from natural heritage systems.

Biodiversity

Biodiversity, or biological diversity, is a concept that expresses the variability of life on earth, and the diversity of ecological processes and dependencies that are characteristic of ecosystems (Riley and Mohr 1994). The United Nations Convention on Biodiversity, which was signed by Canada in 1992, defines biodiversity as follows:

Biodiversity is the variability among organisms from all sources including terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part; this includes diversity within species, between species and of ecosystems.

Biodiversity is commonly measured at several levels. Noss and Cooperrider (1994), Decker et al. (1991) and Riley and Mohr (1994) describe four-level systems with the following components: genetic; species/population; community/ecosystem; and landscape/region.

  • Genetic variability refers to the genetic differences that occur within a particular species that can be passed along to offspring. It is the set of traits that allow species to adapt to change over time.
  • Species diversity refers to the variety of species that occur within a particular area. Collectively, all of the individuals of a particular species in a particular area form a population. Management efforts and conservation goals are often directed at populations, or the habitats necessary to sustain them.
  • Community diversity refers to the associations of species within an area. These associations, also called biological communities, are the living components of ecosystems. Ecosystems are composed of two elements:
    1. the biological communities within an area, and
    2. the physical environment within the area.

    In many cases, the most effective way to manage or conserve species or populations is to manage or conserve the communities/ecosystems within which they are found.

  • Landscape/regional diversity refers to the variety of ecosystems and communities that can be found within the landscape. At this scale, the size, arrangement and degree of interconnection between ecosystems/communities are particularly important.

These four biodiversity levels are interdependent. Conserving the biodiversity within a planning area requires that each of these levels be considered. Management/protection actions are often most appropriately undertaken (effectively) at the community/ecosystem level. Planning for natural heritage values, however, often benefits from considerations at the landscape level.

The conservation of species and ecosystems is fundamental to the protection of the province’s, and the planet’s, biodiversity. The need to protect biodiversity is recognised globally. Canada, with the support of provincial and territorial governments, acknowledged this by signing the United Nations Convention on Biodiversity in 1993. Since that time, the Canadian Biodiversity Strategy has been developed, and all provinces have made a commitment to implement it within their respective jurisdictions.

Healthy/functional ecosystems/landscapes

The maintenance of biodiversity, as described above, is of immense importance. However, planning for biodiversity, alone, will not ensure the proper functioning of the underlying ecosystems and landscapes. Additional measures are required in order to ensure the health and proper functioning of the ecosystems in which we live. These measures involve conserving more of the landscape than is required to meet biodiversity objectives alone. Maintaining the health and functionality of ecosystems and landscapes is essential if municipalities are to continue to derive benefits from natural heritage systems.

Key concepts in natural heritage system planning

Important steps in natural heritage system planning are to identify the natural areas within the planning area and to assess their ecological importance. Each candidate site can be evaluated using several criteria since natural heritage features and areas provide many values. However, it is often necessary to rely on a limited number of criteria due to constraints such as budget, time or information.

The following is a discussion of some ecological factors that are commonly incorporated into various natural heritage areas, evaluation procedures. These factors are based largely upon Crins (1996), Decker et al. (1991), Noss and Cooperrider (1994), Phillips (1996), Primack (1993), Riley and Mohr (1994) and Smith and Theberge (1986). Some are illustrated in Figure 1.

Figure B-1: Relative habitat value in relation to patch size, shape, arrangement and function
Rule Good Poor
A. Natural heritage systems that include the full range of habitat-landform types are better than those that contain fewer habitat- landform types. diagram representing a good relative habitat value for rule A. diagram representing a poor relative habitat value for rule A.
B. Large patches are usually better than smaller patches. diagram representing a good relative habitat value for rule B. diagram representing a poor relative habitat value for rule B.
C. Large patches are usually better than clusters of smaller patches with the same total area. diagram representing a good relative habitat value for rule C. diagram representing a poor relative habitat value for rule C.
D. A compact patch with a limited amount of edge is better than a narrow patch with more edge. diagram representing a good relative habitat value for rule D. diagram representing a poor relative habitat value for rule D.
E. Connected patches are usually better than unconnected patches. diagram representing a good relative habitat value for rule E. diagram representing a poor relative habitat value for rule E.
F. Closely clustered patches are usually better than less closely clustered patches. diagram representing a good relative habitat value for rule F. diagram representing a poor relative habitat value for rule F.
G. Clustered patches are usually better than “in-line” patches of the same total area. diagram representing a good relative habitat value for rule G. diagram representing a poor relative habitat value for rule G.
H. Patches that meet several of the habitat needs of one or more species are more valuable than patches that meet fewer habitat needs. diagram representing a good relative habitat value for rule H. diagram representing a poor relative habitat value for rule H.
I. Clusters of patches that collectively meet several of the habitat needs of one or more species are more valuable than clusters of patches that meet fewer habitat needs. diagram representing a good relative habitat value for rule I. diagram representing a poor relative habitat value for rule I.
J. Natural areas that contain more than one natural heritage feature or area may be more valuable than patches with a single natural heritage feature or area. diagram representing a good relative habitat value for rule J. diagram representing a poor relative habitat value for rule J.
K. Clusters of patches that contain several types of natural heritage features or areas are more valuable than areas with clusters of patches composed of a single type of natural heritage area. diagram representing a good relative habitat value for rule K. diagram representing a poor relative habitat value for rule K.
L. Patches that contain a high diversity of species are usually more valuable than patches that contain fewer species. circle with many dots representing many species circle with few dots indicating few species
M. Patches that contain rare species are generally more valuable than patches without rare species. diagram representing a good relative habitat value for rule M. diagram representing a poor relative habitat value for rule M.
N. Patches that are relatively unaffected by human use are more valuable than more disturbed patches. diagram representing a good relative habitat value for rule N. diagram representing a poor relative habitat value for rule N.
O. Patches that contain water- bodies are generally more important than those that do not. diagram representing a good relative habitat value for rule O. diagram representing a poor relative habitat value for rule O.

Representation/distribution

A fundamental step in natural heritage system planning is to ensure that the full range of natural features that occur in an area, including both rare and common features, are protected. The rationale for doing so is to ensure that the full range of species and habitats within those features are protected, thus contributing to the preservation of biodiversity at the species and community levels. Further, species, communities and ecosystems that are well distributed across their native range are less susceptible to decline than species, communities and ecosystems confined to small portions of their historic range (see Figure B - 1A).

Representation is normally assessed at the site district level. It forms the cornerstone of the identification and evaluation procedure for the province’s ANSI program. Planning authorities can make a significant contribution to the protection of the full range of natural features and species that occur in an area by ensuring the protection of any significant ANSIs that have been identified. Representative areas provide a logical foundation around which a planning area’s natural heritage system can be designed.

Rule #1

Ensure that the full range of habitat/landform types that occur in an area are protected.

Size

Large patches of natural areas are generally more valuable than smaller patches (see Figure B - 1B). Similarly, a single large patch is generally better than several smaller patches of the same total area (see Figure B - 1C). There are several reasons.

  1. Larger patches tend to contribute more to biodiversity than smaller patches of similar habitat (Phillips 1996). This is because large areas tend to contain a broader diversity of features and habitats than smaller areas. In doing so, larger areas generally
    • contribute more to the diversity of features in an ecoregion/ecodistrict than smaller areas, and
    • meet more of the habitat requirements of a greater number of species than smaller areas. One of the reasons for this is that large areas generally provide more “interior” (i.e. contiguous, relatively undisturbed, unfragmented) habitat than smaller areas. “Interior” habitat is critical to the survival of many species, particularly “forest-interior” birds.
  2. Larger natural areas are generally more resilient to the impacts of human disturbance. For example, many of the smaller woodlots in southern Ontario contain a large number of invasive exotic plant species that can or have displaced native species. Larger natural areas are more likely to have internal ecosystem functions like nutrient cycles and food webs intact and to be large enough to permit different successional stages to co-exist on the site.
  3. Large areas are capable of supporting larger populations of different species than smaller blocks of similar habitat (Noss and Cooperrider 1994). Large populations tend to be more resilient to human-induced and other disturbances than smaller populations.
  4. Cumulatively, small areas can provide significant benefits to the overall landscape by reducing erosion, providing wildlife habitat, etc. These effects, in turn, benefit other critical habitats.

Are small areas worth keeping? Many small natural areas should be protected. There are several reasons why such areas can be important.

  1. Small areas, particularly if they provide unique habitat conditions, can support rare plant or animal species found nowhere else in the area. Such small areas are particularly important to species with low mobility (Riley and Mohr 1994).
  2. Small areas, particularly if interspersed amongst larger habitat patches, can provide important temporary refuges better enabling more mobile species to move between larger patches.
  3. As well, in highly diverse landscapes, the protection of several smaller habitat patches can provide better representation of a wider range of habitats than a single larger habitat patch (Peterson and Peterson 1991; Riley and Mohr 1994).
Rule 2

Large patches are generally more valuable than small patches.

Rule 3

A single large patch is generally better than clusters of smaller patches with the same total area.

Shape

The shape of natural heritage areas affects their value as wildlife habitat and their resilience to disturbance effects. Round or block-shaped patches contain less “edge” per unit of area than long, narrow patches (see Figure 1D). Edge refers to the area where different habitats (or habitat conditions) meet. For examples, edges occur where woodlots meet open fields, where uplands meet lowlands, along shorelines and fencerows, at the interface between deep water and shallow water, etc. Many species of wildlife (e.g., deer, and grouse) need “edge” habitats.

Other species, however, require large contiguous blocks of habitat well away from habitat edges. These areas are often termed interior habitats. Some interior habitat dwelling species will only use an area if it is 100 metres or more away from an edge.

In parts of Ontario, particularly in the south, the fragmentation of natural habitats has created an abundance of edge habitat while, at the same time, reducing the availability of interior habitats. Consequently, in southern Ontario, round or block-shaped areas would normally be higher priority areas for protection than long, narrow habitats of similar composition. In some situations, however, narrow habitat patches may have special value in ensuring the connection of other important patches.

Rule #4

Patch shapes that minimise “edge” are generally preferred over patches with more edge.

Fragmentation/connectedness

An obvious impact of development on natural areas is fragmentation. Fragmentation refers to the process by which large, interconnected natural areas are converted to a series of smaller, often isolated natural areas. In much of southern Ontario, the landscape has become highly fragmented. In other parts of the province, particularly some northern areas, fragmentation has been less severe.

Rule #5

Avoid fragmenting natural areas.

As indicated above, smaller natural areas generally meet the needs of fewer species of wildlife than larger areas. This results from the fact that the remaining areas may simply be too small to meet the habitat needs of the species that once used the area, and the fact that smaller areas, on average, will contain a lower diversity of habitat conditions than larger areas. Small areas are also more easily damaged by disturbance effects and are less likely to have their functional processes intact.

Another potentially serious consequence of habitat fragmentation is the physical separation, or isolation, of one habitat patch from another. If separation distances are large enough, the movement of plants (i.e. their seeds) and animals from one patch to another can be hindered or prevented. The resultant isolation of one wildlife population from another can:

  • lead to inbreeding which, over time, may reduce the ability of the population to survive; and
  • prevent the recolonization of an area after local extinction

As a general rule, then, interconnected patches of habitat are better than isolated patches (Figure 1E). However, there are exceptions. Some habitats and species that are found in isolated areas are better protected when they are isolated from other areas. Other habitats (and species) do benefit from connections, but only if the connections between them have the appropriate characteristics. For example, very narrow connections, such as fencerows, which link one woodlot to another, can provide predators with an extremely effective hunting environment, which can put prey species at risk. The key is to plan for connections of larger woodlots or a network of smaller areas. In doing so, the widest possible connections should be protected. Where connections are very narrow, planning authorities should consider improving (i.e. widening) them. This is consistent with Section 2.3.3 of the Natural Heritage Features and Areas Policy.

Rule #6

Connected patches are usually better than unconnected patches.

Arrangement/proximity

Blocks of habitats that are arranged close together are usually better than blocks of habitat that are located further apart. There are two reasons for this. First, wildlife is able to move more safely between closely spaced habitat patches than between patches located farther apart. Secondly, closely spaced patches are more likely to have important functional (i.e. hydrological or biochemical) linkages than more distant patches (see Figures B - 1F and G).

Rule #7

Clustered patches are usually better than “in-line” patches of the same total area.

Rule #8

Closely clustered patches are usually better than more distant patches.

Habitat diversity/complexity

Natural areas (or clusters of areas) that span a range of topographic, soil and moisture conditions, tend to contain a wider variety of plant species and plant communities, and may also support a greater diversity of ecological processes, than similar areas that occupy a narrower range of topographic, soil and moisture conditions. Areas with a high diversity of plant species and plant communities will generally support a correspondingly high diversity of animal species and communities. For example, a natural area that includes both wetland (lowland) and upland components will provide a greater range of habitat conditions for wildlife than either habitat type alone. Similarly, a wetland that contains each of the four wetland types (marsh, swamp, bog and fen) will provide more habitat diversity than a wetland composed entirely of marsh (see Figures B - 1H-K). A variety of techniques are available for assessing habitat and/or vegetation community diversity.

Rule #9

Patches, or clusters of patches, that meet several of the habitat needs of one or several species are more valuable than patches that meet fewer habitat needs.

Rule #10

Patches or clusters of patches, that contain more than one natural heritage feature or area may be more valuable than patches with a single natural heritage feature or area.

Species diversity

Areas that contain a high diversity of plant and animal species are generally more important than areas that contain a lower diversity of species (Figure B - 1L). In some situations, however, areas that contain a relatively low diversity of plant and/or animal species are important and should be protected, for example, where they provide habitat for an endangered or threatened species, or some other species of particular interest or conservation concern.

Species richness assessments can be undertaken as a means of comparing species diversity between sites. Species lists compiled in OMNR’s Site District reports or in individual site inventory reports may be useful in conducting such assessments. It is essential to assess diversity relative to each candidate area’s size since the number of species will vary with size.

Rule #11

Patches that contain a high diversity of plant and animal species are generally more valuable than patches with a lower diversity of plant and animal species.

Species rarity

In general, habitats that contain rare species are more valuable than habitats that do not contain such species (Figure B - 1M). Rarity is a relative term and can be described in 5 different ways:

  1. species that are scarce, but occur over a wide geographical area
  2. species that only inhabit one place
  3. species that are geographically separated from their main range
  4. species that are at the edge of their geographical range
  5. declining species that were once more abundant and/or widespread but are now depleted

Assessments of rarity are often expressed as the number of rare species or features in an area. Lists of species and features considered rare at one or several scales (e.g., local, regional, or national), such as those provided in OMNR’s Site District reports or in NHIC’s status lists, will be useful in evaluating candidate natural areas for significance. Specifically, the occurrence of rare species may add to the significance of a particular feature or area. However, it is important to realise that rare species are not necessarily endangered or threatened species, as defined in the policy.

Rule #12

Patches that contain rare species are generally more valuable than patches that do not contain such species.

Naturalness/disturbance

Relatively undisturbed natural areas are generally more desirable than highly altered areas (Figure B - 1N). The manner in which the adjacent lands surrounding a protected natural area are used and/or developed can markedly affect the viability of the natural area or the features within it. The most common rationale for using naturalness as a criterion is that undisturbed, natural areas provide the best source of baseline information to compare with other modified areas. By studying how undisturbed ecosystems function, a better understanding of how human impacts modify ecosystems can be gained. These areas will also provide important clues for restoring ecosystems that have been modified.

Methods used to evaluate naturalness vary depending on the ecosystem, information available and the level of human disturbance. For example, measuring the relative absence of exotic species could assess the naturalness of a valley-land, cattle-grazing or man-made structures such as riprap, dams, roads or buildings.

Rule #13

Patches that are relatively unaffected by human disturbance are generally more valuable than patches that are more highly disturbed.

Hydrologic and related values

In many areas, water bodies including wetlands, often represent a relatively small percentage of the total land area, yet they can be disproportionately more valuable than other areas (Figure B - 1O) for several reasons:

  • there is a large number of aquatic or riparian (moist-area dependent) plant and animal species that depend upon water bodies or wetlands to fulfil their habitat needs
  • there is a large number of other animal species that require access to water bodies for all or part of their life cycle in order to survive
  • there is a large number of species that use water bodies, especially streams, as travel or migration corridors
  • they are critical to the maintenance of nutrient and other bio-chemical nutrient cycling processes upon which all species depend
  • they are integral to the hydrologic functioning of the watershed within which they are located

Water bodies, wetlands, and other areas of significant hydrological importance (i.e. headwaters, recharge areas, discharge areas, etc.) should be protected.

Rule #14

Waterbodies, wetlands and other areas (e.g. seeps, recharge/discharge areas) are very important and should be protected wherever possible.

References cited

  • Crins, W.J. 1996.Life science gap analysis for site district 4E-3. Ontario Ministry of Natural Resources, Lands and Natural Heritage Branch, Peterborough, Ontario. 251 p.
  • Decker, D.J., M.E.. Krasny, G.R. Goff, C.R. Smith and D.W. Gross, editors. 1991. Challenges in the conservation of biological reserves - a practitioner’s guide. Westview Press. 402 pp.
  • Noss, R.F. and A.Y. Cooperrider. 1994. Saving nature's legacy: protecting and restoring biodiversity. Island Press, Washington, DC. 416 p.
  • Peterson, E.B. and N.M. Peterson. 1991. A first approximation of principles and criteria to make Canada’s protected areas system representative of the nation’s ecological diversity. Western Ecological Services Limited, Victoria, British Columbia. Report for the Canadian Council on Ecological Areas. 47 p. + appendices.
  • Phillips, M.E.J. 1996. Natural heritage protection in southern Ontario. Terrestrial ecosystem assessment and management: the case of forested environments. M.Sc. Research Paper. University School of Rural Planning and Development, University of Guelph, Guelph, Ontario. 77 p., Appendices.
  • Primack, R.B. 1993. Essentials of conservation biology. Sinauer Publishing. 564 p.
  • Riley, J.L. and P. Mohr. 1994. The natural heritage of southern Ontario's settled landscapes. A review of conservation and restoration ecology for land-use and landscape planning. Ontario Ministry of Natural Resources, Southern Region, Aurora, Science and Technology Transfer, Technical Report TR-001. 78 pp.
  • Smith, P.G.R and J.A. Theberge 1986. A review of criteria for evaluating natural areas. Environmental Management 10: 715-734