[Biodiversity Guidebook Table of Contents]
Designing forest ecosystem networks
This section provides planners with direction in designing landscape units that meet old-growth and connectivity objectives while minimizing negative impacts on timber and range resource values. The recommended long-term landscape management approach is that of creating forest ecosystem networks (FENs) within the landscape units.
A FEN is a contiguous network of representative old-growth and mature forests (some of which provide forest interior habitat conditions) delineated in a managed landscape. Not only does a FEN aim to meet the needs of native species and ecological processes, it also serves to maintain or restore the natural connectivity within a landscape unit.
FENs are composed of a variety of protected areas, as well as classified areas (such as riparian management areas and wildlife habitat areas), any other areas that have been designated as sensitive, high visual quality areas, and areas of unstable terrain or other conditions that make them inoperable.
Most landscapes already contain significant areas within which timber harvesting is constrained. FENs should therefore be designed to take advantage of these areas, using them to form the network “building blocks.” This approach makes efficient use of the land base by allowing existing areas with harvesting constraints to serve the dual purpose of protecting a particular resource value while also contributing to the overall structure and composition of the FEN.
In mountain and valley ecosystems with wet climates, where contiguous old-growth forest was a dominant component of the natural landscapes, the delineation of FENs is especially important. However, FENs may also be used in other ecosystems to link important habitats such as wetlands. At the same time, not all components need to be connected and, overall, the need for connectivity varies among disturbance types.
Forest ecosystem networks provide the following benefits:
Several general considerations in FEN design are:
- They reduce the impact on landscape units of habitat fragmentation and old-growth conversion.
- They represent the full range of ecosystems in the landscape unit.
- They provide some forest interior habitat within each landscape unit.
- They provide wildlife species with areas of refuge during periods of disturbance on nearby sites, as well as acting as centers and corridors of dispersal for the re-colonization of historic ranges by certain species.
- They provide a continuum of relatively undisturbed habitat for indigenous species that depend on mature and old-growth forests.
- They provide daily and seasonal movement corridors for certain species.
Figures 6 and 7 illustrate how a landscape unit incorporating FENs, might be managed to maintain biodiversity.
- Some components of a FEN should be permanent reserves (for example, unstable slopes); others should be sensitive areas that retain important stand attributes (for example, riparian management areas).
- Riparian habitats (found adjacent to streams, rivers, lakes, and wetlands) provide many of the features necessary to maintain biodiversity at the landscape level. In many instances these should form the focal point in FEN delineation. Their linear nature provides species with movement opportunities between ranges at different altitudes, and their diverse vegetation provides species with the structural and functional attributes they need to be sustained. Nevertheless, while riparian areas are important to most species, FENs should not be composed entirely of riparian habitats.
- Where areas previously constrained (such as wildlife habitat areas, riparian management areas, areas with visual quality objectives) are used to meet old seral requirements, they will henceforth be managed as old-growth management areas.
- It is important that all ecosystems in a landscape unit be represented in the FEN designed for that unit. This means that upland habitats such as those on south aspect slopes and ridge tops, as well as habitats on cooler and moister northerly aspects, should be considered.
- A key component of FENs is, as the name implies, the requirement for important habitat features to be connected in a manner that forms a comprehensive landscape network. Ideally, this connectivity should be dominated by old-growth or mature timber and should be established to incorporate natural terrain features such as gullies and ridges. As shown in each of the five disturbance type summaries, the characteristics of natural connectivity vary by NDT (see “Landscape connectivity” under each disturbance type summary).
- In designing FENs for any one landscape unit, planners should remember to consider the habitat conditions and management plans in adjacent landscape units, as these may affect issues of connectivity and age class distribution in the unit being designed (see Appendix 2).
Principal steps in designing a FEN
- dentify and map representative and rare old-growth stands:
- Establish a list of representative and rare ecosystems using site series or other mappable surrogates such as forest cover and soils/terrain maps.
- Map the location and extent of rare and representative ecosystems.
- Assess which forested habitats are of sufficient size to provide forest interior stand conditions.
- Identify and map the forest areas that will not be harvested. Determine the extent to which they can meet old-growth retention objectives for rare and representative ecosystems.
A. Existing protected areas
B. Ecological reserves and wilderness areas
C. Areas subject to harvesting constraints:
D. Inoperable areas
- – riparian management areas
- – lake shore management areas
- – wildlife habitat areas
- – terrain sensitive areas
- – recreation areas
- – visually sensitive areas.
E. Areas that provide habitat for threatened or endangered species (contact the Conservation Data Centre for information)
- Assess the complex of areas identified above and list representative and rare ecosystems not protected as potential old-growth management areas.
Figure 6. A landscape managed to maintain biodiversity.
Figure 7. A portion of the landscape managed to maintain biodiversity.
- Where old-growth retention or representativeness objectives have not been achieved, create old-growth management areas (OGMAs) between the mapped areas.
- Ensure that OGMAs are composed mainly of old-growth or mature forest. Use existing forests as models when considering the appropriate appearances of OGMAs.
- Where second-growth forests must be used, consider applying silvicultural interventions to develop and enhance mature forest attributes (see Appendix 5). The objective is to provide these attributes in levels that meet the natural levels found on similar sites. Site productivity may be a factor influencing the ability of a stand to provide and sustain mature and old-growth attributes more quickly.
- Distribute OGMAs among the low-, mid-, and high-elevation areas within each landscape.
- Narrow OGMAs (less than 600 m) may include small linear landscape features such as gullies, ridges, or streams. Wide OGMAs (greater than 600 m) will provide forest interior conditions. Consider delineating wide OGMAs if such conditions are otherwise absent from the FEN.
- Consider using riparian areas for a portion of an OGMA.
- If there are relatively small gaps between mapped areas within a FEN, fill these in with OGMAs to aggregate the gaps into larger units.
- Recognize that not all areas of harvesting constraint need to be linked.
- Assess whether connectivity objectives have been achieved. If connectivity objectives were not achieved through retention or representation, use mature and old-growth forest in OGMAs to link stands.
- Review the resultant FEN with respect to the biodiversity objectives for the landscape unit and check that, within the FEN:
- all old-growth ecosystems, as represented by site series or a surrogate, are represented at the minimum level specified in the appropriate seral stage tables in the section on “Establishing landscape unit biodiversity objectives”
- rare ecosystems are over-represented
- forest interior condition requirements are met
- connectivity needs are met.
Old-growth management areas
- OGMAs are intended to capture old growth within landscape units to meet retention objectives.
- Timber harvesting and silvicultural practices within an OGMA should be consistent with management objectives for the OGMA.
- OGMAs can be harvested when equivalent old seral stage areas are available.
- Replacement OGMAs can be brought on stream earlier than would naturally occur through silvicultural interventions designed to promote the key attributes, or through the retention of these attributes during harvesting.
Management within FENs
- Roads through protected areas, wildlife habitat areas, and sensitive areas within FENs should be avoided.
- The number, length and width of rights-of-way for roads through FENs should be minimized.
- Prompt and appropriate steps should be taken to deactivate roads no longer in use in FENs.
- Where mature and old seral areas (but not areas designated as OGMAs) are identified to meet connectivity objectives, and provided the connectivity objectives can be maintained, some harvesting can occur within these linkage areas as long as the mature stand attributes are maintained (see Appendix 5).
- When natural disturbances such as wildfire, windthrow, or insect outbreak occur within, or threaten to enter, a FEN, the appropriate management action should be based on an evaluation of the disturbance’s effect on the functioning of the FEN. Conversely, when a natural disturbance threatens to affect areas outside the FEN, the appropriate management action should be based on an evaluation of the impact on the adjacent commercial forest or leave areas.
- Where natural disturbances have affected a FEN, management actions such as salvage logging and site rehabilitation must be evaluated (to determine, for example, the value of the FEN and the value of the damaged timber) to ensure that such decisions do not compromise the integrity of the FEN, adjacent commercial forests, leave areas, or other forest values.
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