A wetland is a swamp, marsh, or other similar area that supports natural vegetation that is distinct from the adjacent upland areas. More specifically, a wetland is an area where a water table is at, near, or above the surface or where soils are water-saturated for a sufficient length of time that excess water and resulting low oxygen levels are principal determinants of vegetation and soil development.
Wetlands must have both:
To be considered hydrophytic, the vegetation should include shrub or herbaceous species that occur only on organic soils or soils that are water-saturated for a major portion of the growing season. These species should make up 20 per cent or more of the combined cover of low (<2 m) shrub and herbaceous vegetation. Most (>80 per cent) of the remaining vegetation should be species that are able to establish and grow on water-saturated soils, even though they may not be restricted to these soils. Wetlands may or may not be treed, but when trees are present, the canopy is generally relatively open (<15 per cent canopy closure of trees >12.5 cm DBH), growth rates are much reduced compared to those on the surrounding better drained uplands, and the soil surface is usually hummocky. Wetlands may have up to 2 m of standing water.
Wetlands include shallow open water, swamps, marshes, fens, and bogs (see Appendix 1). In addition, shrub-carrs are included here as wetlands due to their close similarity to and association with wetlands. Shrub-carrs occur primarily in broad depressions and low-lying areas where forest development is limited by cold, periodically saturated soils. The water table is usually well below 30 cm during most of the growing season and the soils are usually not saturated for a sufficiently long period of time to show signs of saturation within 30 cm of the surface. Shrub-carrs are characterized by shrub-dominated vegetation (primarily scrub birch and willows) up to 2 m tall, often with widely scattered, taller trees. They do not include shrub-dominated sites from which a forest canopy has been removed by harvesting, wildfire, or other disturbances or shrub-dominated seepage slopes, such as Sitka alder slopes in the interior, which do not meet the above definition of wetlands.
There are five riparian classes of wetlands (W1 to W5) based on:
W1 to W4 wetlands are simple wetlands while W5 is a wetland complex. A key to riparian classification of wetlands is illustrated in Figure 12.
Simple wetlands include all classified wetlands that are not wetland complexes.
A wetland complex consists of two or more individual wetlands with overlapping riparian management areas and a combined wetland area of 5 ha or more. Two wetlands have overlapping riparian management areas if they are:
The individual wetlands of a wetland complex should be sufficiently large that they would otherwise be classed as W1, W2, W3, or W4. Wetland complexes have a riparian class of W5.
Wetland complexes (see Figure 13) are areas of wetland and upland terrain where wildlife and biodiversity values of RMAs adjacent to individual wetlands are enhanced due to the close proximity to other wetlands. The RMA separating two or more closely associated wetlands provides a frequent travel corridor between the individual wetlands and links them into a larger wetland habitat unit. Forest practices adjacent to these wetlands are especially challenging due to their complexity and value. To address this challenge, some flexibility has been designed into the management practices adjacent to wetland complexes as outlined in "Modifying the RMA."
Since the outer edge of wetlands is often treed, it may not be possible to determine the wetland boundary, and thus wetland area, directly from forest inventory maps. Wetland boundary can be interpreted from 1:20 000 or larger scale stereoscopic aerial photographs or determined by on-the-ground surveys.
The outer boundary of a wetland can be closely approximated from 1:20 000 or larger scale aerial photographs, by noting where:
The wetland boundary can be determined from on-the-ground surveys by mapping the upslope extent of the following combination of conditions:
Biogeoclimatic unit (zone, subzone, and variant) can be determined from biogeoclimatic maps and biogeoclimatic ecosystem classification field guides prepared by the Ministry of Forests, Research Branch.
In addition to the five wetland riparian classes there is a modifier to large W1 and W5 wetlands that does affect the application of the RMA.
These wetlands are a category of very large ( >1000 ha) W1 and W5 wetlands in which the landscape is dominated by (>50 per cent) sphagnum wetlands (bogs including muskeg terrain). They occur in the boreal, parts of the sub-boreal, and hypermaritime climates. In these circumstances, wetlands are not restricted to depressions and the toe of slopes, but can occur on raised areas and sideslopes as well. There is no reserve or management zone required around the outer perimeter of these wetlands. However, where wildlife values or biodiversity concerns warrant, a reserve or management zone may be established by the district manager on patches of upland forest within these wetlands.
Where large contiguous wetlands (>500 ha) occur as significant linear landscape features adjacent to streams, the district manager, with the agreement of a designated environment official, may exempt the requirement for a riparian reserve around the outer edge of the wetland.
Table 2 shows the specified slope distance of the reserve zone and management zone of each wetland RMA class.
In all cases the reserve zone extends from the outer edge of the wetland to the slope distance specified in Table 2 as shown in Figure 14. The management zone extends from the outer edge of the reserve zone or the outer edge of the wetland, where no reserve zone is required, to the specified slope distance.
The outer RMA boundary of the reserve zone and management zone around wetland complexes is determined by the slope distances in Table 2 measured from the outer edge of each of the outermost wetlands of the complex (Figure 15).
Where a reserve or management zone is established by the district manager, the RMA should reflect the landscape level management strategy as outlined in the Biodiversity Guidebook.