[Biodiversity Guidebook Table of Contents]
Important stand attributes
To maintain or restore biodiversity in managed stands, some or all of the following attributes should be present. Table A5.1 shows how biodiversity attributes interact with management activities.
Many organisms depend on the natural decay cycle. Decaying wood, for example, provides habitat for numerous vertebrates, fungi, invertebrates, lichens, plants and micro-organisms. Dead wood also plays an important role in nutrient cycling. Standing dead trees (snags) and fallen logs (coarse woody debris) are important to retain, as are dying trees, which provide a source of future snags and downed logs.
Standing dead trees
Standing dead trees provide nesting and foraging habitat for a wide range of species. Providing snags in managed forests is probably the most important stand management practice to maintain biodiversity. Some existing snags should be retained, but equally important is ensuring that new snags will be recruited into the stand in the future. Small diameter snags are adequate for some species, while large diameter snags are required by other species and endure longer.
In order to maintain desired stand-level characteristics into the future, it is important to work with the attributes already present in each stand. In other words, habitat that is considered valuable for the maintenance and recruitment of standing dead trees should be assessed on a block-by-block basis, preferably during pre-harvest planning and development stages. Where no wildlife tree patches are planned within a particular block because of adequate representation nearby (for example, sufficient habitat representatives of that ecosystem exist within the wildlife tree reserve planning unit or in other leave strategies such as FENs), then specific high value habitat features that may be present on the block (such as eagle trees, largest live culls, or large snags along riparian areas) should be identified and retained where it is safe to do so. In general terms, lower numbers of suitable large-diameter standing dead trees are required within each harvest block if the FEN or other landscape leave strategy is able to provide this habitat across the planning unit, both currently and into the future. However, if few standing dead trees are present within the surrounding landscape, then the supply needs to come increasingly from harvest blocks at the stand level.
Techniques to maintain an adequate number of snags and provide future snags in managed stands include:
- retaining some snags during harvesting where it is safe to do so (within wildlife tree reserve areas and along block boundaries)
- retaining some live trees during harvesting as a source of large-diameter snags in the subsequent rotation
- promoting a deciduous component in the stand as a source of snags
- retaining snags during spacing and thinning (where it is safe to do so)
- creating snags. More specific information on snags can be found in Wildlife/Danger Tree Assessorís
Coarse woody debris
Decaying logs on the forest floor provide cover, micro-climates, and breeding habitat for a wide variety of organisms. Woody debris should be retained in the stand when utilization standards are being applied and site preparation treatments undertaken. Larger size pieces are preferable, as they provide the greatest longevity and potential for nutrient cycling and wildlife use in the second-growth forests. Coarse woody debris is rarely evenly distributed, but it should be as well distributed as possible throughout the block.
Large living trees
Large, old living trees provide several unique habitat attributes and should be retained. For example, large mossy limbs provide marbled murrelet nest sites and a habitat for a variety of invertebrates. Arboreal lichens and other epiphytes are most abundant in older trees. Large living trees also provide a source of future snags.
Such trees can be retained through a variety of silvicultural systems and harvesting activities. For example, wildlife tree patches established to maintain snags are also good areas for retaining large living trees.
Tree species diversity
An ecologically appropriate variety of tree species, including hardwoods, should be retained in a stand. Such diversity can meet the habitat requirements for a greater variety of organisms than could be met in a homogeneous stand.
Tree species composition can be managed by choice of silvicultural system, harvesting, site preparation, planting, regeneration, and stand tending activities.
An important attribute for maintaining biological diversity is a variety of canopy layers (vertical structure) and spatial patchiness (horizontal structure). This variety of layers includes the naturally occurring forest understorey of shrubs and forbs, which provide food and cover for numerous species. To maintain understorey vegetation, a partially open or patchy forest canopy is required. Structural variety creates more habitat and micro-climate diversity than homogeneous stands.
Vertical and horizontal structural diversity can be maintained or created by choice of silvicultural system, harvesting methods, and stand tending activities. Even-aged systems tend to create structural variety between stands that are at different seral stages, whereas uneven-aged systems tend to create structural variation within single stands. With either method, structural variety changes as forests grow.
Soil management has a major effect on the ecological characteristics and degree of biodiversity of any given stand. Soil structure, nutrient spectrum, organic matter content, water retention and drainage, and pH play a major role in determining the vegetative composition of ecosystems. Maintaining the full range of soil conditions and humus forms on the landscape is a prerequisite for the development and maintenance of a diverse flora and fauna.
Forest practices that minimize soil disturbance are the best way to maintain the below-ground biodiversity and ensure the continued functioning of the soil ecosystem.
Table A5.1. Interaction of management activities and biodiversity attributes
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