7.4 Maintaining biodiversity - range considerations

Forest stand activities that may impact range biodiversity objectives include:

• Fire suppression and prescribed fire
• Silvicultural systems
• Planting
• Thinning
• Erosion and brush control
• Soil disturbance and road building

The following discussion applies where range objectives for biodiversity have been established in a higher-level plan, or on areas being managed for integrated use, where range biodiversity objectives can be considered in stand level management decisions.

Fire suppression and prescribed fire

Suppression of natural fires has impacted range biodiversity objectives by altering permanent range ecosystems and preventing the development of potential natural communities.

• For example, there are areas of rangeland where forest ingrowth and encroachment are occurring.

Once open parkland with widely spaced trees, these stands are now becoming denser, with shady conditions prevailing, to the detriment of open-growing plant communities.The use of rehabilitation treatments such as underburning in forests is recommended where fire suppression and harvesting practice has led to denser stands with changed composition.Commercial and pre-commercial thinning may be required in order to allow understorey burning. Work on using prescribed fire to re-establish the natural stand structure is under way in some regions.

For more information about fire disturbance, check the references at http://www.env.gov.bc.ca/fia/documents/TERP_eco_rest_guidelines/defgoals/natdisturb.htm

On transitory range, fire suppression may prematurely limit range use and the development of understorey biodiversity, whereas prescribed fire will enhance range use and understorey biodiversity.

• Provide three examples of how fire suppression and prescribed fires can be used in stand level management decisions?

Silvicultural systems

Silvicultural systems on permanent range may affect range biodiversity objectives by creating changes in the post-harvest plant communities. An example is a cutblock which creates a shift in composition to plant species thriving on disturbance.

This change impacts the understorey seral stage objectives by changing the community to an early stage.

In contrast to these dynamics, lighter selection harvesting provides consistent conditions that maintain the potential natural community, thus allowing range seral stage objectives for biodiversity to be met.

On transitory range, forest harvesting generally benefits range use, but may not benefit the development of PNC. An animal's ability to use the cutblocks for forage is dependent on the amount of debris left on site.

• List two examples of how silvicultural systems can be used in stand level management decisions?

Planting

Planting densities on permanent range can impact range biodiversity objectives. Forested areas prior to harvest may have widely spaced, open-grown stands containing a potential natural community understorey. High planting densities will change this plant community to a shade-tolerant, possibly moss-dominated one, as the canopy closes. Lower planting densities and variable planting densities are more likely to recreate (or emulate) natural understorey conditions for biodiversity. On transitory range, lower and variable planting densities may benefit range use by keeping the stand open longer.

• List two examples of how will planting can be used in stand level management decisions?

Thinning

Thinning can impact biodiversity on permanent range when the residue (e.g., spacing slash) covers and shades the plant community. Residue can limit both light and moisture and take many years to decompose, eventually changing the plant community. Mosses may replace the herb-rich potential natural community. Impacts may be avoided by removal of thinned stems. Where residues are slight or stems are removed, range use and understorey biodiversity will generally benefit from the treatment because the stand is opened to more light. A net benefit particularly applies to thinning on transitory range. However, waste residue is also a consideration for accessibility of stands to grazing animals.

• What are three examples of how thinning can be used in stand level management decisions?

Erosion and brush control

Seeding for erosion and brush control can impact range biodiversity objectives by introducing non-native plants into both permanent and transitory range. Use native seed where possible

• How will erosion and brush control be used in stand level management decisions?

Soil disturbance and road building

Disturbing forest soil can impact range biodiversity objectives by allowing the spread of noxious weeds into both permanent and transitory range. These plants threaten biodiversity of native plant communities and forest regeneration. Noxious weeds (listed under the provincial Weed Control Act) typically are introduced species lacking insect predators and plant pathogens that would serve to keep them in check. Noxious weeds listed under the provincial Weed Act include, for example, spotted knapweed, diffuse knapweed and Canada thistle.

The spread of noxious weeds can be limited by revegetating soils as soon as possible after disturbance. Use only certified seed and make sure equipment is cleaned of weed seeds every time it is moved.