INTRODUCTION
The Wilmer Unit of the Columbia Valley National Wildlife Area (NWA), located near Invermere, British Columbia is a 368 ha protected area of dry forests, grasslands, and wetlands managed for critical wildlife habitat and biodiversity. The plant communities within the NWA are fire-adapted and a historical fire regime of frequent low- to mixed-severity fires encouraged open conditions and a complex mosaic of stand structures in upland portions of the NWA. In recognition of the impacts of fire exclusion, the Canadian Wildlife Service (CWS) has identified prescribed burning as an important strategy for building resilience, maintaining biodiversity, and restoring critical habitat for wildlife in the Columbia NWA, which has experienced extensive ingrowth in the absence of fire.
Due to extensive ingrowth associated with fire exclusion, mechanical thinning treatments will be necessary to prepare treatment units prior to burning. Thinning prescriptions will focus on reducing stand density—particularly of smaller size classes and immature trees, pruning low branches to lift canopy base height, and removing understory stems that represent potent ladder fuels. The aim of these treatments will be to create a forest structure that will be less conducive to crown fire, burn with reduced intensity, and facilitate the safe implementation of the prescribed burn(s). These prescriptions will also be designed to emulate historical fires and restore open forest structures associated with a frequent low- to mixed-severity fire regime. Prescribed burning will be utilized as a follow-up treatment to consume fine fuels, reduce seedling densities, and re-invigorate native plant species that are fire-adapted.
An area has been selected based on topographical features conducive to containing a burn, vegetation structure and composition, existing roads, and administrative boundaries. Thinning and burning prescriptions have been developed for CV1, and further considerations are described in the Treatment Description section below. Approximately 20 hectares of the CV1 unit is located within the federal Wilmer property, while the other 18 ha is located on crown provincial land. Environment and Climate Change Canada (ECCC) requires a qualified contractor to conduct thinning treatments on the remaining area requiring thinning within the federal (NWA) portion of the CV1 unit only (8.5 ha).
This Work is meant to improve wildlife habitat in a National Wildlife Area, and fuels control is a side benefit of this Work.
Treatment Description
The CV1 unit is comprised of a mosaic of Douglas-fir/Rocky Mountain juniper woodlands and open grassland patches. Stand densities range from 0 – 4200 stems per hectare, of which an average of greater than 1000 stems/ha are seedlings and saplings. The workload associated with prescriptions will vary considerably within the unit based on current stand densities and surface fuel loading. Figure 1 depicts the CV1 unit and variability in estimated stand densities from forest inventory plot information collected in October, 2019.
Preliminary prescription development suggests an average of approximately 600 stems per hectare will be targeted for removal, with the majority of these stems having a diameter of less than 10 cm. Current surface fuel loads average less than 1 tonne per hectare, and thus the majority of surface debris to be managed during treatment will be that created by thinning and pruning activities.
Prescriptions will focus on the following objectives:
Thin the overstory to mitigate the risk of crown fire and reduce canopy closure to create habitat for wildlife and plant communities dependent on open conditions;
Thin the understory and prune residual trees to reduce the amount of ladder fuels and thereby moderate expected fire intensity and effects during a prescribed burn; and
Reduce the proportion of Rocky Mountain juniper within the site to better reflect the likely species composition that would have existed in the absence of fire exclusion.
