Forest Investment Account (FIA) - Forest Science Program
FIA Project Y081268

    Harvesting and site preparation treatments to develop and maintain open canopy conditions in dry-belt Douglas-fir forests: the Isobel Project
Project lead: Klenner, Walt (BC Ministry of Forests and Range)
Author: Klenner, Walt
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
In western North America, forests of Ponderosa pine or Douglas-fir as pure stands or mixtures with other species such as larch, grand fir or lodgepole pine are widespread from Mexico to southern British Columbia. Over the past 50 years, numerous reports have examined and debated the role of fire and fire suppression in these ecosystems (Leopold 1924, Cooper 1960, 1961, Covington and Moore 1994). In the last decade, there has been an increasing concern regarding the shortcomings associated with current fire suppression activities (Daigle 1996, Gayton 1996), and this is being reflected in local Land and Resource Management Planning documents (e.g. see drafts of the Okanagan-Shuswap and Lillooet LRMP). These documents accept the hypothesis that frequent, low severity fires were in recent history the main disturbance agent in dry forests and grasslands, and that fire suppression has led to unnatural and "unhealthy" forest conditions. There is little doubt that low severity fires were common in many areas dominated by coniferous forests in western North America (Agee 1993), with some of the strongest evidence for frequent low severity fires from the dry Ponderosa pine forests in the southwestern United States (e.g. Covington and Sackett 1989).
However, there is mounting evidence that supports the concept of a mixed severity fire regime, especially on more mesic sites and at northern latitudes (Shinneman and Baker 1997, Veblen et al. 2000, Noss et al. 2006) with fire effects ranging from low to high severity in a complex mosaic within a single fire and across the landscape. For example, Wong (1999) found evidence to support the mixed-severity model in her study in the Stein Valley in southern British Columbia. Her work on the age structure of stands suggests only about 25% of the fires in her study area were low severity underburns. Shinneman and Baker (1997) also reported a mosaic of forest types in the Ponderosa pine forests in the Black Hills of South Dakota. Xeric sites had more open stands that would reflect periodic low severity fires, while mesic sites in valleys and northerly aspects often supported old forests in dense stands that likely arose from stand replacing fires. Similarly, studies by Taylor and Skinner (1998) in northern California report similar evidence for a mixed severity fire regime in some areas of dry conifer forests.
Dry-belt Douglas-fir forests extend over several million hectares in the Southern Interior Forest Region (SIFR) and represent a valuable resource from an economic, social and ecological perspective. The proximity of these stands to urban centers and mill sites makes them commercially valuable and both the timber and livestock industry will continue to rely on them for timber and forage. These forests surround many of the communities in the Southern Interior, underlining the importance of maintaining recreational opportunities and the need to implement effective fuels management to reduce the risk of uncontrolled wildfire in the urban-wildland interface. The ecological value of these sites is similarly high due to less severe temperatures and snowpack than at higher elevations in winter. Many species of wildlife, from native ungulates to cavity nesting birds undertake seasonal movements to lower elevations in winter, emphasizing the habitat value of these stands.
The main objective of the Isobel project is to develop and apply prescriptions to maintain prolonged open canopy conditions in dry Douglas-fir (e.g. IDFxh) forests in a cost-effective manner, while maintaining timber, forage and ecological values. Work by the Kamloops Region NDT4 Committee recommended that 10% of the dry-belt forests should be managed to create or maintain open canopy conditions. Unlike fire which is at best difficult to manage, harvesting and related silvicultural activities have a long tradition of being used to guide stand development toward desired conditions. The Isobel project applies and tests prescriptions to create and maintain open canopy conditions in dry Douglas-fir (IDFxh2) forests. The work at the Isobel site applies a rigorous sampling design to the monitoring of diverse indicators of timber, forage and ecological condition. We are simultaneously evaluating several management options, including harvesting, site preparation and livestock management for their efficacy in achieving desired open conditions, and their effects on timber and ecological indicators. The Isobel project was designed to examine five key dry-belt management issues in relation to several overstory and site preparation treatments. The monitoring will address: 1. Conifer regeneration, 2. Grass, forb and shrub species composition and abundance, 3. Understory productivity as indicated by annual growth, 4. Fuel loading and 5. Timber growth and wood quality. The design is being implemented with three overstory harvesting treatments distributed across 12 available treatment blocks. The 12 units span a range of moisture conditions, but in general, there are 6 submesic and six mesic blocks on the west and east half of the study area respectively. Average block size is 18 ha, and the overall total for the site is approximately 250 ha. In 2003, harvesting removed between 50 and 80% of the merchantable volume. There are four control (unharvested) blocks, four 50-60% volume removal blocks and four 75-80% volume removal blocks. Response to the harvesting treatments is being monitored at 170 permanent sample plots systematically distributed across the site, and 2160 1m2 vegetation plots are being used to monitor vegetation and regeneration response to the site preparation and livestock exclosure treatments . These will be analyzed as a regression design with site moisture as a co-variate since within treatment stand heterogeneity is high. A split-plot design was used to allocate site preparation treatments (control, no treatment; mechanical screefing and prescribed burn) embedded within each of the 12 harvest blocks. The split-plot treatments will be used to examine vegetation response in relation to site preparation and livestock grazing (exclosure and open to surrounding livestock grazing). Additional small experimental manipulations are being used to provide information on the rate of establishment or survival of conifer seedlings and transplanted bunch grasses (rough fescue) in relation to understory site disturbance and light conditions.


Final Report (34Kb)

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Updated August 16, 2010 

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