Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091060

    Regeneration in Thinned and Unthinned Uneven-Aged Interior Douglas-fir Stands
Project lead: Marshall, Peter (University of British Columbia)
Contributing Authors: Marshall, Peter L.; LeMay, Valerie M.; Day, Ken; Zumrawi, Abdel-Azim
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
The Interior Douglas-fir (IDF) biogeoclimatic ecosystem classification (BEC) zone of British Columbia is found on low- to mid-elevations in the south-central interior of the Province and is characterized by forests dominated by interior Douglas-fir (Pseudotsuga menziesii var. glauca (Mirb.) Franco). On the driest parts of this zone, Douglas-fir is frequently found growing in an uneven-aged, fire-dominated, sub-climax. The zone extends into Alberta, Montana, Idaho, Oregon, and Washington (Hope et al. 1991). The IDF zone covers approximately 5% (4.3 million ha) of British Columbia (Ministry of Forests 1995).

The IDF is structurally complex due to a history of disturbances from partial cutting, insects, and fire; this is particularly true in the drier parts of its range. Many pockets exist within stands where the density of saplings is quite high. Individual tree growth rates within these pockets are generally low. This contributes to low stand growth rates, low tree and stand vigour, slender form and can result in many years being required to produce large dbh trees. Losses to bark beetles, defoliators and snow press are common.

Uneven-aged interior Douglas-fir stands form an important portion of the harvest in the Southern Interior Region. This forest type also provides recreation opportunities, views from travel corridors, and ungulate winter range. Interior Douglas-fir stands are structurally complex due to a history of disturbances from partial cutting, insects, and fire. Guidance under General Wildlife Measures for mule deer in the Cariboo requires the maintenance of these complex Douglas-fir stands. Despite the local importance and complex dynamics of this forest type, relatively little research effort has been focused on improving predictions of its dynamics.

Sufficient quantities of regeneration are required to maintain the existing structure of these stands. Much of the regeneration in this type occurred historically following light surface fires; however, the historical fire regime has been drastically altered over the last century. It is uncertain whether the disturbance introduced by partial cutting and insects will promote natural regeneration in sufficient quantities to maintain stand structures through time.

Two long-term studies involving uneven-aged Douglas-fir stands were established in the Knife Creek Block of the UBC Alex Fraser Research Forest in the late 1980s. The Knife Creek Block is located in the IDF dk3 subzone (Hope et al. 1991). The landscape is gently rolling with an elevation of approximately 1000 m. Most of the plots are located on zonal (mesic) sites, with some plots on slightly drier sites. However, between-site variation is minimal and does not warrant any changes in site classification. Douglas-fir is by far the most prevalent species, accounting for approximately 90% of the trees in the plots. Other tree species present are lodgepole pine (Pinus contorta var. latifolia (Engel.)), spruce (Picea glauca (Moench), Picea engelmanni (Parry) and their crosses), white birch (Betula papyrifera (Marsh.)) and trembling aspen (Populus tremuloides (Michx.)). Establishment details are described in Marshall (1996) and Marshall and Wang (1996).

The trees on the plots in both of these studies are stem mapped and have been re-measured several times, most recently following the 2003 growing season. The first study consists of three different stand structures (6 plots). Partial harvesting took place on these plots in 2005. The second study is a replicated pre-commercial thinning experiment involving three treatments cut in 1991, and a control (24 plots). Lodgepole pine trees on these plots were killed by mountain pine beetle in 2001-2004. To date, the focus of these studies has been on the growth of the residual trees.

The aim of this project is to take advantage of the variety of stand structures and treatments included in the two studies described above to relate the quantity and quality of the natural regeneration present to the existing stand structures and their treatment history. A secondary benefit is that this study will follow and document the recovery of these stands from the loss of much of the lodgepole pine component.

Permanent regeneration plots will be established at several locations on each of the existing PSPs, where the quantity and quality of regeneration present will be assessed. The regeneration plots will be located in the PSPs in such a way as to represent average conditions (systematic plot locations), as well as situations where good regeneration is present (subjective plot locations). All trees on the PSPs will be re-measured to obtain their dimensions as of the end of the 2007 growing season. Discriminant analysis will be used to assess which neighbourhood features (local tree density, plot conditions, etc.) are useful for separating the “good” regeneration plots from the average conditions. Information gained from this analysis will be used to help determine the form of models which will be used to predict the quantity and quality of regeneration present on each regeneration plot. These models will also include as appropriate the treatment history of the stand and the species and dimensions of the trees in the vicinity of the regeneration plot. Since the trees on the existing plots are stem mapped, it will be possible to assess the impact of a variety of sizes of neighbourhoods surrounding each of the regeneration plots. The results of this study should allow better assessment of the potential impact of different partial cutting intensities on the subsequent quantity and quality of natural regeneration.

Hope, G.D., W.R. Mitchell, D.A. Lloyd, W.R. Erickson, W.L. Harper, and B.M. Wikeem. 1991. Interior Douglas-fir zone. In: Ecosystems of British Columbia. D. Meidinger and J. Pojar (eds.) BC Ministry of Forests, Research Branch. pp. 153-165.
Marshall, P.L. 1996. Response of uneven-aged Douglas-fir to alternative spacing regimes: analysis of the initial impact of the spacing regimes. Canada - British Columbia Joint Publication FRDA-II Report 242. 27 pp.
Marshall, P.L. and Y. Wang. 1996. Growth of uneven-aged Douglas-fir stands as influenced by different stand structures. Canada - British Columbia Joint Publication FRDA-II Report 267. 20 pp.
Ministry of Forests. 1995. Forest, range, and recreation resource analysis, 1994. Province of British Columbia, Victoria, BC.


Meaurement summary (0.3Mb)
Extension report (0.6Mb)
Final report (0.6Mb)

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Updated August 16, 2010 

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