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Establishing white spruce under aspen, 20 to 40 years before the harvest of the aspen is potentially the most cost effective scenario for boreal mixedwood management (DeLong 1997, Comeau et al. 2005). This relay of growth periods and harvest of the two species creates the most productive type of spruce aspen mixture (Man and Lieffers 1999) and closely mimics natural stand succession in western boreal forest (Lieffers et al. 1996). A major advantage to planting under a maturing aspen canopy is the ability to establish spruce in an environment that has better growing conditions than in clearcuts, particularly in terms of light levels. Light levels under fully stocked boreal mixedwood stands appear to reach minimum levels between 10 and 25 years following disturbance, and increase after that time due to development of canopy gaps (Lieffers et al. 2002). In stands over 40 years old, light levels above 20% are commonly observed (Groot et al. 1997; Lieffers et al. 2002). In addition, overstory aspen cover reduces the vigor of shrubs, herbs and grasses, which can seriously impact on the growth of small white spruce (Lieffers and Stadt 1994; Comeau et al. 2004a). Retention of overstory cover can also reduce the risk of growing season frost and overwinter injury (Groot and Carlson 1996), and damage due to white pine weevil (Pissodes strobi Peck) (Taylor et al. 1996). Underplanting can shorten the rotation length for white spruce by 7 to 10 years, it can help to achieve maintenance of forest cover, it may be better suited to creation of mixedwood stands and it may be less expensive than the system involving clearcutting, planting, and competition control to establish white spruce (Greene et al. 2002). Damage resulting from hare browsing of planted spruce can be a serious limitation to the use of underplanting. Hare damage problems can be reduced by: a) not planting during times when hare population is increasing; b) not planting in close proximity to dense young stands of aspen or dense black spruce; c) underplanting in the interior of large mature aspen stands; and, d) reducing palatability of planting stock by reducing their tissue nutrient concentrations (Radvanyi 1987; DeLong 2000; Greene et al. 2002). While hare damage was observed at the Sierra Road site, it was high only in portions of the study site which were adjacent to protective cover, and since most browsed seedlings recover, it had only short term effect on growth (Comeau et al. 2004a). Key obstacles to the operational application of this silviculture strategy are uncertainty regarding appropriate establishment conditions and stand development over time. While models for aspen ? spruce mixtures exist, the empirical data available for model predictions is extremely limited for spruce growth under aspen.
This experiment examines two sites where initial conditions, growth, and light environments have been measured from establishment of the spruce component. This project proposal is timed to assess the successional stage where white spruce would have grown above the understory shrub layer. The change in growth rate as spruce saplings move from the understory shrub layer into the light environment provided by the aspen canopy is a critical piece of information for models of spruce aspen dynamics.
Kabzems, Richard. 2008. Ten year growth of white spruce underplanted beneath spaced and unspaced aspen stands in northeastern British Columbia. Forest Investment Account (FIA) - Forest Science Program. Forest Investment Account Report. FIA2008MR029
Topic: FLNRORD Research Program
Keywords: Forest, Investment, Account, (FIA), British, Columbia
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