Abstract
For economic and biodiversity reasons, it is important to retain a range of tree species across timber supply areas. A trial testing a uniform shelterwood silvicultural system was initiated in the Sub-Boreal Spruce biogeoclimatic zone in the Central Cariboo Forest District (Williams Lake) in 1990 to develop harvesting strategies that would promote regeneration of Douglas-fir (Pseudotsuga menziesii) on sites where Douglas-fir had been the leading species in the mature stand. The traditional method of clearcutting, followed by planting, was not successful because of poor seedling performance due to the susceptibility of Douglas-fir seedlings to frost damage. Currently there are no stocking or free-growing standards for shelterwoods in this zone. Information is needed to support decision-making for shelterwood silvicultural systems, including species selection and harvesting methods.
The initial harvesting entry in 1991 focussed on removing 30% (preparatory cut) or 50% (regeneration cut) of the initial basal area. Early results from the first harvest entry in 1991 up to 1998 are reported by Burton et al. (2000) and Waterhouse (1999). In early 2001, a second harvesting entry was made into two of the original treatment units (30 m2 and 40 m2), further reducing the extant basal area by 50%. This produced a range of residual basal area (RBA) treatments: (1) 15 m2 (second regeneration cut), (2) 20 m2 (preparatory cut plus regeneration cut), (3) 30 m2 (regeneration cut), (4) 40 m2 (preparatory cut), and (5) 60 m2 (no harvest), replicated on three sites. This extension note describes trial results for the 5-year period after the second harvest for seed-fall, vegetation, natural regeneration, planted stock, tree fall, and microclimate.
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Updated April 12, 2007
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