The Date Creek silvicultural system

The Date Creek silvicultural systems study (Coates et al., 1997) was established in 1992, in northwestern British Columbia, Canada, approximately 21 km north of Hazelton, west of the Kispiox River (55”22’N, 127”5O’W; 370-665 m elevation). Date Creek is within the moist cold subzone of the Interior Cedar-Hemlock biogeoclimatic zone (ICHmc; Banner et al., 1993), a transitional area between the interior and coastal forests of northwestern British Columbia (Pojar et al., 1987; Meidinger and Pojar, 199 1). Mature forests (140 yr> in the area are mixtures of conifer and deciduous tree species. Western hemlock (Tsuga heterophylla (Raf.) Sarg.) dominates; other species include western redcedar Thujaplicata (Dougl. ex D. Don), subalpine fir (Abieslasiocarpa (Hook.) Nutt.), lodgepole pine (Pinuscontorta var. latifolia Engelm.), hybrid spruce [the complex of white spruce (Picea gZauca (Moench) Voss), Sitka spruce (P. sitchensis (Bong.) Carr.) and occasionally Engelmann spruce (P. engelmannii
Parry ex Engelm.)], paper birch (Betula papyrifera Marsh.), trembling aspen (Populus tremuloides Michx.), and black cottonwood (Populus balsamifera spp. trichocarpa Torr. & Gray). Old-growth forests (250-300 + yr) are dominated by western hemlock with varying amounts of western redcedar and some amabilis fir ( Abies amabilis Dougl. ex
Forbes). Amabilis fir abundance increases with elevation.
Four tree removal treatments (in approximately 20 ha treatment units) were replicated four times (16 units in total), in a randomized block design, with combinations of ecological site type and forest age as the blocking factor (mesic 140 yr; mesic-submesic 140 yr; mesic-subhygric 140 yr; mesic 350 yrl. The treatments involved increasing levels of tree removal: (1) no tree removal; (2) light tree removal
where approximately 30% of the stand volume was removed as single stems and small groups (similar to a single-tree or group-selection, or a light initial
shelterwood removal; Table 1); (3) heavy tree removal where approximately 60% of the stand volume was removed using a combination of small patch cuts (1000-5000 m*> and single-tree to small group-selection within the forest matrix between the
patch cuts (similar overall to an irregular shelter- wood system: Table 1): and (4) total removal of all merchantable trees or clearcut. Across the three treatments where trees were retained, a gradient of gap sizes was created from very small (removal of a single tree) to 5000 m’. We determined gap size, gap density and total gap area within all treatment units except the clearcut. Transect lines were established 50 m apart tapproximately 3600 m of line) on maps of each treatment unit. From these lines. approximately 2000 m of transect line was randomly selected. The total length of fine in canopy gap and forest matrix was recorded. The size of each canopy gap encountered was determined using methods described by Runkle (1992).