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Engelmann spruce and subalpine fir seed dispersal in the ESSF wet cold subzone Kraft, Daniel Nathan

Abstract

Conventional silviculture practices used on lower elevation stands have failed to adequately restock stands within the Engelmann spruce/subalpine fir zone (Butt 1990, Farnden 1994). The supply of viable seed is critical for successful natural regeneration (Rowe ei a[. 1970). This study was conducted at the Sicamous Creek site in the ESSF zone of interior British Columbia over the winter of 1997-1998. Four harvest treatments (Individual Tree Selection (ITS), 0.1 ha cut, 1 ha and 10 ha clearcuts) were analyzed in terms of the seed dispersed by the Engelmann spruce (picea engelmanni) a n d subalpine fir (Abies lasiocarpa) trees remaining after harvest. The spruce seed populations in the ITS and 0.1 ha treatments were not statistically different from the uncut spruce seed population; however, the quantity of fir seed was reduced significantly. Within the 10 ha and 1 ha clearcuts the relative composition of Engelmann spruce to subalpine fir seed increased to a ratio of over 5 to 1 from 1.7 to 1 in the uncut stands. This compositional change suggests spruce seed is more amenable to wind dispersal than fir seed. The south edge supplied the most seed into the clearings, while the north edge contributed the least. The amount of seed deposited closest to an edge was positively correlated to the frequency of its respective prevailing winds; however, the magnitude of the relationship declined as the clearing decreased in area. A mechanistic seed dispersal model (DISPERSE) was developed to estimate the spatial distribution of seed in a clearing. The spatial distribution of spruce and fir seed were simulated for the wind directions and velocities recorded at the Sicamous Creek site, in conjunction with the corresponding tree heights and aerodynamics inherent to the seeds. DISPERSE estimated the spatial distribution of seed in the 10 ha clearing accurately; however, its predictions did not adequately characterize the decline of seed densities with distance from the edge in the 1 ha clearing.

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