Seedfall and Seed Viability Within Artificial Canopy Gaps in a Western Washington Douglas-Fir Forest

Seedfall of coast Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii) has been studied at the forest edgeclearcut interface and in small canopy gaps, but it has not been evaluated in gap sizes that would be typical of a groupselection method of regeneration. In a mature Douglas-fir forest in the Puget Sound lowlands of western Washington, seedfall was measured by month in artificially created circular gaps 0.1, 0.2, 0.3, and 0.4 ha (0.25, 0.5, 0.75, and 1.0 ac, respectively) in size and in the forest matrix. Seedfall was assessed 1 year before and 2 years after gap creation, and a germination trial was used to detect potential gap and seasonal effects on seed viability. Seedfall density was not significantly affected by the presence of gaps up to 0.4 ha (1.0 ac). Germination percentage and germination rate did not differ between seed collected in gaps and that collected in the forest matrix. Seed weight and germination percentage both were highest for fall collections and declined for collections taken throughout winter and spring. We found no evidence that seed dispersal or viability would be a limiting factor in natural regeneration of Douglas-fir under a group-selection system that created gaps up to 0.4 ha (1.0 ac) in size.

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Author(s): Warren D. Devine, Timothy B. Harrington

Publication: Tree Planters' Notes - Volume 59, Number 1 (2016)

Volume: 59

Number: 1