Growth Response of Mature Trees versus Seedlings to Gaps Associated with Group Selection Management in the Sierra Nevada, California

Radial growth response of mature conifer trees to creation of gaps using group selection was measured along transects extending from gap edges into a surrounding forest in central Sierra Nevada, California. A reference sample of trees between gaps was measured for comparison. Edge depth was quantified as the distance from gaps to where radial growth of trees near gaps converged with growth of trees from the reference sample. Trees within 10 meters of gaps grew more than trees from the reference sample, with no detectable differences in this depth caused by gap size (0.1 to 1.0 ha), species (Douglas-fir, incense-cedar, ponderosa pine, and white fir), or orientation (cardinal direction) relative to the gap. The lack of orientation influence suggests increased underground resource availability and possibly an allometric adjustment to preferential radial growth as the causes of the positive edge effect. When considering these results with those reported previously from the same study, details of the stand level tradeoff between growth of planted regeneration within gaps and growth of larger trees surrounding them reveal implications of gap size choice in gap-based silvicultural regimes. Whereas early height suppression of seedlings was avoided with gap sizes above approximately 0.3 to 0.5 ha, radial growth in the unharvested forest was substantially increased with gap sizes below that same size range.