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that plantation H/D values can be lowered and stability promoted through reduced planting
densities or early thinning; however, later thinnings may not be effective in promoting stability,
since they do not appear to lower H/D values. Higher initial planting densities shorten the time
period during which thinning can be expected to effectively lower future H/D values. Timesensitive
thinning requirements in dense plantations make their management inflexible. The
flexibility with which a stand can be managed describes the rigidity of intervention requirements
and/or potential range of stand development pathways.
666. Wimberly, M.C. and B.B. Bare. 1996. Distance-dependent and distance-independent models of
Douglas-fir and western hemlock basal area growth following silvicultural treatment. Forest-
Ecology-and-Management 89(1/3): 1-11.
Keywords: fertilization
thinning
growth
Abstract: Distance-independent and distance-dependent individual-tree basal area growth
equations for Douglas fir (Pseudotsuga menziesii) and western hemlock (Tsuga heterophylla)
growth following thinning and fertilizer treatments were developed using regression analysis.
Data came from an even-aged, naturally regenerated, mixed species stand near Jordan River, SW
Vancouver Island, Canada. Distance-independent models included only non-spatial competition
and thinning indices, while distance-dependent models included both spatial and non-spatial
indices. The distance-independent models with the highest adjusted multiple coefficient of
determination (adjusted Rsuperscript 2) for both species included diameter at breast height, crown
class, percent basal area removed in thinning, plot basal area greater than the subject tree and
stand age as independent variables. The distance-dependent models with the highest adjusted
Rsuperscript 2 included all of these variables in addition to a variant of the area potentially
available index, which is based on the spatial tessellation of the point pattern of trees in the stand.
Addition of this spatial index produced only a small (