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State guidance on 'site potential tree height' figures in Whitman County stream buffer discussion
Summary
Consultant Dan Nickel explained Department of Fish and Wildlife guidance that recommends using 'site potential tree height' to set riparian buffers where soils/mapping exist and a 100-foot minimum elsewhere; commissioners asked how that approach applies in largely non-forested Whitman County.
At the March 4 workshop, consultant Dan Nickel briefed commissioners on Department of Fish and Wildlife guidance proposing 'site potential tree height' as a basis for riparian buffers instead of traditional stream typing. He said mapped soils in Whitman County contain limited areas with a tree-height index, meaning much of the county would fall back to a 100-foot minimum buffer where the mapping is absent.
Nickel noted DFW used a 200-year site-potential tree-height index for tall-canopy systems in some parts of the state, but Whitman County’s mapped polygons show predominant values far lower (predominant width cited as about 143 feet where a value exists). He proposed the county could simplify stream typing and still remain consistent with best-available science. Commissioner Dave Gibney questioned how tree-height-based buffers apply in shrub-steppe or agricultural areas and asked whether that approach creates new restrictions; Nickel replied that where tree-height data are absent the state's recommended 100-foot minimum would apply and that much of Whitman County lacks mapped canopy soils.
