State guidance on 'site potential tree height' figures in Whitman County stream buffer discussion

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.