Thurston County, WA Landscaping Rules: Tree Removal & Heritage Trees (2026)

All sites which are subject to provisions in this chapter shall retain or replant trees to maintain an average of one hundred tree units per acre.2.Calculation. If the calculation of the number of trees results in a fraction of 0.5 or greater, the applicant shall round up to the next whole number. If the calculation of the number of trees or shrubs results in a fraction of less than 0.5, the applicant shall round down to the previous whole number.3.As trees grow, thinning is allowed to maintain appropriate density.4.Landmark Trees. At a minimum, applicants shall retain thirty percent of landmark trees on site, preferably reflective of the diversity of species and age within the stand. All retained landmark trees shall be shown to be windfirm. To determine quantities of trees using a survey, standards shall follow accepted industry methods as determined by a qualified forester.5.Heritage Trees. At a minimum, seventy percent of heritage trees on site shall be retained. All retained heritage trees shall be shown to be windfirm. Where a sampling method is proposed for treed project sites, standards shall follow accepted industry methods as determined by a qualified forester.B.Tree Units. All trees on-site that meet the standards of this section and are retained may be counted toward the minimum tree unit requirements as outlined in Table 17.27.400-1 below. Tree units are also established in this chapter for replacement seedlings. Table 17.27.400-1. Tree Conservation Categories