The Effect of Mulch, Drip Irrigation, and Irrigation Supplement On Native Conifer Establishment In Seattle Parks

This study investigated the efficacy of common tree seedling establishment methods at two Seattle parks in the context of Seattle urban forest restoration.  Drip irrigation, irrigation supplement (DriWater gel packs), and woodchip mulch were tested alone and in combination.  Three native conifers were tested in the study: Thuja plicata, Abies grandis, Tsuga heterophylla. Stem water potential, soil moisture status, and site analysis suggest that 1) seedling mortality was highly site specific, 2) summer drought was responsible for seedling mortality in Seattle parks, and 3) woodchip mulch could be an economic way to alleviate water stress. Our findings also emphasize the need for site and species-specific methods for conifer establishment in Seattle parks.