Legacy effects of non-native Cytisus scoparius in glacial outwash soils: Potential impacts to forest soil productivity in western Washington

Scotch broom (Cytisus scoparius (L.) Link) is a highly competitive, nonnative, leguminous shrub species of major concern in coast Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco var. menziesii) forests the Pacific Northwest that has potential to impact long-term soil productivity. We conducted bioassay assess for legacy effects on soils (e.g., nutrient effects, seedbank, etc.) following removal and recovery over time. The was using glacial-outwash from an existing Long-Term Soil Productivity study near Matlock, WA, USA, where had been removed or kept out 0 (broom present), 4, 10, 14 years. Soils each duration were combined with fertilizer treatments mechanisms response three native plant species: yarrow (Achillea millefolium L.), Roemer’s fescue (Festuca idahoensis Elmer ssp. Roemeri), Douglas-fir. There evidence negative growth biomass, which decreased time since removal. Responses indicated effect not associated reduced availability. In contrast, both significantly greater biomass recently present, this positive availability, likely increased N. 4 years estimated as having produce 578,500 germinants ha−1. Our results demonstrate depending responding species. Combined legacies large viable seed bank create growing conditions hinder productivity