Early establishment of Douglas-fir and ponderosa pine in grassland seedbeds

Grasslands of interior British Columbia are being encroached upon by Dougla s-fir (Pseudotsuga menziesii var. glauca (Beissn.) France) and ponderosa pi ne (Pinus ponderosa Dougl.). A pot experiment placed in the field was condu cted to determine the effect of forest and grassland seedbeds on seedling e mergence and early establishment of the 2 species with 2 seed collections e ach. For these seedbeds, structural characteristics were evaluated and the effect of seedbeds water extracts on seed germination was determined. Seedl ing emergence of both species was significantly reduced by Douglas-fir need les and enhanced by fescue litter and cattle manure compared to mineral soi l, The rate of emergence was reduced by Douglas-fir needles and sagebrush l itter, and for some collections, by ponderosa pine needles, but was always enhanced by manure compared to mineral soil. Seedling survival was generall y not affected by seedbeds. Douglas-fir seedlings emerging earlier in the s eason survived better, and both Douglas-fir and ponderosa pine seedlings em erging earlier lived longer than these emerging later. Seed germination of ponderosa pine was not affected by the water extract while that of Douglas- fir was reduced by the water extract from sagebrush litter. Therefore, diff erences in seedling emergence of the 2 species among seedbeds were related more to structural than to chemical characteristics of seedbeds. Successful establishment of the 2 species in grasslands within this region likely rel ies on the ability of seeds to germinate early in the growing season on see dbeds in which soil moisture is conserved, as summer droughts are severe.