Response of Gaultheria shallon and Epilobium angustifolium to large additions of nitrogen and phosphorus fertilizer

A study was established in coastal British Columbia to determine if repeated nitrogen (N) and phosphorus (P) fertilization negatively influences the reestablishment of salal (Gaultheria shallon Pursh) on cleared and burned cedar–hemlock (Thuja plicata Donn ex D. Don – Tsuga heterophylla (Raf.) Sarg.) forests. Fertilizers were applied for 3 years, and the biomass of ground vegetation and conifer seedling survival and growth were measured. Salal biomass decreased with high levels of N application (1000 kg N/ha), but not when 400 kg P/ha was added with 1000 kg N/ha. The addition of 500 kg N/ha, with or without P, stimulated salal growth. The biomass of fireweed (Epilobium angusti folium L.) increased with the addition of N + P but not with N alone. In the high N and N + P treatments, conifer seedling survival and heights were reduced. These results confirm earlier reports that salal responds negatively to high N applications and that this negative response can be alleviated with simultaneous additions of P. The response of fireweed to N + P, but not to N alone, suggests that the abundance of this species is more indicative of P than N availability.