Short‐term growth response of jack pine and spruce spp. to wood ash amendment across Canada

Wood ash amendment to forest soils contributes to the sustainability of the growing bioenergy industry, not only through decreased wood ash waste disposal in landfills but also by increasing soil/site productivity and tree growth. However, tree growth studies to date have reported variable responses to wood ash, highlighting the need to identify proper application rates under various soil/site conditions to maximize their benefits. We explored the influence of tree species, wood ash nutrient application rates, time since application, stand development stage, and initial (i.e., before wood ash application) soil pH and N on short‐term tree growth response to wood ash amendment across eight unique study sites spanning five Canadian Provinces. Jack pine (Pinus banksiana Lamb) had the most positive response to wood ash amendment compared to white (Picea glauca Moench), hybrid (Picea engelmannii x glauca Parry), and black spruce (Picea mariana Miller), where increasing nutrient application rates increased height growth response. In comparison, black spruce had the most negative response to wood ash amendment, where increasing nutrient application rates slightly decreased height growth response. Site as a random effect explained additional variation, highlighting the importance of other unidentified site characteristics. By examining trends in short‐term growth response across multiple studies with variable site characteristics, we found growth response differed by tree species and nutrient application rates, and that jack pine is a promising candidate for wood ash amendment. These results contribute to our knowledge of optimal wood ash amendment practices and environmentally sustainable bioenergy production. Applying wood ash to forest soil closes the bioenergy production loop by diverting a waste product from landfills back to the forest as a soil amendment. There is a need to identify proper application rates under various soil/site conditions. By examining short‐term trends in tree growth response to ash across eight sites spanning five Canadian provinces, we found that jack pine responded positively to increasing quantity of ash nutrients, and showed the greatest potential for increased productivity when compared to spruce species. These results provide a baseline for monitoring programs, and contribute to our knowledge of optimal ash amendment practices.