Response of advance regeneration to intensity of harvest and fertilization on boreal wetlands

Post-harvest nutrient status and growth of understory black spruce (Picea mariana [Mill.] B.S.P.) advance regeneration during the first seven years after harvest with advance regeneration protection (HARP) was evaluated on two boreal wetlands in northeastern Ontario. Three intensities of HARP were investigated: light, medium and heavy, corresponding to 35, 50, 100% basal area removal of merchantable trees. Limiting nutrients were diagnosed with a nitrogen (N), phosphorus (P) potassium (K) fertilization trial. Release by HARP significantly improved foliar N by 43–214%,and P by 40–317%, stimulated needle mass by 13–114% and annual height increment of spruce by 6–50% on all three HARP treatments. Growth of spruce was statistically greater after heavy release than the other two HARP treatments by the sixth year. Fertilization with a combination of N and P further increased needle biomass and height increment by 23–46% and 16–26%, respectively. Nitrogen and, secondly, P were limiting for rapid natural reestablishment of black spruce stands on boreal peatlands. Key words: black spruce, nitrogen, phosphorus, potassium, clearcut