Survival, height and health status of 20‐year‐oldpinus sylvestrisandpinus contortaafter different scarification treatments in a harsh boreal climate

Survival, height, and health status of Pinus sylvestris and Pinus contorta were studied in a randomized factorial experiment in northern Sweden. Treatments studied per species were no scarification (control), patch scarification, and mounding. The experiment was evaluated 18 years after planting. For both species, survival was higher in mounded plots than in control plots. Pinus contorta was 11% higher than P. sylvestris in the treatment with highest survival, but this difference was not significant. Ninety‐three per cent of the P. contorta trees were infected and 22% killed by Gremmeniella abietina compared with 21% and 5% for P. sylvestris. Eighty‐three per cent of the P. sylvestris trees were infected and 24% killed by Phacidium infestans compared with 8% and 2% for P. contorta. Leaning P. contorta trees were more severely damaged by G. abietina than those not leaning. Mounding reduced the mortality caused by G. abietina in P. contorta and by Ph. infestans in P. sylvestris. Due to the increasing mortality of P. contorta during the past 6 yrs, and the high frequency of G. abietina, the number of surviving trees of the two species are approaching equality. Significantly more P. contorta than P. sylvestris trees were leaning and had poor stem quality. Regardless of species, mounded plots showed the highest frequency of broken tops. Results suggest that more than 20 yrs need to elapse before regeneration efforts with these two species in harsh areas can be evaluated reliably.