EFFECTS OF FERTILIZER ON BRYOPHYTES IN SWEDISH EXPERIMENTS ON FOREST FERTILIZATION

Swedish experiments on the optimal fertilization for forests were used to study the effects of ammoniUM nitrate, urea, and a compound PK fertilizer on bryophytes. The experiments were analysed with ANOVA. The abundance of Brachythecium oedipodium, B. reflexum, and B. starkei was significantly raised by addition of ammonium nitrate or urea. However, at doses larger than 60 kg N/ha/year these species tended to decline. Hylocomium splendens and Pleurozium schreberi declined strongly at nitrogen doses of 30-60 kg N/ha/year. We could not confirm that bryophytes and lichens are more sensitive to urea than to ammonium nitrate. Addition of PK, whether alone or combined with ammonium nitrate or urea, has minor but significant effects upon bryophytes, additional to those of nitrogen. The results support the hypothesis that some recent changes in the composition of the herb and bryophyte layer of W European forests are caused by raised levels of soil N.