The extremely limited accumulation of NH4+ on ionic resins in the spruce-Cladina forest could be a function of the high rate of NO3− formation in these same soils which could lead to N losses due to leaching and or denitrification ultimately reducing the amount of mineralizable N. The combined effect of the loss of N2 fixing feathermosses and loss of juniper from the understory likely led to a reduction in success of germination and growth of pine or birch seedlings. Juniper has previously been reported to increase the surface concentrations of available P and create a microhabitat for feathermoss growth (DeLuca

and Zackrisson, 2007). It is suspected that the juniper also Pembrolizumab cost serves as a nurse crop for the growth of pine and spruce seedlings

as it serves to protect young saplings from trampling and browse by reindeer (Castro et al., 2004). In comparing pine seedling survival and growth in open bare ground compared to under spiny shrubs and under juniper, Castro et al. (2004) found the highest rate of survival under juniper shrubs. Juniper is highly flammable and readily eliminated from sites exposed to IPI-145 mw frequent, recurrent fire (Thomas et al., 2007). Accordingly, the loss of juniper from the spruce, pine forests of northern Sweden as a result of recurrent burning, would have likely led to a decline in the presence of fertile microsites associated with juniper (DeLuca and Zackrisson, 2007) and loss of the protective cover created by juniper shrubs. Loss of these two components of the plant community would build upon itself ultimately resulting in a reduction in the presence of pine and birch in the soil seed bank. The development of an open spruce canopy with a forest floor dominated by lichen and partial dwarf shrub cover would provide limited protection against erosion and result in limited accumulation of organic matter. Cladina spp. harbor green algae as a photobiont rather than cyanobacteria and therefore do not

exhibit the capacity for N2 fixation observed in cyanolichens ( Yahr et al., 2006). And in spite of the fact that Cladina may harbor bacteria with nif genes ( Grube et al., 2009), attempts to SSR128129E measure nitrogenase activity in Cladina have been negative (Zackrisson, unpublished data). Stereocaulon, a lichen capable of relatively high rates of N fixation per unit biomass ( Crittenden and Kershaw, 1978), accounts for 10–20% of the ground cover in the Cladina-lichen forests, the total N contribution is likely to be extremely small given the limited biomass per unit area ( Gavazov et al., 2010). In the undisturbed Scots pine, Norway spruce reference forest, the feathermoss P. schreberi alone accounts for over 70% ground cover. Nitrogen fixation in P.