Although S. paschale fixes N at a high rate per unit biomass ( Crittenden and Kershaw, 1978), the relatively small biomass of this species limits the total N contribution to the ecosystem ( Gavazov et al., 2010). Juniper was found to be present in relatively high density in the reference forest, R428 manufacturer but is basically absent on the degraded forest stand. Juniper is highly sensitive to frequent fire and was likely lost to a combination of fire and removal for fuel wood (
Diotte and Bergeron, 1989, Thomas et al., 2007 and Ward, 1973). There is little C or N accumulation in the O horizon of the spruce-Cladina forests. The low level of C accumulated in the O horizon is reflected in C:N ratios which were nearly twice as high on reference forest sites
as compared to spruce-Cladina forests ( Table 2). The O horizon is the primary site of nutrient uptake in boreal forest soils ( Fisher and Binkley, 2000 and Kimmins, 2003). The loss of N capital from these soils directly reflects a reduction in productivity potential and a reduced potential for regeneration. The lack of difference in mineral soil C and N between the two forest types was relatively surprising given the long-term differences in O horizon C and N values. Total N in surface mineral soils to a depth of 10 cm is nearly equivalent to the total N in the O horizon of the reference forest, but is now the primary source of N in the spruce-Cladina forests. PD98059 supplier This is important, because it implies the requirement for a shift in nutrient acquisition strategy from accessing N from the O horizon BCKDHB to accessing N via the mineral soil. Interestingly, roots of both spruce and birch in the Cladina dominated forests are exposed on the
surface of the O horizon perhaps allowing for access to nutrients in both the shallow O horizon and surface mineral soil. Charcoal contents of the mineral soil (0–5 cm) of lichen dominated forests were surprisingly lower than that in the reference forest. Charcoal as a percent of total C was 15.6 (±4.8 se, n = 9) for the reference forest and 5.2 (±0.5 se, n = 9) for the spruce-Cladina forest. This is possibly due to the consumption of charcoal during recurrent fire events when there is little surface fuel in frequently burned sites ( DeLuca and Aplet, 2008 and Pingree et al., 2012). Total P reserves in the surface mineral soils appeared to have been greatly reduced by repeated burning. This could be a result of volatilization of P, but the lack of fuel loading in the spruce-Cladina forest would suggest that there was little capacity to lose P by this mechanism as volatilization temperatures of 650 °C ( Neary et al., 1999) were not likely reached once initial fuel beds were consumed in earlier fires. It is more likely that the loss of vegetation from these sites resulted in a lack of plant recycling of P into surface soils and perhaps resulting in a net leaching of P below the rooting zone in presence of limited of vegetative uptake.