The contribution of red wood ants to soil C and N pools and CO2 emissions in subalpine forests

Little information is available regarding red wood ant (RWA; Formica rufa group) impacts on soil carbon (C) and nitrogen (N) cycling in forest ecosystems. We found that RWA mound density (number per ha) was linked to forest tree species composition, slope aspect, and canopy closure. The size of RWA mounds was positively correlated with successional age of the stands. C and N concentrations of mound material were significantly higher than in the forest floor, while C:N ratios were not. RWA mound C and N pools were found to be significantly lower (<= 990 kg C/ha and <= 21 kg N/ha) than in the forest floor. RWA mounds were "hot spots" for CO2 emissions ranging from 12.4 (mid July) to 3.5 (early September) times higher than the adjacent forest floor. Overall, they contributed 0.7-2.5% to total forest soil CO2 emissions. Consequently, the contribution of RWA to total forest soil C and N pools and forest CO2 emission is minor and likely not important when calculating or modeling C and N pools or C fluxes. Yet, RWAs increase the spatial heterogeneity of soil C and nutrients and alter the flow of energy within their habitat.