The impact of soil temperature increase on organic matter and faunal properties in a frozen calcareous scree in the French Alps

We examine the effect of natural differences in soil temperature at two locations distant by approximately 500 m in the frozen scree of La Plagne en Chartreuse (Savoy, France). We determined humus properties, soil organisms and biologically mediated soil-forming processes in screes from a low part dominated by an open pine forest (OF, 1100 m asl) and in a top part covered by a dense pine forest (DF, 1200 m asl). Our results show a soil temperature increase of about 3.8 °C in the DF plot during June to October, but similar humus morphology at both plots. Soil pH was lower, and C/N ratio higher in the DF plot. Soil faunal composition differed between DF and OF plots for some taxa. While the abundance of the Oribatid mites was higher, abundance of Collembola was significantly lower in the DF plot. As earthworm activity was scarce at the site, Oribatid mites and Collembola presumably play an important role in the humus microstructure which was confirmed by the analysis of the humus micro-aggregation. To date, changes in the pedofaunal communities did not alter the humus form which may be explained by the complexity of biotic soil interactions and the high functional redundancy of the soil fauna.