Controls of soil respiration in a mixed forest

Soil respiration (R_soil) reflects the second largest CO₂ flux in ecosystems and is the main contributor to ecosystem respiration. Yet, heterogeneous patterns on spatial scale are difficult to identify due to complex dependencies of R_soil on various spatial variables. Within the framework of the SFB1537 ECOSENSE our aim is to quantify hot spots and hot moments for R_soil in a mixed forest.

The ECOSENSE Forest site is located in the foothills of the southwestern Black Forest (Germany) and consists dominantly of Fagus sylvatica and Pseudotsuga menziesii growing on acidic soils. Spatio-temporal patterns were assessed by weekly to bi - weekly repeated measurements on 35 plots over two years. The patterns were then analysed using a multiple-mixed regression model that considers weather, phenology, tree distribution and soil physical, chemical and biological properties.

The temporal pattern of R_soil reflected a pronounced seasonality, but a high proportion in variability could be explained by meteorological data or soil temperature. Within the area, various hot and cold spots were present, which changed throughout the seasons. The spatial pattern depended on combined effects of tree species and associated root density, soil type and nutrient availability.

Our present dataset achieves a high spatial resolution not often found in other studies. Our analysis showed influences of weather phenomena, which are of crucial importance in the scope of climate change and therefore provide us a better understanding of the development of hotspots in forest soils in a spatial and a temporal context.