AbstractsBiology & Animal Science

Forest ecosystems play a key role in the Earth's carbon cycle, as their uptake of carbon dioxide is largest in the terrestrial biospheres (CO2 sink). Despite a vast number of ecological studies about forest ecosystem, there are still outstanding issues about prevailing meteorological conditions, turbulent and coherent structures and exchange processes of heterogeneous forest ecosystems. Therefore, this thesis is related to the joint research project EGER IOP3 (ExchanGE processes in mountainous Regions – Intensive Observation Period 3), aimed at the investigation of diurnal cycles of energy, matter and (non-)reactive trace compounds in the soil-vegetation-boundary-layer-system at a forest edge within a heterogeneous forest ecosystem in a very complex terrain in mid Europe. Well established measurement techniques were used, such as the eddy-covariance method for determination of turbulent/coherent fluxes and for detection of different vertical and horizontal coupling regimes. SODAR/RASS systems were used to investigate boundary layer phenomena. Additionally, a novel, fully automatic Horizontal Mobile Measuring System (HMMS) was successfully developed, applied and assessed within this thesis. The HMMS was installed on a 150 m long transect perpendicular to the forest edge, to obtain higher information density about horizontal gradients of eight quantities (short/long-wave down/upwelling radiation, temperature, humidity, CO2 and O3 concentration). The experimental design, with 3D installation of the towers/masts, HMMS and profiling systems was ideal for the investigation of the research issues mentioned above. By combination of all measurement techniques, significant differences could be observed along the transect forest – forest edge – clearing (three locations), with strong distinctions in the vicinity of the forest edge. The highest gradients in the HMMS measurements occurred near the forest edge. Furthermore, it could be observed that the turbulence influenced quantities in the HMMS measurements (temperature, humidity and trace gases) were mainly affected by the prevailing vertical structures at the forest edge, while the influence decreased the further away from the forest edge. These findings coincide with the findings for coherent structures, where only at the forest edge a significant daily variation could be observed for ejections and sweeps, with strong ejection motions during daytime (updraft) and strong sweep motions during nighttime (downdraft). The thermal updraft during daytime could be attributed to the highest temperatures occurring near the forest edge (1.5 K warmer than at the clearing and within the forest) and the advective transport of energy towards the forest edge. The reverse was also apparent, where energy was transported off the forest edge towards the clearing. Nevertheless, highest energy and CO2 fluxes, as well as highest variation could be observed at the forest edge. This leads to a better energy balance closure at the forest edge (Residual Res = 17 %), compared to both other…