The third EGER experiment will be conducted at the FLUXNET site Weidenbrunnen Waldstein (DE-Bay), located in North-Eastern Bavaria in the Fichtelgebirge Mountains. Because of the wind throw by “Kyrill” the large disturbed and deforested area appeared in the vicinity of the measuring site. It is well known that forest heterogeneities increase the loss of green house gases of an ecosystem with significant feedbacks on the climate system. Therefore, particular emphasis of the investigations will be placed on the detailed analysis of these heterogeneities and clear cuts due to wind and pests on transfer and chemical processes.
The heterogeneities on a scale of several hundreds of meters generate secondary circulations which intensify the energy and gas exchange. These phenomena cannot be measured adequately e.g. because of the effect of the so-called unclosed energy balance. In the frame of the experiment we will use Large-Eddy Simulations in combination with a forcing by measured surface fluxes to investigate such phenomena.
The modeling, remote sensing and flux measuring techniques will be used to analyze the events of free convection with strong updrafts of trace gases due to open and heated clear cuts. Up to now such experiments are lacking and these events are not included in any modeling studies. The forest edge will be investigated as a source of coherent structures which influence the exchange processes in the whole area and may be the reason for possible horizontal decoupling between forest and clear cut at day time on the lowest meters. Effects of night time low level jets on the night time exchange process will be analyzed.
Expected development of secondary vegetation which is different in their phenology, and leaf physiology from the original Picea abies together with the differences in turbulence between clear cut and forest gives a possibility to investigate a heterogeneous sink/source distribution for reactive and non reactive trace gases.
The partitioning between sensible and latent heat flux on the clear cut is expected to increase, increasing the sensitivity of the clear cut area to spatial and temporal water availability. This might affect biogeochemical processes in the soil and nutrients flows. An earlier depletion of soil water reservoir might shift the ecosystem into a state of lower resilience with respect to water exploitation, making it more susceptible for exogenous events as unusual rainfall pattern.
Niederschlag: 4.28 mm/24h
Sonnenschein: 4 h/d