Microclimate within beech stands—part II: thermal conditions

Within the framework of an interdisciplinary project on the effects of climate and forest management on beech-dominated deciduous forests (Swabian Jura, south-western Germany), forest meteorological investigations are carried out to analyse the influences of exposure and canopy density on the microclimate within various beech stands (Fagus sylvatica L.). This second paper of the series Microclimate within beech stands focuses on the thermal conditions that exist mainly in the near-surface layer at different test plots. They were analysed by air temperature, T_a, (at 1.5 m a.g.l) and soil temperature, T_s, at six depths measured continuously in the period 1999–2003. The main results can be summarized as follows. (1) The thermal situation within the beech stands described by T_a depended primarily on the turbulent air-mass exchange conditions which were based on the slope-specific energy balance of the forest floor and advective heat fluxes. (2) The thermal situation within the soil described by T_s at 3 and 20 cm depth was governed by the molecular heat transport. Therefore, the heating and cooling rates of T_s were always lower than for T_a. Higher T_a and T_s values for the test plots on the SW slope showed that the thermal conditions within the beech stands depended primarily on the exposure. (3) Based on slope-specific differences of daily extremes of T_a and T_s at 3 cm depth between the silviculturally treated and control plots, the influence of the more pronounced height growth of the understorey vegetation under the near-surface thermal conditions could be clearly verified for the NE slope.Abbreviations PAR Photosynthetically active radiation - PAI Plant area index - LAI Leaf area index     

Modelling and simulation of deformation behaviour during drying using a concept of linear difference method

This study deals with the development of a two-dimensional model to simulate the deformations in wood samples during the wood drying process for the evaluation of the drying quality. The samples cut from sapwood of beech were used to analyse the moisture content distribution of the samples at two different drying conditions. A new concept based on a linear difference method was developed to use the moisture content distribution of the samples for the simulation process to predict deformation due to casehardening. The real deformations of the prongs were compared with the simulated ones for further improvements. The results show that the model can be used to simulate the deformations independently from different drying times and drying conditions. A good comparison between real and simulated changes in deformation was found for the drying process at constant climate conditions. The results provide a useful basis for further investigations on the modelling and simulation of the deformation of the samples due to different drying processes.