Thomas Holst

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, Ta, (at 1.5 m a.g.l) and soil
temperature, Ts, 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 Ta 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 Ts at 3 and 20 cm depth was
governed by the molecular heat transport. Therefore, the
heating and cooling rates of Ts were always lower than
for Ta. Higher Ta and Ts 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
Ta and Ts 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.