Microclimate within beech stands?part II: thermal conditions

Abstract

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.