Development of vaporization process from young stands of Norway Spruce and European Beech after snow breakage

The extreme disturbance of the forest environment in the young experimental spruce stand in the Orlické Hory Mts after the snow breakage disaster in the winter of 2005/2006 became the impulse for the present study. 98% spruce trees were affected, the stand density decreased from 1550 to 950 trees per ha, the needle foliage of the stand was reduced to about 40%, and the stand canopy was markedly disturbed. The investigation consisted of two methodical procedures: the assessment of evapotranspiration of the forest stands (ET) based on continuous measuring of the water content in the root zone of the soil profile, and intermittent measuring of evaporation from the soil surface including the ground vegetation (Es). Comparative investigation was simultaneously done in a young experimental beech stand with minimum disturbance. ET totals (evaporation from the soil surface and ground vegetation Es + transpiration of trees T) were comparable in both stands (200 to 235 mm during the growing season). Until 2006, ET was � 10% higher in the spruce stand, whereas in 2007, ET was 10% higher in the beech stand. An extremely high increase of the soil surface evaporation (Es) was observed in a gappy spruce stand. Immediately after the disaster, maximum daily totals of evaporation ranged from 1.5 to 2.0 mm in the spring and summer 2006, while in the beechstand they reached half these values. In the following year 2007, with gradual weeds infestation of the stand gaps, whose cover extended to 80% in the summer and autumn, the values of Es in the spruce stand reached up to 3 mm per day, on warm summer days being on the level of the weed-infested clear felled area. In the same days, evaporation in a fully closed beech stand was usually 3 to 4 times lower. The evaporation from the soil surface and ground vegetation evidently substituted the reduced transpiration of the spruce broken canopy, if ET total did not change significantly.