Net radiation balance for two forested slopes on opposite sides of a valley

Abstract

Measurements of the net radiation balance of two forested sites on the opposite slopes of a valley in south-western Germany, made over 3 years, are presented in this study. Radiation sensors were mounted horizontally on two measurement towers above two beech stands. The direct part of the measured short-wave incoming radiation was adjusted according to the slope's angle to convert horizontally measured radiation data into surface-parallel radiation fluxes. During periods when contemporaneous measurements of slope-parallel and horizontal radiation fluxes were available, the calculation of surface-parallel radiation fluxes from the horizontally recorded net radiation components were compared with measured values. The net radiative fluxes parallel to the slopes were calculated for a period of 36 months and analysed. Results show that the different aspects of both sites cause significant differences of the net radiation balance. In June, when the elevation of the sun is highest, incoming solar radiation K downward arrow received on the NE-slope was 9% lower than K downward arrow received on the SW-slope. During the winter months, the differences were much greater and incoming solar radiation to the NE-slope was 50% of that to the SW-slope. Due to the differing solar irradiance, net radiation fluxes were significantly higher on the SW-slope than on the NE-slope. For long-wave radiation only small differences between both slopes could be found. Since radiative fluxes determine the energy balance and hence the microclimate and water balance of a forest stand, these differences in the net radiation balance between the slopes are important for the vegetation.

Responses of Abies alba seedlings to different site conditions in Picea abies plantations

“…This suggestion is supported by the study of Kantor (2001), which recommended regenerating fir by regeneration under a shelterwood or regeneration by strips of about 40 × 20 m. According to this author, regeneration by strip is, providing conformance with the environmental requirements of fir, operationally more suitable, because is it simpler and easier. Regenerating by strip, it is necessary to plan the exposure and shape of the felling in such a way that the seedlings are shaded for the most of the day (Kantor 2001;Holst et al 2005;Hu et al 2010). In addition, Kantor (2001), recommended ensuring a long regeneration period with differential spatial arrangement in the newly established stands.…”

Tree- and Stand-Level Thinning Effects on Growth of European Beech (Fagus sylvatica L.) on a Northeast- and a Southwest-Facing Slope in Southwest Germany

“…The research sites are not more than 1000 m apart. The regional climate in the area is semi-continental, with mean annual air temperature of about 7.0 °C, and annual precipitation of 900 mm (over the period [30,31]. Rainfall does not vary significantly across the valley [32].…”

Downscaling regional climate data to calculate the radiative index of dryness in complex terrain

“…et al (2003) found that slope orientation was the most important variable because of its strong impact on the shortwave radiation which comprises the main source of incoming energy. The changing position of the sun with seasons means that the effect of slope orientation is largest during the winter and smallest during the summer months (Holst et al 2005;Kumar et al 1997;Lambert and Roberts 1976). In this study, the effect of seasonal variability was incorporated by modelling topographic effects for each hour of the day in a year using long-term average input from BoM to describe the proportion of diffuse radiation.…”

“…Net radiation in the southeast Australian region and other mid latitude (temperate) regions is particularly sensitive to the effect of topography because that is where the effect of slope orientation on incoming radiation is strongest (Holland and Steyn 1975;Holst et al 2005). In these regions it is therefore important that research in ecohydrology and geomorphology are placed into the context of the net radiation (energy availability) and aridity (water availability).…”

“…At mid-to high latitudes, the slope orientation can have large effects on R n with implications for water and energy availability at small scales (Moore et al 1993). The resulting heterogeneity in ecological, hydrological and geomorphic processes at these small scales can be important sources of uncertainty when modelling catchment processes (Badano et al 2005;Band 1993;Bradstock et al 2010;Holland and Steyn 1975;Holst et al 2005;Nunez 1980). Net radiation in complex terrain can be modelled by combining point data from weather stations with equations that incorporate the effects of elevation, surface geometry and atmospheric attenuation of incoming radiation (Moore et al 1993;Running et al 1987;Wilson and Gallant 2000).…”