III. Buchbesprechungen

Ohne Zusammenfassung     

Über eine Fledermausplage

Ohne Zusammenfassung Mit 1 Abbildung.     

Effect of stocking density on vegetation and animal performance within the semi-arid shrublands of the Karoo,South Africa

As the primary land use in the Karoo, extensive small-stock farming contributes significantly towards the agricultural economy of the region. However, the sustainability of this practice has been questioned for many years. This led to the establishment of a long-term stocking-density trial in 1988 at the Carnarvon Research Station. The trial was designed on a three-camp rotational grazing system under four stocking densities (8, 7, 5.5 and 4 ha SSU^–1). Following continuous treatment over 28 years, the results from a once-off assessment in February 2016 portrayed no significant differences between treatments with regard to plant height, cover, species diversity, ecological and grazing index scores. Animal production varied among treatments where the mean production per hectare was found to be the highest under the high stocking-density treatment. Due to the absence of historical data, the results from this study are not conclusive with regards to changes in the vegetation dynamics over time and therefore does not lend itself to making conclusions concerning stocking densities. It can, however, be concluded that the vegetation of the Western Upper Karoo is remarkably resilient to the perceived higher stocking densities set at the time, on condition that an appropriate grazing management strategy is applied.     

Vom Wesen waldbaulicher Arbeit heute und morgen

Summary The crisis of classical silviculture in the middle-european sustained yield forestry becomes evident—above all—in the large discrepancy between scientific findings and practical management. Numerous inhibiting factors are to be held responsible for this: lack of a silivcultural basis for combined objectives in the management of productive and social forests, forest-technical development aid from the boreal wood-exploitation areas, the modernization of forest management being too onesided oriented to industry, a lack of professional improvement, sociological problems as a denaturation of man by technology and economy etc. An integral silviculture, based on ecological fundaments and following a free style, must lead to an optimization of interdisciplinary conflicts of objective under the aspect of long-term objectives. The comprehensive life-work of the man whose jubilee we celebrate has readied the way to a solution.      

Coherent response of a group of plantation-grown Scots pine trees to wind loading

Wind-induced motion of 29 neighbouring trees growing in a Scots pine plantation was measured over the period 14 March to 24 March 2008. The bi-orthogonal decomposition (BOD) of the complex tree motion field into a limited number of spatio-temporal modes provided the basis for the analysis of the response behaviour to wind excitation of the group of sample trees. It is shown that the first BOD-mode was the most energetic and differed from all other BOD-modes. The BOD-results as well as the results from wavelet analysis of the temporal eigenvectors of the BOD-modes demonstrate that two concomitant low-frequency components in the streamwise wind velocity component stimulated coherent response of the sample trees at the tree group level. However, in the range of the wind speed measured close to the top of the Scots pine forest canopy (hourly mean wind speed values lower than 6 m s⁻¹), the wind loads associated with these low-frequency airflow structures were too low to harmonise the motion of the sample trees completely. It is shown that instantaneous single tree responses to wind excitation were highly irregular in magnitude and direction. Results from Fourier and wavelet analysis demonstrate that sway in the first mode dominated the wind-induced sway behaviour at the tree level.