Relationship between Tree Density and Grass Dry Matter Yield in a Southern African Savanna

The investigation was carried out on a densely wooded area in the Mopani savanna of South Africa. Seven plots were subjected to different intensities of tree thinning, ranging from a totally cleared plot (0 %) to plots thinned to the equivalent of 10 %, 20 %, 35 %, 50 % and 75 % of the leaf biomass of a control plot (100 %). The grasses responded positively to the tree thinning in terms of total dry matter yield. The yields between tree canopies were generally of the same order or higher than under tree canopies, with the yields where trees have been removed initially the highest. At high tree densities, yields differed little between seasons of varying rainfall. No quantitative advantages of C. mopane trees on the grass layer could be established, and the highest grass DM yields were recorded in plots where all trees were removed. The relationship between grass DM yield and tree density (expressed as Evapotranspiration Tree Equivalents ha-1) was curvilinear, best described by the exponential regression equation

The Influence of Tree Thinning and Tree Species on the Dry Matter Yield of Grasses of a Bush Encroached Semi-Arid Savanna in South Africa

The Acacia erubescens-Combetum apiculatum dominated savanna of South Africa is water-limited and an increase in woody plant abundance suppresses the grasses. This is the major reason why thinning or total clearing of all woody plants is often considered by landowners. The objectives of this study were to investigate the influence of intensity of tree thinning and tree species on grass yields in a semi-arid South African savanna

Grazing Impacts on Rangeland Condition in Semi-Arid South-Western Africa

The savannah biome, consisting of a dense herbaceous layer and a relatively open woody layer in competitive balance, constitutes 64% of the land surface of Namibia, an arid country in south-western Africa, and is used mainly for extensive cattle and sheep ranching. About half of the savannah area is affected by dense to moderately dense bush-thickening, resulting in a ten-fold decrease in the rangeland’s grass-based carrying capacity and a concomitant loss in meat production of about US$115 million per year (De Klerk, 2004). Bushencroached areas typically have densities \u3e 2 000 bushes/ha with \u3e 90% belonging to a single species. High grazing pressure by specialist grazers, such as domestic cattle, is often blamed for rangeland degradation. There is an urgent need to understand the dynamics of bush encroachment and devise grazing strategies to contain it

Investigation of the Domain Wall Fermion Approach to Chiral Gauge Theories on the Lattice

We investigate a recent proposal to construct chiral gauge theories on the lattice using domain wall fermions. We restrict ourselves to the finite volume case, in which two domain walls are present, with modes of opposite chirality on each of them. We couple the chiral fermions on only one of the domain walls to a gauge field. In order to preserve gauge invariance, we have to add a scalar field, which gives rise to additional light mirror fermion and scalar modes. We argue that in an anomaly free model these extra modes would decouple if our model possesses a so-called strong coupling symmetric phase. However, our numerical results indicate that such a phase most probably does not exist. ---- Note: 9 Postscript figures are appended as uuencoded compressed tar file.Comment: 27p. Latex; UCSD/PTH 93-28, Wash. U. HEP/93-6