Structure and diversity of the dry woodland savanna of northern Namibia

Abstract

The dry woodland savannas are of significant importance for the regional economy as they provide the resources including food, building material and fuel. The factors that affect the vegetation may be divided into two groups. On the one hand are the 'determining factors', i.e. Those that dictate the potential vegetation structure. These are primarily those factors that affect the soil moisture regime. On the other hand are the 'modifying factors' that influence the current vegetation to cause a structural change. These are human activity such as land use, grazing management, timber exploitation and the collection of veld foods. A further, very important factor, is the influence of fire. The plant species that occur in the dry woodland savanna have adapted to various degrees to the varying factors, so that the composition of a woodland stand may vary with the frequency and intensity of an influence. It is important that the natural disturbances continue to influence the woodland stands, to maintain a healthy population structure. In this way it is possible to extract some of the trees without endagering the tree population. To determine how many trees may be removed from the various diameter classes in a stand, a guide curve is established using the negative exponential function. The guide curve suggests a stable, sustainable population structure. The modifying factors may also result in a spatial differentiation of species and diameter classes. An index is suggested here that will quantify the degree of interspersion of tree attributes as well as a norm which may assist in the interpretation of field measurements.