Die potensiaal en dinamika van Acacia karroo indringing, verdigting en afsterwing op die BC-landtipe

Abstract

The occurrence of ligneous types has increased radically in the grassland biome of South Africa in the course of the past decades. Thousands of hectares of initially high potential grass veld have become useless for grazing as the result of the invasion and increase of the trees. Although the increase can be regarded as a secondary cause of veld deterioration, it has far-reaching ecological and economical implications. This study is an attempt to determine the reaction of A.karroo in veld degradation and to incorporate the findings in the exciting degradation model for the BC-land type for two topographical positions, viz. pediments and mid-slopes, in the 550-600 rainfall region. A gradual increase was found in the A.karroo totals per hectare in veld that was slightly utilized to under-utilized. This increase was found to continue in the second domain up to a point where veld degradation becomes so severe that conditions for the establishment and survival of A.karroo become restricted. Tree totals diminish in the third domain of attraction. Different reactions of A.karroo were encountered in the different topographical positions. Both the increase and the dying-off occur at an earlier point during veld degradation on the mid-slopes, while the pediments are able to sustain a higher number of trees per hectare. A further distinction was made between the different soil types of the various topographical positions, as well as of the height classes of trees on the same soil type. It would appear that soil types differ in sensitivity regarding the establishment and survival of A.karroo , with the clay percentage of the soil being a determining factor in the height classification distribution of the trees. Accurate historical background regarding prior management practices is essential to explain the causes and the effects of the invasion, increase and dying-off of A.karroo in the grassland biome.