Impact of agricultural intensification on biodiversity and secondary succession in the Mid-Zambezi Valley, Northern Zimbabwe

Abstract

In this thesis, the impact of woodland clearing, cultivation intensity and fallowing on tree species diversity, physiognomy and dominance was tested in the semi-arid mid-Zambezi valley, northern Zimbabwe. This study further tested the impact of agriculture on arthropod biodiversity using butterflies in the genus Charaxes (Lepidoptera: Nymphalidae) and beetles in the subfamily Cetoniinae (Coleoptera: Scarabaeidae). This study also investigated vegetation dynamics within recovering fallow areas. Results showed that, in both intensified and less intensified agricultural areas, conversion of natural woodland areas to cropped fields result in rapid decrease in tree diversity at field level, while at landscape level agricultural activities do not affect woody species diversity, at least in the short term. Instead, through selective cutting down of trees and subsequent crop cultivation negative impacts of woodland conversion is on tree physiognomy and dominance. At a higher trophic level, results showed that woodland clearing resulted in a decrease in abundance and loss of diversity of fruit-feeding butterflies of the genus Charaxes and beetles of the subfamily Cetoniinae with loss recorded in areas homogeneous intensively cultivated areas. Furthermore, results showed that, vegetation dynamics within fallow areas area characterised by a change in floristic composition with high rates of above-ground biomass accumulation driven by dominance of invasive species such as Acacia tortilis subsp spirocarpa. All sets of results in this study indicated that any efforts to conserve biodiversity within agricultural landscapes in the mid-Zambezi valley may have to focus on implementing an agricultural paradigm that maintains a mosaic of different land-use units, each in a different phase of clearance-cultivation-abandonment-recovery-clearance cycle.