WEED SPECIES STRUCTURAL AND FUNCTIONAL COMPOSITION OF OKRA FIELDS AND FIELD PERIPHERY UNDER DIFFERENT MANAGEMENT INTENSITIES ALONG THE RURAL-URBAN GRADIENT OF TWO WEST AFRICAN CITIES

Abstract

In urban and peri-urban agricultural production systems of Sub-Saharan African cities, diverse and functional complex weed communities may help to maintain biodiversity and ecosystem services and therefore indirectly support crop performance. However, effects of agricultural intensification and urbanisation on important weed diversity in the West African region had received so far little attention, although in Burkina Faso and Ghana up to 90 per cent of the population depends on agriculture as a main source of income generation. Hence, our research focussed on the analysis of changes in weed assemblages’ structure and function of okra fields that were cultivated under different management intensities and were embedded into the rural, peri-urban and urban environment of two West African cities: Ouagadougou (Burkina Faso) and Tamale (Ghana). We found a strong relationship between gender and market orientation of okra cultivation. Market orientation of okra farmers was also a major driver in shaping weed species assemblages and led to the development of a distinct weed assemblage in urban areas that even showed higher diversity in weeds’ function. Morphological plant traits (life form, seed properties) were most affected by agricultural practises; distribution pattern of ecological traits (seed dispersal mode, pollination vector) seemed to be influenced additionally by environmental character- istics with less entomophilous but more ornithochorous weed species on okra fields within urban areas. Our results revealed that the management of okra was highly variable and that this variation was influenced by farmers’ socioeconomic background leading to changes in soil properties. These in turn may alter the functional diversity of beneficial weed communities beyond changes in species richness by potentially harming the provisioning of ecosystem services such as pest control and pollination.