Phytosociological study of arable weed communities across small scale ag-ricultural landscape in Swaziland

Abstract

Aims: Using a multi-criteria evaluation comprised of fidelity, cluster, and additive partitioning analyses, this work described the composition and diversity of arable weed communities in five agro-ecological regions of Swaziland. Spatial scales at which diversity components (a, and y) were most relevant in describing weed vegetation were studied. Study area: Swaziland. Methods: The data set for analyses was obtained using both multi-stage systematic and random sampling of 117 small scale farmers' fields. The affinities of 40 weed species identified in the study to different zones were determined using phi coefficient of association, a statistically defined measure of fidelity. Agglomerative hierarchical cluster analysis was based on standardized species ranks from a consensus of phi, indicator value index, and relative abundance index. The Euclidean distance measure and Ward's method for group linkage were used to yield cluster solutions for each region. Species diversity was expressed as the proportional contribution to diversity at three scale levels, i.e. plot, field, and region, using the hierarchical additive partitioning approach. Results: Eighteen species were diagnostic to particular regions amongst which only two species appeared in two contiguous regions to which they were characteristic. The weed vegetation was characterised by three to four clusters with a group of taxa co-occurring in the same cluster across the five regions. A major part of weed diversity was mainly explained by beta-diversity at regional scale (35.0-67.8%) than between fields (12.0-15.0%) or sampling plots (0.1-2.8%). Diversity within fields (alpha-diversity) was between 5.0 and 8.2% in the five regions. Conclusion: The nested approach adopted where weed species were described and enumerated individually, in clusters, and, at different spatial scales could inform subsequent work towards diversification and scale of weed management approaches or tools in small scale agriculture.