Patch area and current coffee management determine woody plant diversity in patches of semi-forest coffee embedded in an agricultural matrix

Effective conservation of biodiversity in patches of (semi-) natural vegetation is dependent on an understanding of the influence of management as well as spatial and temporal factors. In southwestern Ethiopia coffee generally grown under a rather dense layer of indigenous trees (so called semi-forest coffee - SFC) often in patches embedded in an open agricultural landscape. The aim of the study was to disentangle what governs the variation in species richness of woody species among such patches. We collected data on species and possible explanatory factors in 40 × 40 m plots centered in 40 SFC patches, measured the patch area for 1987 and 2013, and the amount of surrounding SFC-area for each patch. We recorded the number of coffee stems and the level of disturbance caused by slashing of the understory vegetation. Species richness of large coffee shade trees (>20 cm in diameter) was higher in larger patches with even slightly better fit of the statistical models when the historical area was taken into account. However, most species of large trees also occurred as seedlings showing that there is still a potential to conserve these species in the patches. Coffee management negatively affected the richness and density of woody species, especially in the intermediate size class (1.6-20 cm diameter). Disturbances accompanying coffee management such as slashing of the ground vegetation also negatively affected tree seedling density as well as species richness. There was no effect of connectivity on species richness. Based on the combination of these results we conclude that small patches of semi-forest coffee had fewer species of large trees, not because of a lack of tree seedlings, but probably because of differentiated local extinctions, perhaps during the time when the species were intermediate sized. To maintain the species richness of large trees in semi-forest coffee patches, the sites need to be actively managed.