Small forest patches in Ethiopian highlands uniquely support high plant biodiversity

Habitat fragmentation is one of the main causes of the global loss of plant biodiversity. It is also one of the major challenges in Ethiopia, where fragmented forest patches of different sizes have been observed. These patches of forest, especially in the highlands of northern Ethiopia, are mainly confined to churches. These remnant forest patches have long been said to have negative impacts (habitat amount hypothesis). Recently, however, there is evidence that these small patches of remnant forest may harbour more species than relatively large patches of the same area. We tested this hypothesis in the remnant church forests of the Ethiopian highlands using different plant growth forms. Ten church forests of different sizes were selected in which transects were established from the forest edges to the interior. A total of 56 20 × 20 m plots were used for plant sampling. All trees, shrubs and herbs within the plots were recorded, collected and identified. We found that the effects of forest fragmentation on plant diversity, abundance and composition varied with plant growth forms. In contrast to the habitat amount hypothesis, small forest fragments were found to support more tree species than relatively large forest fragments, suggesting the role of small forest fragments in maintaining species diversity. We found that soil moisture changes with fragment size but has no significant effect on plant abundance and diversity of plant growth forms. Our results indicate that a shift in conservation priorities may be needed to recognize the value of small fragmented patches of forest for biodiversity conservation, as a lack of protection of small patches of forest can lead to high cumulative impacts on biodiversity loss.