Résumé
Forest fragmentation is globally pervasive but especially severe in tropical forests, as exemplified by the state of Afrotropical montane forests in Ethiopia, where remnant forests almost exclusively exists as small, isolated fragments centered around churches, forming networks of partially intact ‘habitat islands.’ Church forests deliver ecosystem services such as forest products and erosion control, and are considered a benchmark for assessing forest biodiversity quality. However, safeguarding church forest integrity necessitates a better understanding of the factors determining their biodiversity and community structure. Therefore, we surveyed a network of church forests southeast of Lake Tana to assess factors explaining their tree species richness and composition. We found that the 24 church forests studied here represent about 20% of the ca. 270 tree species that occur in tropical northeast Africa. All surveyed forests however face strong extinction debts, with five tree species at risk of completely disappearing from the region and many more species only regenerating in a limited number of church forests. Church forest integrity partially reflected the anthropogenic pressure on the area, as forest regeneration tended to be stronger in fenced church forests. Seedling abundance depended on the local presence of large, mature conspecific trees and on the geographic distance to potential source populations of seeds, strongly suggest that metapopulation dynamics likely are important. We conclude that church forest conservation and minimizing further degradation of the landscape matrix are needed to help sustaining the ecological and socioeconomic potential of this unique network of remnant forests.