Abstract
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.
Highlights
Habitat loss and fragmentation have been recognized as major conservation threats to terrestrial biodiversity (Rands et al, 2010; Haddad et al, 2015; Martín-Queller et al, 2017)
Apart from the fact that reduced population sizes in smaller patches negatively influence species persistence (Shaffer 1981; Wilsey et al, 2005), decreases in forest patch size lead to reductions in tree basal area, and a lower recruitment of seedlings (Benitez-Malvido 1998)
For mature trees and saplings, when based on abundance, AIC-based multimodel inference shows that the species diversity and the Shannon index correlated positively with church forest patch area and with the presence of natural forests in the surrounding landscape, and negatively with the distance to Bahir Dar
Summary
Habitat loss and fragmentation have been recognized as major conservation threats to terrestrial biodiversity (Rands et al, 2010; Haddad et al, 2015; Martín-Queller et al, 2017). An inhospitably matrix can hamper dispersal and lead to reduced connectivity among remaining fragments, negatively affecting metacommunity structure as diminished recolonization increases species extinction rates. Such landscape-level processes may be especially important for tropical forests, as more than 90% of tropical woody plant species depend on zoochory (Bregman et al, 2016) while population persistence of seed-dispersing animals codepends on the quality of the surrounding matrix as a (secondary) habitat resource (Antongiovanni and Metzger 2005; Kennedy et al, 2011)
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