Epiphytic orchid diversity found on trees and shrubs in coffee cultivated Afromontane rainforest, SW Ethiopia

The moist evergreen Afromontane forest of SW Ethiopia has become extremely fragmented and most remnants are intensively managed for cultivation of coffee (Coffea arabica). We investigated the distributions of epiphytic orchids in shade trees and their understory in forests with contrasting management intensity to determine biodiversity losses associated with coffee cultivation and to determine the capacity of coffee shrubs to act as refugia for orchid species. We studied epiphytic orchids in managed forests and natural forests and recorded orchid diversity and abundance in different tree zones of 339 trees and in the understory. Coffee management was associated with a downward shift of orchid species as orchid species were occurring in significantly lower tree zones in managed forest. The number of shrubs in the understory of managed forest was not higher than in natural forests, yet orchid abundance was higher in the understory of managed forests. Local extinctions of epiphytic orchids and species losses in the outer tree zones (a contraction of habitat) in managed forests are most likely driven by losses of large, complex-structured climax trees, and changes in microclimate, respectively. Coffee shrubs and their shade trees in managed forests are shown here to be a suitable habitat for only a limited set of orchid species. As farmers continue to convert natural forest into managed forest for coffee cultivation, further losses of habitat quality and collateral declines in regional epiphytic orchid diversity can be expected. Therefore, the conservation of epiphytic orchid diversity, as well as other components of diversity of the coffee forests, must primarily rely on avoiding coffee management intensification in the remaining natural forest. Convincing farmers to keep forest-climax trees in their coffee forest and to tolerate orchids on their coffee shrubs may also contribute to a more favorable conservation status of orchids in Ethiopian coffee agroecosystems.埃塞俄比亚西南部的湿润常绿非洲山地林（moist evergreen Afromontane forest）已呈现高度破碎化，绝大多数残存林分均被集约经营，用于种植阿拉伯咖啡（Coffea arabica）。本研究针对经营强度存在差异的林分，调查了附生兰科植物（epiphytic orchids）在遮荫树（shade trees）及其林下层（understory）的分布特征，旨在明确咖啡种植活动所引发的生物多样性损失，并评估咖啡灌木作为兰科植物物种避难所的潜力。我们在经营林与天然林中开展附生兰科植物调查，记录了339株树木不同垂直树带（tree zones）以及林下层的兰科植物多样性与个体丰度。研究发现，咖啡经营与兰科植物分布的向下偏移存在显著关联：经营林中的兰科植物显著集中于更低的树带位置。经营林林下的灌木数量并未高于天然林，但经营林林下的兰科植物丰度却显著更高。经营林中附生兰科植物的局域灭绝，以及树木外层树带的物种流失（栖息地收缩现象），其主要驱动因素分别为大型复杂结构顶极乔木（climax trees）的消失，以及微气候改变。本研究结果表明，经营林中的咖啡灌木及其配套遮荫树仅能为有限类群的兰科植物提供适宜栖息地。随着农户持续将天然林改造为咖啡种植经营林，栖息地质量的进一步退化与区域附生兰科植物多样性的附带下降或将不可避免。因此，若要保护附生兰科植物多样性及咖啡林的其他生物多样性组分，首要举措需避免在残存天然林中强化咖啡经营。此外，说服农户在咖啡林中保留森林顶极乔木（forest-climax trees），并容忍咖啡灌木上的兰科植物生长，或可改善埃塞俄比亚咖啡农业生态系统（coffee agroecosystems）中兰科植物的保护现状。