Epiphytic orchid diversity and community composition in managed and natural moist evergreen Afromontane forest in SW Ethiopia

In SW Ethiopia, the moist evergreen Afromontane forest has become extremely fragmented and most of the remnants are intensively managed for coffee cultivation (Coffea arabica), with considerable impacts on biodiversity and ecosystem functioning. Because epiphytic orchids are potential indicators for forest quality and a proxy for overall forest biodiversity, we assessed the effect of forest management and forest fragmentation on epiphytic orchid diversity. We selected managed forest sites from both large and small forest remnants and compared their epiphytic orchid diversity with the diversity of natural unfragmented forest. We surveyed 339 canopy trees using rope climbing techniques. Orchid richness decreased and community composition changed, from the natural unfragmented forest, over the large managed forest fragments to the small managed forest fragments. This indicates that both forest management and fragmentation contribute to the loss of epiphytic orchids. Both the removal of large canopy trees typical for coffee management, and the occurrence of edge effects accompanying forest fragmentation are likely responsible for species loss and community composition changes. Even though some endangered orchid species persist even in the smallest fragments, large managed forest fragments are better options for the conservation of epiphytic orchids than small managed forests. Our results ultimately show that even though shade coffee cultivation is considered as a close-to-nature practice and is promoted as biodiversity conservation friendly, it cannot compete with the epiphytic orchid conservation benefit generated by unmanaged moist evergreen Afromontane forests.

埃塞俄比亚西南地区的湿润常绿非洲山地林（moist evergreen Afromontane forest）已发生高度破碎化，多数剩余斑块被集约经营用于阿拉伯咖啡（Coffea arabica）种植，对生物多样性与生态系统功能造成显著影响。鉴于附生兰科植物（epiphytic orchids）可作为森林质量的潜在指示物与整体森林生物多样性的替代指标，本研究评估了森林经营与森林破碎化对附生兰科植物多样性的影响。研究选取了大小型森林剩余斑块中的经营林分，并将其附生兰科植物多样性与天然未破碎化森林的多样性进行对比；同时采用绳索攀爬技术，对339株冠层树木开展了调查。从天然未破碎化森林、大型经营森林斑块到小型经营森林斑块，兰科植物物种丰富度逐渐降低，群落组成亦发生相应改变，这表明森林经营与破碎化共同导致了附生兰科植物的物种丧失。咖啡种植典型经营模式下的大型冠层树木移除，以及森林破碎化伴随的边缘效应，均可能是物种丧失与群落组成改变的关键诱因。尽管部分濒危兰科植物仍可在最小的森林斑块中存续，但相较于小型经营林，大型经营森林斑块更利于附生兰科植物的保护。本研究结果最终表明，尽管遮荫咖啡种植被视为近自然经营模式，并被宣传为有利于生物多样性保护，但其在附生兰科植物保护方面的效益仍无法与未受干扰的湿润常绿非洲山地林相媲美。