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.在埃塞俄比亚西南部，湿润常绿非洲山地森林（moist evergreen Afromontane forest）已发生极度破碎化，绝大多数残存林分均被集约经营用于阿拉伯咖啡（Coffea arabica）种植，对生物多样性（biodiversity）与生态系统功能（ecosystem functioning）造成了显著负面影响。鉴于附生兰科植物（epiphytic orchids）可作为森林质量的潜在指示物，同时也是整体森林生物多样性的替代指标，本研究针对森林经营与森林破碎化对附生兰科植物多样性的影响展开了系统评估。我们分别从大型与小型森林残存斑块中选取经营林地，并将其附生兰科植物多样性与未受干扰的天然完整林分进行对比分析。本研究采用绳索攀爬技术，共调查了339株冠层树木（canopy trees）。研究结果显示，从天然未破碎化森林、经经营的大型森林斑块到经经营的小型森林斑块，附生兰科植物的物种丰富度逐步降低，群落组成亦发生显著改变。这表明森林经营与森林破碎化均会导致附生兰科植物的多样性流失。咖啡种植经营中常见的大型冠层树木移除行为，以及伴随森林破碎化出现的边缘效应（edge effects），极有可能是引发物种流失与群落组成改变的核心诱因。尽管部分濒危兰科物种（endangered orchid species）即便在最小的森林残存斑块中仍可存续，但相较于小型经营林地，大型经营森林斑块更适宜作为附生兰科植物的保护栖息地。本研究最终证实，尽管遮荫咖啡种植（shade coffee cultivation）被视作近自然经营模式，并被推广为兼具生物多样性保护效益的实践方式，但其所能提供的附生兰科植物保护效益仍无法与未受经营的湿润常绿非洲山地森林相媲美。