Potential Challenges of Climate Change to Orchid Conservation in a Wild Orchid Hotspot in Southwestern China

Abstract

Southwestern China including Guangxi Province is one of nine world hotspots for orchid. Warming in the region in the past century was around 0.5°C, slightly lower than the global average of 0.7°C, while rainfall has remained the same. It is projected that the warming trend will continue for the next two centuries, while precipitation will increase slightly, and soil moisture level will decrease. We identify a number of threats due to climate changes to orchid community in the Yachang Orchid Nature Reserve in Guangxi (hereafter refer to as Yachang Reserve), a good representative of the region. Firstly, decreased soil moisture is likely to have a negative effect on growth and survival of orchids, especially terrestrial and saprophytic ones. Sixty eight (50%) orchid species in the Yachang Reserve are in this category. Secondly, the greater majority of the orchids in Yachang Reserve (72%) have populations on or close to the limestone mountain tops. These populations are likely to shrink or even become extinct as the warming continues because they have no higher places to which they are able to migrate. Natural poleward migration is unlikely for these populations because of the complex terrain, small size of the reserve and human-dominated surroundings. Species with narrow distributions (14%) and/or small population sizes (46%) will be the most vulnerable. In addition, populations represent the southern limit of the species (24%) are also prone to local extinction. Thirdly, extreme rainfall events are projected to occur more frequently, which can exacerbate erosion. This may impact orchid populations that grow on steep cliffs. Fifty seven species (42%) of the orchids in Yachang have cliff populations. Fourthly, the majority of orchid species have specialized insect pollination systems. It is unknown whether the change or lack of change in plant phenology will be in synchrony with the potential phenological shifts of their pollinators. Fifty four (40%) orchid species in Yachang Reserve flower in the spring and are potentially subject to this threat. Finally, mycorrhizal fungi are vital for seed germination for all orchids and important for post-seedling growth for some species. Yet there is a lack of knowledge of the nature of mycorrhiza on all orchids in the region, and little is known on the responses of these vital symbiotic relationships to temperature and soil moisture. Overall, 15% of the orchid species and a quarter of the genera bear high risk of population reduction or local extinction under the current projection of climate change. While studies on predicting and documenting the consequences of climate change on biodiversity are increasing, few identified the actual mechanisms through which climate change will affect individual species. Our study provides a unique perspective by identifying specific threats to a plant community.