The Orchidaceae, at more than 26,000 species distributed across all inhabited continents, is one of the largest angiosperm families. Made up of 70% epiphytes, the family is most diverse in the tropics, though terrestrial species occur in temperate regions as well. Orchids face high levels of threat from habitat destruction, over-collecting, and climate change, among other issues, and feature prominently on the threatened plant species lists of a number of countries. Morphologically, orchids are unique in their combination of unusual traits, including a single stamen fused with the pistil to form a structure known as the column, pollen grains bound in large masses called pollinia, and minuscule ‘dust seeds’ that lack an endosperm. On an ecological level, orchids have still more unique facets that can complicate conservation efforts.
In a new review published in Annals of Botany, lead author Ryan D. Phillips and colleagues delved into these aspects of orchid biology, exploring how they can leave orchids at risk, how they must be accounted for when planning conservation strategies, as well as some specific steps that could be taken to improve orchid conservation outcomes.
Orchids often display highly specialized pollination, depending on only one or a few different pollinator species. This leaves the plants vulnerable to any disruption amongst their preferred species, as well as upping the difficulty of translocations of communities at risk, since the pollinator must be present in the new location. Orchids also frequently display a very limited fruit set, but with very high numbers of seeds per fruit. While this makes many seeds available for experimental plantings, it results in low genetic diversity, since so many seeds are fathered via so few pollen donors. Mycorrhizal dependence is another facet of orchid biology that presents difficulties. Most orchids require symbiosis with an acceptable fungal partner in order to germinate and until the first leaves appear. Though many orchids associate with a range of fungal species, some are highly specialized to just one or a few, and this information often isn’t known on a species-to-species basis.
How are these features best addressed for conservation purposes? “The highest priority for the preservation of biodiversity is preserving habitat. It is much more effective to preserve habitat in the first place than to engage in intensive interventions once species have become threatened,” Phillips says. However, when translocations due to habitat loss become a necessity, the conditions required to allow translocated orchids to thrive in a new location must be considered. Pollinators must be identified and their range determined so pollination can take place in the new community. Landscapes must be managed in such a way that pollinator populations are supported, such as considering habitat fragmentation and pesticide use. Similarly, fungal symbionts need to be identified and their presence ensured at new sites, while being aware that the fungi required for germination may be a subset of those found in the mature plant, or may not be present at all. The required fungi are often widespread in the soil, but patchy, and germination sites close to adult populations can increase success, as can adding rotting wood to the area.
The state of orchid conservation is one that varies widely by region, as does the degree of habitat loss. Phillips points out that money and scientific knowledge related to conservation tend to be concentrated in temperate regions, while the greatest diversity of orchids lies in the tropics, though he is hopeful that many techniques developed in temperate regions will be broadly applicable to different species. “Many of the countries with highest orchid diversity have comparatively little funding for research of any kind, including conservation,” he says. “While orchids are well known in the wider community, contrary to what some assume, orchid conservation is not well funded in the majority of cases.” He adds that there is a large contribution being made to the effort by community volunteers. “International collaborations are common in orchid biology, but it is a recurring theme in conservation in general that the best outcomes are achieved when conservation is driven by locals.”