Abstract
The management of endangered or threatened plant species is difficult if protocols are not developed to propagate species for the purpose of restoration or the enhancement of existing populations. The management of endangered and threatened orchids is especially difficult because of the obligate interactions between orchids and orchid mycorrhizal fungi. Isotria medeoloides is a federally threatened forest-dwelling orchid species with a wide distribution in eastern North America. Seeds have not been successfully germinated and current management is based primarily on using subcanopy thinning to increase light in areas where monitoring demonstrates that populations are declining. We report the results of long-term monitoring efforts, canopy thinning, and orchid mycorrhizal fungus abundance studies at two locations in Virginia. The declining populations responded positively to the experimental and natural thinning of the canopy. At one site, the response was the result of understory canopy thinning. At the second site, the response was due to the natural death of a canopy tree. In light of the dramatic increase in fungal abundance following death of the canopy tree, we propose the Fungal Abundance Hypothesis as an additional approach to the management of endangered plant species. The removal of canopy trees in or adjacent to Isotria populations results in an increase in dead belowground biomass (i.e., roots of the dead canopy tree) that provides substrates for microbial growth, including orchid mycorrhizal fungi, that benefit Isotria.
Highlights
The management of threatened plant species requires knowledge about the ecology of the species, including the monitoring of the species and the environmental factors in ecosystems where the species occur [1]
We previously found that the soil adjacent to plants that emerged from dormancy had more orchid mycorrhiza DNA compared to the soil adjacent to plants that had not emerged from dormancy [29]
In view of the results of our DNA comparison, we propose that the abundance of orchid mycorrhizal fungi in the soil adjacent to orchids should be considered an element of the management of native orchids
Summary
The management of threatened plant species requires knowledge about the ecology of the species, including the monitoring of the species and the environmental factors in ecosystems where the species occur [1]. Approaches to the management of orchids vary from protecting their habitat, especially global hot-spots with a high species diversity [4,5], to propagating orchids from seed for restoration purposes [3]. The management of existing populations presents another challenge because of threats from invasive species [6] or changes in ecosystem management in orchid habitats, such as grasslands [7] and forests. In the eastern US, fire suppression in forests has had a major impact on the characteristics of plant communities [8]. Orchid populations are threatened by the increased abundance of native species, especially herbivores [9]
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