Samantha Bywaters

and 2 more

Wild orchids are threatened due to a range of demographic pressures, most important of which is herbivory. Exclusion fencing is commonly used to protect orchid populations from over grazing by pest animals, but the long-term demographic impacts and effectiveness of such interventions (for example vegetation competition and exclusion) have been poorly studied. The aim of this study is to assess the use of exclusion fencing as a conservation tool by measuring orchid abundance and diversity within fenced vs unfenced plots. Orchids were surveyed at twenty plots across five sites during spring 2020 with additional data including grazing intensity, ecological condition and percentage of weed cover ranked at each plot. Using generalised linear mixed models, non-metric multidimensional scaling and correlation analysis, orchid species abundance was found to be significantly higher (65% higher) in fenced vs unfenced plots. Orchid species diversity was highest in plots that had been fenced for the least amount of time or that had experienced a fire in the previous year. It was also found that sites that had been fenced for the longest period (42 years) were dominated by orchids capable of clonal reproduction. Results obtained indicate that whilst exclusion fencing offers immediate protection from herbivores, it leads to increased vegetation coverage within a plot which is associated with orchid species assemblages deferring to clonal rather than sexual reproduction. Such a reproductive strategy shift may lead to a “loss of sex” within local orchid communities, a known extinction pathway. To maintain natural orchid diversity within herbivore exclusion areas, requisite disturbance events such as slashing, strategic herbivore grazing and prescribed ecological burns should form part of a long term management strategy.