Irene Martín-Forés, Samantha L. Bywaters, Ben Sparrow, Greg Guerin

Orchids are potentially useful as ecological indicators because of their sensitivity to habitat fragmentation and anthropogenic disturbance. While many studies explore the effect of single factors on orchid diversity, few investigate how the extent, configuration and condition of surrounding habitat affect whole orchid communities. Here, we unravel the effect of biological invasions, anthropogenic disturbance (i.e. grazing pressure, ecological condition), habitat fragmentation and climate on an Australian orchid community. We sampled 39 plots across nine sites in the Mount Lofty Ranges, Australia. We recorded the number of orchid species and number of individuals per species in mid-winter, early-spring and late-spring to account for the effect of season on species visibility, with 115 surveys in total. We ranked grazing intensity and ecological condition, and estimated cover of exotic species. We analysed the response of richness and diversity through generalised linear mixed models, and differences in species composition through non-metric multidimensional scaling. Habitat configuration in the surrounding landscape had different effects at increasing radii, explaining 24–73% of variance. Patch-level orchid diversity was positively correlated with habitat edges in the immediate area, and with habitat cohesion at medium scales, whereas diversity was negatively correlated with increasing habitat area across larger surrounding areas. Orchids co-existed with exotic species but were negatively affected once exotic cover exceeded 20%. Species composition was correlated with exotic cover. Our findings reveal a complex relationship between orchid communities and their surrounding environments suggesting that while orchids benefit from a somewhat disturbed landscape, they fail to thrive once exotic cover exceeds 20%. These idiosyncratic responses suggest orchid diversity may be unreliable as early-warning indicators of habitat disturbance.