Patterns of distribution, abundance and composition of forest terrestrial orchids

Abstract

Many terrestrial orchid species are known to grow in forest ecosystems, but the patterns of their diversity and habitat specialization have not been sufficiently explored. Niche parameters and factors influencing the distribution, abundance and composition of forest orchids in the central Balkans were investigated in the present study. Outlying mean index (OMI) analysis was used to explore ecological niches of orchids and environmental factors affecting the patterns of their distribution. Indicator species analysis was performed to identify species presenting strong affinity for specific forest and bedrock types. In addition, similarity profile analysis was applied to classify orchid taxa into meaningful groups, whereas the multi-response permutation procedure was used to analyse differences of orchid composition between forest types. Out of a total of 40 orchid species and subspecies analysed, 29 showed significant niche marginality. The first three axes of the OMI analysis explained 68.13% of total variability. Light, temperature, moisture, nitrogen and altitude were found to be the factors most effectively influencing the distribution and abundance of orchids. Seven orchids had statistically significant strong affinity for specific forest types, whereas eight orchids were statistically significantly correlated with specific bedrock types. Overall, six ecological groups of orchids were distinguished. The results suggest that specialist orchids occur at the extreme ends of the light, temperature, soil pH, moisture and altitude gradients. Moreover, most specialist orchid species were found from low to middle elevations. The results provide a useful basis for the successful design of strategies for the conservation of forest orchids.