Temporal and spatial patterns of orchid species distribution in Greece: implications for conservation

Studies comparing species’ distribution range at different time periods provide valuable information about temporal trends, and may help to identify the factors responsible for these changes. This knowledge is vital for setting conservation priorities and applying suitable management strategies and practices focused on species’ conservation. We examined records produced before and after December 31, 1985 for determining possible changes in the distribution range of 195 orchid species recorded in Greece, using a 10 × 10 km grid as the recording unit. We used regression techniques to explore the association of species richness with environmental and spatial variables. Species richness was calculated by using the orchid records made (a) before December 31, 1985, (b) after January 1, 1986, and (c) in both time periods. Generalized linear models (GLM) were used for identifying the most significant factors associated with the distribution of the threatened orchids of Greece. Most Greek orchids showed an increasing trend in distribution from the first to the second period, with the exception of a few Critically Endangered species, whose distribution was larger in the first than in the second period. The spatial distribution of the threatened orchids was mostly explained by land area and the area of the calcareous substrates at each grid cell, whereas all variables that were used in the GLM analysis accounted for about 32% of the variance. The observed increasing trend in orchid distribution should be attributed to the extensive research efforts during the second period, especially in areas of high altitude and towards the northern parts of Greece. Our results did not support the findings of other studies, mainly from northern Europe, which showed a significant decline in the distribution range of their orchid flora. These differences in distribution trends could be attributed to the complex orographic configuration of Greece, which renders large parts of the country rather unsuitable for agricultural use or for extensive urban development.