Habitat effects and differences in the reproductive success of Orchis punctulata and Orchis purpurea (Orchidaceae)

The pollination success of two nonrewarding orchids in two coarse habitats was examined. The comparative results of Orchis punctulata and O. purpurea showed a significant differentiation. The fruit set of O. purpurea was significantly greater compared to O. punctulata, whereas both species also had significantly higher fruit set in the grassland compared to the forest. Although the pollination success of O. purpurea was not significantly correlated with plant height, inflorescence size, or nearest neighbor distance, these factors were found to be significantly correlated to the pollination success of 0. punctulata. Among these factors, the nearest neighbor distance had the highest impact on the pollination success of O. punctulata, whereas the respective effects to the individuals of O. purpurea were found to be nonsignificant. The results demonstrate that the distribution of 0. punctulata at the edges of its range is not delimited by factors related to its pollination effectiveness and that other factors, mostly related to the microsite conditions, might play a more significant role in the colonization of more western areas. Moreover, suitable management treatments that would increase the light levels within the forest sites studied may also increase the pollination success and the fruit production of the studied orchids.