IMPORTANCE OF WOODY DEBRIS IN SEED-GERMINATION OF TIPULARIA-DISCOLOR (ORCHIDACEAE)

Concerns about declining populations of terrestrial orchids make it im portant to identify the environmental factors crucial to seedling recr uitment. This study shows that.seedlings of Tipularia discolor (cranef ly orchid) primarily occur on decomposing wood. Extensive searches of decomposing logs and stumps in mature and successional forests reveale d seedlings at 24 sites, of which 15 could be identified as originatin g from seven different deciduous trees and one conifer. Seeds were pla nted in natural habitats to test the hypothesis that germination requi res decomposing wood. In one experiment, seeds were placed into soil a t sites where adult plants were abundant; no germination resulted. In a second experiment, germination of seeds sown in ambient soil was com pared with sowings in plots amended with decomposing wood collected fr om a stump where spontaneous seedlings grew. Germination was much more frequent in plots amended with decomposing wood. We conclude that ger mination of T. discolor is stimulated in substrates that contain decom posing wood; judging from the occurrence of spontaneous seedlings, woo d from at variety of tree species offer a suitable substrate.