Wind dispersal of the vagant lichen Chondropsis semiviridis in semi-arid eastern Australia

A field-based wind tunnel was used to assess threshold wind velocities requ ired to initiate movement of the vagant lichen Chondropsis semiviridis (F.M uell. ex Nyl.) Nyl. in a semi-arid eastern Australian woodland. Threshold w ind velocities were lowest on bare surfaces (21 km h(-1)) and highest on su rfaces covered with the needle-like litter of Casuarina cristata Mig. trees (58 km h(-1)). Examination of wind speed data suggests that threshold wind velocities for movement on litter-covered surfaces occur about 1% of the t ime in summer. The extensive litter cover in the groves, and the tendency o f C. semiviridis to firmly attach to this litter, probably explains the con centration of C. semiviridis in the groves and the low rates of migration a nd emigration during most years. It is hypothesised that migration of C. se miviridis between timbered groves would only occur during extreme droughts when pasture and litter cover are sparse.