Wind Dispersal of the Vagant Lichen Chondropsis semiviridis in Semi-arid Eastern Australia

Abstract

A field-based wind tunnel was used to assess threshold wind velocities required to initiate movement of the vagant lichen Chondropsis semiviridis (F.Muell. ex Nyl.) Nyl. in a semi-arid eastern Australian woodland. Threshold wind velocities were lowest on bare surfaces (21 km h^-1) and highest on surfaces covered with the needle-like litter of Casuarina cristata Miq. 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 time in summer. The extensive litter cover in the groves, and the tendency of C. semiviridis to firmly attach to this litter, probably explains the concentration of C. semiviridis in the groves and the low rates of migration and emigration during most years. It is hypothesised that migration of C. semiviridis between timbered groves would only occur during extreme droughts when pasture and litter cover are sparse.