Distribution and population structure of the vulnerable riparian palm Livistona lanuginose A. N. Rodd (Arecaceae) in the Burdekin River catchment, north Queensland

Abstract

This study investigated the distribution and population structure of Livistona lanuginosa, a vulnerable palm that is mainly restricted to riparian areas in the Burdekin River catchment. The known population, though dispersed, is composed of small and isolated sub-populations which are located entirely on pastoral leases. Mapping of the occurrence of L. lanuginosa indicates that distribution is primarily linear in the riparian zone along first and second order streams, as well as associated flood zones. A total of 510 adult plants, recorded at the eight sites surveyed, suggests that the overall population size is limited. The population structures at four sites indicate a stable population at those sites, whilst the population structures at the other four sites indicate unstable and senescent populations. The greatest proportion of individuals is in the seedling stage, thus indicating that sufficient viable seed is being produced and that conditions for germination and the development of seedlings are favourable. However, prominent gaps in life stage classes at some sites suggest that recruitment is limited or is not taking place at those sites, and this situation is reflected in high numbers of intermediate life stage classes and adult palms compared to seedlings and lower life stage classes. Livistona lanuginosa remains largely unprotected from livestock and fire, and other exogenous disturbances throughout its limited range, and the small total population size makes it vulnerable to rapid decline given unfavourable natural conditions.