Augmentation of a Whibley Wattle population in South Australia by translocation

Summary

Whibley wattle (Acacia whibleyana), a Critically Endangered shrub restricted to two small, fragmented, juvenile-free populations totaling roughly 354 plants near Tumby Bay, South Australia, was the subject of an experimental translocation by the Botanic Gardens of Adelaide comparing seed versus transplanted-seedling propagules under weedy and weed-free conditions at the Salt-lake population site. Weeds proved devastating to seed-founded plots, where only 0.7% of sown seed initially survived compared to 10% in weed-free plots, and all weedy-plot seedlings died by the following summer; transplanted seedlings fared far better overall, with survival stabilizing at 42% after seven years regardless of weed presence, though weeds still significantly reduced their growth. A separate full translocation of 58 ten-month-old seedlings planted along a disused, weed-free but soil-compacted track in 1996 saw 43% die during the first summer from falling soil moisture, but survivors grew rapidly, first flowering in 1999, and stabilizing at 43% survival after ten years, a 25% increase in the wild Salt-lake population; seedling recruitment, however, has not yet been observed and may require a fire or other disturbance event. The project's early success prompted further community-supported translocations between 2003 and 2006 involving local school students, aimed at eventually connecting population fragments into a stable metapopulation. Major difficulties included pervasive weed competition, historic vehicle damage to the site before fencing in 1995, and genetic erosion risk in small roadside sub-populations. The project rates itself Successful, having demonstrated reliable establishment and reproduction even without confirmed natural recruitment.