Reinforcement of a population of chalky wattle on Eyre Peninsula, South Australia

Summary

Chalky wattle (Acacia cretacea), Critically Endangered and confined to a roughly 5-square-kilometre range on South Australia's Eyre Peninsula, faces threats from its tiny area of occupancy and grazing of seedlings by rabbits, kangaroos and stock, with no populations protected in a conservation reserve. The South Australian Seed Conservation Centre ran translocation trials over nearly a decade to test how to reinforce declining populations. An initial 1992 planting of 36 seedlings, half fenced, coincided with the region's highest rainfall in over 120 years and achieved strong results: after seven years, fenced plants averaged 2.8 metres tall with 85% survival and had flowered and fruited, while unfenced plants reached only 36% survival, mostly lost to grazing in their first two years. Later trials under typical dry conditions fared far worse: a 1996 planting lost 60% of seedlings to drought and a further 30-35% to grazing regardless of fencing, while a 1997 trial found hydrogel water-storage crystals in planting holes dramatically improved survival, with treated seedlings reaching over 70% survival in fenced enclosures within six months versus near-total mortality in untreated controls. Direct seed sowing performed poorly, with germination confined to a single shaded, moister microsite and all seedlings dead by year three, and nearly 400 further seedlings planted between 1998 and 2000 all died within four years. The project rates itself a failure overall, attributing its one clear success to an exceptionally wet planting year and identifying insufficient soil moisture and grazing pressure as the recurring causes of failure elsewhere, while flagging hydrogel treatment and fencing as promising tools for future attempts.