The ecological relationships and demography of restricted ironstone endemic plant species: implications for conservation

We investigated the ecological relationships, reproductive biology and demography of four shrub taxa restricted to ironstone ranges in south-western Australia, to assess the feasibility of post-mining reintroductions. We found that three taxa were restricted to narrow fissures in massive ironstone and the fourth was restricted to fissures and skeletal soils over ironstone. In all taxa, adult plants were the most abundant life stage in populations and produced seeds annually. Newly emerged seedlings were observed in low numbers each winter of three census years, with the highest rates occurring when winter rainfall was above average in the semiarid Mediterranean climate. Mortality was highest and most variable for <1-year-old seedlings (50–93%), 1-year-old seedlings (17–67%), juveniles (21–54%) and vegetative adults (6–50%), and was lowest and least variable for the reproductive adults (2–7%). The restriction of three of our study taxa to narrow fissures excludes the option of using seedlings in reintroductions. Using seeds, although possible, will be both an inefficient and a high-risk strategy for at least three of the four taxa studied. This is because of the low frequency of years when winter rainfall is sufficient to stimulate high rates of seed germination, coupled with the consistently high rates of seedling mortality in most years, and no easy method for determining which rock fissures will be suitable for plant establishment. The more widespread taxa showed reproductive and demographic characteristics similar to those of the taxa restricted to the narrow fissures, indicating that establishment of many species will be difficult in this environment.