Seed ecology informs restoration approaches for threatened species in water-limited environments: a case study on the short-range Banded Ironstone endemic Ricinocarpos brevis (Euphorbiaceae)

Abstract

Translocation of threatened species is challenging in semiarid environments, especially when seeds are the principal means of in situ establishment. Worldwide, the overall success of translocations using seeds is highly variable and generally unpredictable. Most seed-based translocations are embarked upon with limited understanding of the species’ seed biology or the nuances of the local abiotic environment in which to guide restoration approaches. For instance, within Australia just 14% of threatened species translocations use directly sown seeds and consequently, to improve the chances of restoration success, both the seed biology and the influence of the abiotic environment need to be adequately understood. We investigated these aspects in Ricinocarpos brevis R.J.F.Hend. & Mollemans – a short-range Banded Ironstone endemic – by focusing on a series of laboratory and field experiments to understand the key drivers of dormancy alleviation and germination promotion, as well as in-situ conditions of natural and recipient translocation sites. Fresh seeds were found to have high viability, fully developed linear embryos and possess physiological dormancy, with enhanced germination when exposed to smoke water, karrikinolide (KAR1) and gibberellic acid (GA3). Under laboratory conditions, seeds germinated over a range of temperatures (15−30°C), but germination was suppressed by light and highly sensitive to water stress. Seeds had reduced germination when sown on the soil surface, but could emerge from up to 13 cm in depth. Under field conditions, in-situ emergence was <2%. Using in-situ emergence results, soil loggers and rainfall data, we developed a model of the recruitment bottlenecks faced by this species under in-situ conditions, an approach that provides useful insights to assist future translocations. Understanding seed biology and seed ecology enables better insights into the principal bottlenecks restricting in-situ emergence and consequently restoration success, leading to the development of more effective approaches for conserving other threatened flora in future.