Planting conditions improve translocation success of the endangered terrestrial orchid Diuris fragrantissima (Orchidaceae)

Abstract

By conducting reintroductions of the endangered terrestrial orchid Diuris fragrantissima D.L.Jones & M.A.Clem. we compared planting at the following three stages of the natural perennial growth cycle: as actively growing symbiotic plants in spring and autumn and as dormant tubers in summer. Plants reintroduced in spring and autumn were incorporated into randomised treatments involving soil aeration and addition of a mycorrhizal fungus. The addition of a mycorrhizal fungus and soil aeration together significantly increased survival and flowering of plants reintroduced in spring, whereas they had no significant effect on plants reintroduced in autumn. Addition of a fungus without soil aeration did not improve plant survival or flowering. Reintroducing actively growing plants was more successful than reintroducing dormant tubers, with 32.5% and 29.1% plants (reintroduced in spring and autumn, respectively) and 11.0% of tubers persisting after 4 years. Although survival of reintroduced plants declined at a rate of 16.9% per year for 4 years following reintroduction, survival of remnant plants remained relatively constant, ranging from 80.0 to 93.0%. Tuber size was positively correlated with survival and flowering of reintroduced plants for 2 years following reintroduction. A general trend was observed towards the increased likelihood of re-emergence and flowering of plants that flowered in previous seasons.