Using hierarchies of cause to inform conservation of a naturally rare but critically endangered shrub Lasiopetalum pterocarpum (Malvaceae s.l.)
C. F. Wilkins A , P. G. Ladd B D , B. J. Vincent C , A. D. Crawford C and L. W. Sage CA School of Plant Biology, The University of Western Australia, Crawley, WA 6009, Australia.
B School of Environmental Science, Murdoch University, Murdoch, WA 6150, Australia.
C Department of Environment and Conservation, Bentley, WA 6983, Australia.
D Corresponding author. Email: P.Ladd@murdoch.edu.au
Australian Journal of Botany 57(5) 414-424 https://doi.org/10.1071/BT09040
Submitted: 20 February 2009 Accepted: 16 June 2009 Published: 14 September 2009
Abstract
Understanding the causes of rarity and ways of managing populations of rare species is essential for their successful conservation. The present study applies the conceptual model of a hierarchy of causes to Lasiopetalum pterocarpum E.M.Benn. & K.Shep. (a critically endangered species) to understand better its reproductive and ecological attributes, possible reasons for its rarity and to determine whether this model assists in developing management strategies. L. pterocarpum subpopulations from Serpentine National Park were censused to record abundance, plant health, phenology, flower and fruit production and the presence of any seed bank. These characteristics were matched to criteria in the hierarchies of cause model. There was no evidence of recent seedling recruitment at any subpopulation. Hand-pollination produced a flower-to-fruit conversion proportion similar to that found in the field and self- and cross-pollinations produced virtually the same fruit set. Seed store in soil from beneath the native subpopulations and at a translocation site showed seed was patchily distributed and infrequent. L. pterocarpum is an obligate seeder, killed by fire and dependent on disturbance to break seed dormancy. However, smoke has no effect on germination. Seed production does not constrain population growth, because seedling regeneration after fire in 1999 was prolific at sites where plants had been growing. In the hierarchies of cause framework, the main causes of rarity for this species are taxon ecology, life-history strategy and stochasticity. Thus, concentrating active management on factors related to life history such as mosaic patch burning, fencing after fire to exclude vertebrate grazers, weed control and establishment of translocated populations will aid the preservation of this species in the wild.
Acknowledgements
Thanks go to the PERTH herbarium for access to specimens, Serpentine National Park rangers for advice and access, the Water Corporation of Western Australia for access at Serpentine Dam, Alan Wright for information about further locations of L. pterocarpum, and Wally Gibb and John Wilkins for field assistance. Gary Cass provided logistical support. The South West Catchment Council (Department of Environment and Conservation, Western Australia) provided Natural Heritage Trust funding to this project.
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