CSIRO PUBLISHING www.publish.csiro.au/journals/ajb Australian Journal of Botany, 2007, 55, 390–399 Population-size effects on seeds and seedlings from fragmented eucalypt populations: implications for seed sourcing for ecological restoration Siegfried L. Krauss A,B,F , Luise Hermanutz C , Stephen D. Hopper B,D and David J. Coates E A Science Directorate, Botanic Garden and Parks Authority, Kings Park and Botanic Garden, Fraser Avenue, West Perth, WA 6005, Australia. B School of Plant Biology, University of Western Australia, Crawley, WA 6005, Australia. C Department of Biology, Memorial University, St John’s, NL, A1B 3X9, Canada. D Present address: Royal Botanic Gardens Kew, Richmond, Surrey, TW9, 3AB, UK. E Science Division, Department of Environment and Conservation, Locked Bag 104, Bentley Delivery Centre, WA 6983, Australia. F Corresponding author. Email: skrauss@bgpa.wa.gov.au Abstract. Ecological restoration of degraded habitats is a major conservation activity requiring the collection of large amounts of native seed. Seed production and the genetic quality of seed may be influenced by properties of the source population, such as population size and fragmentation, potentially having an impact on restoration goals. We assessed the population-size effects on seed production and seedling performance in two Western Australian wheatbelt eucalypts, Eucalyptus salmonophloia F.Muell. and E. salubris F.Muell. Both species were historically widespread and dominant, but, as a consequence of land-clearing for agriculture, now exist as small, highly fragmented populations throughout the western half of their range. Given their former importance in the landscape, these species will be critical in ecological restoration of the region. We assessed small (n = 6–12) and large (n > 200) remnant populations in a highly fragmented landscape and compared these to large unfragmented populations. Seed number per capsule was dependent on population size and fragmentation for E. salubris, but not for E. salmonophloia. Large, unfragmented populations of E. salubris produced more than twice the number of seeds per capsule (mean = 2.95) than small and/or fragmented populations. However, seed germination, seed weight, seedling survival and seedling vigour to 1 year were independent of population size or fragmentation in both species. Our results suggest that reduced population size and increased fragmentation can negatively affect pollen quantity and/or quality, thereby limiting seed production, although no fitness effects were observed post-seed maturation. We suggest that the relative absence of post-seed maturation fitness effects in these small fragmented populations are a consequence of (1) wide outcrossing resulting from long-distance dispersal of pollen by highly mobile birds among fragmented populations and/or (2) efficient pre- or post-zygotic selection against more homozygous zygotes within fruits so that only relatively outbred seeds mature. The consequences on seed collection for ecological restoration of reduced population size and increased fragmentation for these eucalypts may be fewer seeds for the same collecting effort, but no apparent fitness effects of mature seeds. However, caution should be exercised when harvesting seed from these smaller populations, as over-harvesting may have an impact on recruitment and hence long-term persistence. Introduction The ecological restoration of altered natural systems is a widespread and expanding activity, and one of the most expensive of all actions of biological conservation (Holl et al. 2003). The collection of seed is a critical component of ecological restoration. Two key seed-collection issues that have restoration and biodiversity conservation repercussions are (1) provenance and (2) source-population effects on seed quality. Provenance addresses the issue of genetic similarity between seed source and sink populations, where poor genetic matching may have several potentially detrimental impacts for ecological restoration and biodiversity conservation (Hufford and Mazer 2003; McKay et al. 2005). Consequently, the delineation of local genetic provenance, and the identification of local-provenance seed-collection zones, has been a recent priority in ecological- restoration research (Krauss and Koch 2004; Carr 2005; Krauss et al. 2005a, 2005b; Bussell et al. 2006). However, the effect of population size and fragmentation on the quantity and quality of seed from seed-source populations is a second major issue that has attracted less research attention (Coates et al. 2005; Young 2005). Population size and isolation of the seed source can affect demographic and genetic properties in several ways. Reduced population size and increased isolation may disrupt interactions between plants and their pollinators, reducing plant reproductive success (Agren 1996; Young et al. 1996; Cunningham 2000). © CSIRO 2007 10.1071/BT06141 0067-1924/07/030390