Assessing the Long-Term Viability of the Locally Restricted Species Calothamnus sp. Whicher and Hakea oldfieldii in a Threatened Ecological Community near Busselton Colin Yates, Margaret Byrne, Neil Gibson, Margaret Langley, Belinda Newman, Jane Sampson, Sean Stankowski and Rujiporn Thavornkanlapachai Science Division, Department of Environment and Conservation LMB 104 Bentley Delivery Centre Western Australia 6983 Final Report September 2009 Ecological and genetic investigations - Busselton ironstones 1 Executive summary Introduction The seasonally wet ironstone plant communities of the Swan and Scott Coastal Plains are amongst the most endangered in south-west Australia and are of national and international significance (Gibson et al . 2000). These plant communities, although historically restricted and rare, have been extensively cleared occurring in small isolated remnants and are now under considerable threat. For plant species in these fragments, populations are typically smaller and more isolated than they were historically, the abundances of their interacting species have changed, new species have been added, and the abiotic conditions and resources necessary for growth and reproduction have been altered. For sexually reproducing plant species, changes to the pollinator community and mate availability may have a number of important consequences for pollen flow, the mating system, seed production, and offspring fitness, factors which all influence population vital rates and viability (Hobbs & Yates 2003; Yates et al . 2007 ab). This report describes studies of the genetic and ecological factors affecting the viability of population fragments of two plant species, Calothamnus sp. Whicher and Hakea oldfieldii , in the Busselton ironstone community. Investigations of fruit set, seed production, seed fitness, the mating system, landscape level gene flow and demography were undertaken to determine how population size and connectivity influences the viability of plant population fragments for the two species. Key findings – Calothamnus sp. Whicher Flowering, fruit and seed production occurred in spring in each of the three years of the study. There were no significant differences in the proportion of flowers which set fruit or the number of seeds produced per fruit between years. Fruit set and the number of seeds per fruit varied between populations, but importantly there was no relationship with the number of plants in populations. Investigations of the mating system showed that seeds arise from a mixture of inbreeding and outbreeding. Levels of inbreeding were unusually high for a bird-pollinated shrub and are most likely consequence of geitonogamous self-pollination rather than biparental inbreeding (crossing between genetically similar plants). Rates of seed germination under controlled laboratory conditions varied between populations but there was no relationship with the number of plants in a population. The results for C. sp. Whicher contrast strongly with those of a similar study for the closely related but geographically widespread species Calothamnus quadrifidus. This species also has a mixed mating system, but progeny arising from self-pollination are aborted and as populations become smaller and mates fewer, the number of seed produced per fruit declines. Seed production in C. sp. Whicher is apparently robust to the effects of population fragmentation. Plants in small populations are able to go on producing substantial numbers of viable seeds despite the availability of mates declining. Ecological and genetic investigations - Busselton ironstones 2 Although similar levels of seed production occurred among different sized C. sp. Whicher population fragments, seedlings and juveniles were only observed in the medium- and large-sized population fragments. Seedling emergence was observed in each of the three years of the study but was highest in the wettest year of the study when rainfall was above average. Seedlings emerged in greatest numbers in areas of bare ground where vegetation cover was lowest. These conditions were not present in the smallest populations where annual weeds were abundant. Seedling mortality is high, but seedlings which survive are recruited into the juvenile population of plants creating populations with mixed-age structures. Medium and large-sized populations are currently stable or increasing in size, but small populations, because of a lack of recruitment, will decline and eventually be lost from the landscape. Genetic diversity in medium and large populations was higher than in small populations and was highest in the medium and large-sized populations. Genetic distances among populations are very high. A significant outcome of this is that all population fragments of C. sp. Whicher contain irreplaceable genetic diversity. Because of the high genetic differentiation between populations the loss of small populations will result in the significant loss of genetic diversity. Recommendation 1: Manage weed loads in the small populations to maximize the potential for recruitment. Recommendation 2: Conserve genetic resources of small populations by establishing ex situ collections and using seeds to rehabilitate suitable areas in or adjacent to medium or large populations. Recommendation 3: Conserve genetic resources of all populations through ex situ collections. Recommendation 4: Utilize seeds from all populations for replanting and restoration. Key findings - Hakea oldfieldii Flowering, fruit and seed production occurred in each of the three years of the study, but were significantly higher in the wettest year of the study when rainfall was above average. Fruit set and the number of viable seeds produced per weight of plant canopy varied between populations, but there was no clear relationship with population size, with the exception of the smallest population which produced significantly fewer seeds than other populations. Fruit were generally held on plants for no longer than two consecutive flowering seasons. Seasonal variation in seed production may make populations susceptible to local extinction following fire. Investigations of seed production and population fragment size were limited by the availability of populations. However investigations of the mating system showed that seeds arise predominantly from outbreeding due to a self-incompatibility system preventing effective self-pollination. As a Ecological and genetic investigations - Busselton ironstones 3 consequence small populations of H. oldfieldii will be susceptible to mate limitation and subsequent reductions in seed production . Seedling emergence was observed in one population in the wettest year 2007 when rainfall was above average. The low rates of seedling emergence and predominance of plants in adult size classes indicate recruitment may be more intermittent in H. oldfieldii than in C. sp. Whicher. Medium and large-sized populations may be relatively stable in the short term but patterns of recruitment suggest that populations will decline in the longer term. Genetic diversity in H. oldfieldii was moderate and similar among populations. Like C. sp. Whicher genetic distances among populations of H. oldfieldii are very high and all population fragments contain irreplaceable genetic diversity. Because of the high genetic differentiation between populations the loss of populations will result in the significant loss of genetic diversity. Recommendation 5: Manage weed loads in the small populations to maximize potential for recruitment. Recommendation 6: Conserve genetic resources of small populations by establishing ex situ collections and using seeds to rehabilitate suitable areas in or adjacent to medium or large populations. Recommendation 7: Conserve genetic resources of all populations through ex situ collections. Recommendation 8: Utilize seeds from all populations for replanting and restoration. Recommendation 9: Confirm that sufficient quantities of canopy stored seed are available in populations before controlled burning is undertaken. Ecological and genetic investigations - Busselton ironstones 4 1.0. INTRODUCTION The ironstone formations of the southern Swan Coastal Plain occur on massive ferricrete deposits that have formed at the foot-slopes of the Whicher Scarp over the last two million years. Skeletal soils overlying the massive ironstone become seasonally inundated and waterlogged in winter and dry out over summer. The ironstone environments support species rich shrublands containing a suite of restricted and endemic plant taxa and forming a unique plant community (Busselton ironstones, community type 10b; Gibson et al . 1994; Gibson et al . 2000; Meissner & English, 2005). The Busselton ironstone vegetation community contains a total of 15 endemic species, 11 Declared Rare Flora and six Priority species (Gibson et al ., 2000; Meissner & English, 2005) as well as a number of endemic ‘forms’ of more widespread species which are yet to have their taxonomic status resolved (Keighery 2004). This ironstone community is under considerable threat and is restricted to small isolated remnants due to extensive clearing for agricultural activities. It is estimated that 97% of the Busselton ironstone community has been cleared for agriculture, with approximately 68ha of native vegetation remaining (Gibson et al . 2000). These areas are highly fragmented, and restricted to roadside verges, rail reserves and small bushland remnants. Connectivity between these fragments is generally poor as the remnants are scattered