The complex nature of headland shrub encroachment: The case of Headland Zieria (Zieria prostrata) By John Thomas Hunter and Vanessa Hewlett Hunter John Hunter is an adjunct Associate Professor with the School of Environmental and Rural Science, University of New England (Armidale, NSW 2351, Australia. Tel +61 2 6775 2452; Email: jhunter8@bigpond.com. Vanessa Hunter is a senior ecologist within Hewlett-Hunter Pty Ltd, Armi- dale, NSW 2350, Email: vhhunter@bigppond.com. Summary Headland Zieria (Zieria prostrata) is an endangered species restricted to four headlands with a potential population of 1000 individuals. The species also occurs within the endangered ecological community Themeda grassland on sea cliffs and coastal headlands in the New South Wales North Coast, Sydney Basin and South East Corner Bioregions. Shrub encroachment of native species is perceived as a threatening process within these grasslands, and also to the unique species within them, such as Headland Zieria. Suggested management actions for the community and Headland Zieria include the removal of other shrubs by frequent fire or mechanical means. We conducted a survey and correlative analyses to test the validity of these proposed actions. We provide evidence that Headland Zieria is facilitated by a higher density of nearby shrubs which may provide protection from the elements and decrease competition from other understorey species but is eventually out competed by them when the grassland fully transitions to a Banksia shrubland. We suggest that Headland Zieria is an ecotonal specialist that may require an invasion front of shrubs and/or isolated patches. The implementation of fire and/or over- storey shrub removal may be detrimental where populations of Headland Zieria occur. Our study highlights the need to look more closely at interactions before management actions changing vegetation structure and composition are implemented. Key words: coast, fire management, Generalised Additive Modelling, monitoring, rutaceae, threatened species. Introduction H eadland Zieria (Zieria prostrata J.A.Armstrong) is described as a com- ponent of the endangered ecological com- munity, Themeda grassland on sea cliffs and coastal headlands in the New South Wales North Coast, Sydney Basic and South East Corner Bioregions, under the NSW TSC Act. It is suggested these com- munities are in decline due to the absence of fire encouraging shrub encroachment, particularly by Coastal Wattle (Acacia longifolia var. sophorae (Labill.)) Court and Coast Banksia (Banksia integrifolia L.f. subsp. integrifolia; Morris et al. 1990; Griffith 1992b; Dexter 2015; Dexter et al. 2015). Very little has been published on the dynamics of these endangered The- meda grasslands with only limited correla- tive research conducted very recently (Dexter 2015; Hunter & Hunter 2017). The prevailing concerns about shrub encroachment occur within the void of limited information; however, current management prescriptions include the removal of overstorey shrubs mechani- cally or by the introduction of frequent fire (every 3–6 years) to protect and enhance both the Themeda grassland and Headland Zieria populations. The endangered community as it occurs in northern New South Wales is a mosaic of small grassland areas within a matrix dom- inated by prostrate shrubs such as Head- land Zieria (Hunter & Hunter 2017). Headland Zieria (Zieria prostrata) was first discovered in 1981 and formally described by Armstrong (2002). While additional prostrate forms of the closely related Sandfly Zieria (Zieria smithii Jacks) were found soon after its descrip- tion, Hogbin and Crisp (2003) provided evidence to confirm the erection of the taxon to specific status using morphomet- ric analysis and genetic data. Headland Zieria was originally known from three headlands (Look At Me Now, Damerells and Bare Bluff) along a three kilometre stretch of coastline north of Coffs Harbour (Hogbin & Peakall 2000). Griffith (1992a) estimated the total population to be in the order of 400 individuals and found a fourth population on Diggers Point. The species was also presumed to have occurred further south on Bonville Head- land. Genetic investigations and inter- views conducted by Hogbin and Peakall (1999) suggested that the Bonville Head- land population was a misnomer and the collections were probably a mislabelling of material from Diggers Point. Research into the reproductive biology of Headland Zieria revealed sufficient pollen produc- tion, good seed set and germination with shallow seed burial and soil disturbance enhancing recruitment (Hogbin & Peakall 2000). Further surveying increased the population estimate to over 1000 individu- als (Hogbin & Peakall 2000). Currently, Headland Zieria is listed on the Federal Environmental Protection and Biodiver- sity Conservation (EPBC) Act and the State Threatened Species Conservation (TSC) Act as endangered. ECOLOGICAL MANAGEMENT & RESTORATION VOL 18 NO 2 MAY 2017 115 ª 2017 Ecological Society of Australia and John Wiley & Sons Australia, Ltd doi: 10.1111/emr.12255 COMMENT PIECE Ecological Society of Australia