Floristics, dominance and diversity within the threatened Themeda grassy headlands of the North Coast Bioregion of New South Wales

Abstract

We surveyed subtropical closed tussock grasslands on headlands within the North Coast Bioregion of New South Wales. The aims of the investigation were to provide baseline data on this listed threatened community. Additionally, we tested the effects of macropod grazing and biomass changes on assemblages. In total, 117 full floristic survey plots were placed within extant natural grassland occurrences on 16 headlands. Data collected included the percentage cover and frequency of each species. In addition, we ranked the three species contributing most to overall biomass. Analysis of the full floristic cover data (percentage cover) was performed using the Kulzynski association measure and Unweighted Pair Group Arithmetic Averaging fusion strategy. Further analysis was performed using constrained and unconstrained ordinations and Generalised Additive Modelling using species frequency data and explanatory variables including overall, and proportional species biomass, and macropod grazing impact. Seven distinct grassland assemblages were derived, of which three were Themeda dominated. Concentrating on the Themeda-dominated assemblages, it was found that increasing biomass depth and a reduction in macropod grazing impact were associated with a reduction in plot species richness and diversity and trait richness and diversity. These changes were associated with a shift in floristic assemblage identity. All three Themeda assemblages are likely to provide a unique combination of functional resources and all should be maintained in order to promote landscape diversity. We predict that use of frequent fire is likely to cause homogenisation (reduced landscape richness) and loss of important components including listed threatened taxa.

Application of Risk-Based, Adaptive Pathways to Climate Adaptation Planning for Public Conservation Areas in NSW, Australia

“…RBM that focuses on management of local or regional drivers of change represents a business-as-usual approach to biodiversity conservation, through the reduction of threats to iconic species or communities (e.g., [40]), to enhance resilience to broader scale changes in climate [41,42]. However, the effectiveness of such approaches has been questioned [43,44], and this is reflected in our pathways as a shift away from management of in situ threats to a wider landscape-scale view of protected area management as risk levels rise.…”

The complex nature of headland shrub encroachment: The case of Headland Zieria (Zieria prostrata)

“…Field observations backed by the correlative analysis provided here indicate Headland Zieria may have a unimodal response to shrub occurrence. The species increases in dominance at the encroachment front or around isolated taller shrub patches (facilitative) and decreases in dominance in more open grass dominated areas (possible competition with Themeda, Hunter & Hunter ) but also is absent from deep within the Coastal Wattle and Coast Banksia shrub zone (potential competition with taller shrubs). Headland Zieria on the Banksia shrubland margins or underneath isolated patches of taller shrubs increased in height significantly (pers.…”

“…Plots measuring 2 × 2 m were placed randomly with a minimum distance of 10 m between sites across two strata; zones with known Headland Zieria populations and those without. Survey plots included 35 surveyed by Hunter and Hunter () and monitored between November 2015 and February 2016 and an additional 36 in October 2016 placed within Themeda grassland and additional plots within adjoining Banksia shrubland.…”

“…integrifolia; Morris et al 1990;Griffith 1992b;Dexter 2015;Dexter et al 2015). Very little has been published on the dynamics of these endangered Themeda grasslands with only limited correlative 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 mechanically or by the introduction of frequent fire (every 3-6 years) to protect and enhance both the Themeda grassland and Headland Zieria populations.…”

“…The prevailing concerns about shrub encroachment occur within the void of limited information; however, current management prescriptions include the removal of overstorey shrubs mechanically 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 dominated by prostrate shrubs such as Headland Zieria (Hunter & Hunter ).…”