**4. Discussion**

### *4.1. Value of a Range of Diversity Metrics*

Phylogenetic and species composition metrics from this study have provided deeper insight into the diversity and composition of the Sunshine Coast heathlands than species richness alone. This has resulted in a more nuanced characterization of community distinctiveness and ongoing ecological processes [84]. In this study, no regional ecosystem on the Sunshine Coast was significantly different in terms of species richness, family richness, genus richness, or phylogenetic diversity. It was expected from earlier studies in heath over south-eastern Australia that the wetter alluvial regional ecosystems of heath would be significantly lower in species richness than the drier heath regional ecosystems [37,85,86], raising the contention that these wetter systems are not a priority for conservation. However, in some coastal heath regions of New South Wales, no species richness differences were found between wet and dry heaths but, as was found in this study, compositional differences were apparent [87]. So, what do the compositional and phylogenetic data from this study suggest?

### *4.2. Data Consistent with Theory of Evolutionary History of Heath Flora*

The phylogenetic tree from this study, and the lack of unique orders within the heath, is consistent with the theory that sclerophyll and heath vegetation evolved in the low nutrient and/or waterlogged areas within the extensive Australian Mesozoic rainforest [37]. Phylogenetic data in other studies, as well as the fossil record, have provided support for rainforest being the ancestral state of Australian flora, with the sclerophyllous component becoming more common after the Oligocene, with increasing climatic variability, seasonality, and aridity [38,88,89]. This resulted in the radiation of sclerophyll flora, including the Myrtaceae, Proteaceace, Ericaceae, and Casuarinaceae [90,91], all typical components of the heath flora. The overall phylogenetic diversity of the heath is considerably lower than

found in studies of corresponding rainforest areas [16,17,41]. All the heath ecosystems, except one, had a low phylogenetic diversity, ye<sup>t</sup> they also contained ancient lineages such as Proteaceae and Restionaceae. These data support the possible impact of deep-past processes on the phylogenetic patterns seen in the heath; it may not only be a result of present-day assembly processes, such as environmental filtering [26]. The NTI for each regional ecosystem showed a stronger (higher) clustering than the NRI, which has been suggested as indicating more recent diversification events [92], further supporting recent speciation in the heath. This has implications in terms of conservation, as maximizing phylogenetic diversity alone, without historical interpretation, can have negative outcomes [27].
