The nomination of the Porongurup Range was initiated by the Australian Heritage Council. The comparative analysis includes criteria (a), (e), (h) and (i). No specific claims were made for Indigenous values against the criteria. However, Indigenous stories are associated with the place, and are considered below in criterion (i).
Criterion (a) The place has outstanding heritage value to the nation because of the place’s importance in the course, or pattern, of Australia’s natural or cultural history Much of the Earth's species diversity is concentrated into a few relatively small areas. Thirty-four regions have been internationally identified as ‘biodiversity hotspots’, which together cover only 1.4 per cent of the Earth's land surface but contain nearly half of all plant species and a third of all terrestrial vertebrate species. These ‘biodiversity hotspots’ are based on the richness of species and on the occurrence of endemic species per area. The south-west of Western Australia, which is renowned throughout Australia and internationally for its species diversity and endemism, is one of these regions, and to date the only one in Australia (Myers et al. 2000; Mittermeier et al. 2004). The region has an estimated 8,000 plant species, and of these, at least 75 per cent are endemic (Hopper 1992, Hopper et al. 1996).
The South-West Botanical Province is one of only five ‘hotspots’ with Mediterranean-type ecosystems in the world, and rivals the exceptional species diversity found in the Cape Floristic region of South Africa, the California Floristic province of North America, and the Mediterranean Basin of Europe. Of more than 5,570 vascular plant species found here, nearly 2,950 are endemic (about 53 per cent). Impressive plant endemism in south-west Australia is attributed to millions of years of isolation from the rest of Australia by the country's vast central deserts. Extreme climate shifts and poor soils have also promoted specialisation of the region's flora.
The south-west hot spot incorporates the Porongurup National Park, as well as a number of other national parks including the larger Stirling Range National Park which is listed in the National Heritage List under criterion (a), and is located immediately to the north, the Fitzgerald River National Park in the south-east of the region and the Lesueur National Park north of Perth (which are both under assessment for the National Heritage List).
Porongurup National Park constitutes a major centre of plant species richness, having one of the richest concentrations of plant species in Australia with more than 700 native plant species within the park of 2,621 hectares. This compares well with Stirling Range National Park, an area of 115,000 hectares which has about 1,500 plant species recorded. Stirling Range National Park is more than 43 times the size, with just over double the number of plant species, and is considered to be an important remnant, recognised for its richness and endemism of plant species (Comer et al. 2001, Hopper et al 1996). The only other areas in Australia apart from a few select sites in the south-west that have comparable species richness and endemics, include an area in the wet tropics near Cairns, and an area on the border between NSW and Queensland.
A great diversity of plant species occurs in the park, due to the topographic diversity and range of microhabitats. An analysis was done using the Australian Natural Heritage Assessment Tool (ANHAT). In this analysis, the Mount Barker mapsheet, which encompasses the boundary of the Porongurup National Park, falls within the top one per cent of all 1:100 000 mapsheets across Australia for species richness and endemism for a number of plant families and genera. As not all plant families can be analysed in ANHAT, and as the Porongurup National Park is considerably smaller than the Mt Barker mapsheet, the analysis was complemented by using a full plant species list for the park (Keighery 1999, ANHAT 2007). The Porongurup National Park is the largest reserve on the Mt Barker mapsheet.
The Mt Barker area ranks exceptionally high for both richness and endemism values of vascular plants in general (ANHAT 2008). It ranks fourth in the country for Streptobionta (vascular plant) richness, behind the Swan coastal plain and Perth area. It is also among the top nine mapsheets in the country for vascular plant richness and endemism, rivalling the area around Stirling Ranges and Albany, an area of the wet tropics adjacent to Cairns in Queensland, around the Swan coastal plain and Perth, and an area around Lesueur National Park to the north of Perth. Effectively, along with the Stirling Range and Albany area, it is in one of the four major nodes of plant richness and endemism in the country.
Porongurup National Park is important for its endemism and richness in a wide array of plant species including heaths (Epacridaceae) especially beard-heaths (Leucopogon); peas (Fabaceae) notably flame-peas (Chorizema) and also bitter-peas (Daviesia and Bossiaea), and poison-peas (Gastrolobium); native myrtles (Myrtaceae); pimeleas (Thymelaeaceae), notably rice flowers (Pimelea); sundews and pitcher plants (Nepenthales); bloodroots, conostyles, kangaroo paws and their allies (Haemodorales); and banksias and grevilleas (Proteales). It is also important for richness in lilies, orchids and allies (Liliales), notably native lilies (Anthericaceae), irises and allies (Iridaceae), orchids (Orchidaceae), and flax-lilies and allies (Phormiaceae) (ANHAT 2008, Keighery 1999).
Invertebrates: At various times the Porongurup Range has been isolated as a true island, most recently during the Eocene period (55 million years ago) when the sea reached as far as the Stirling Range (Olver 1998). The Porongurup Range has acted as a refuge to invertebrate species, and many of the species here are recognised as Gondwanan, such as species of spiders, insects and land snails, which are more closely related to groups in mountainous areas of eastern Australia, Tasmania, New Zealand and other Gondwanan continents, than to the surrounding lowlands in the region (Olver 1998). Species from wetter Gondwanan times have been able to survive here in part because the moist granite outcrops provide an ideal refuge environment.
The ANHAT analysis (2008) indicates that the Porongurup National Park is significant at a national scale (it is amongst the top 1 per cent of places around Australia) for endemism and richness in spiders, in particular primitive trapdoor spiders (Mygalomorphae), including trapdoor spiders (Idiopidae) brushless-legged trapdoor spiders (Migidae), two-doored trapdoor spiders (Actinopodidae), and funnel-web spiders (Nemesiidae). These have a Gondwanan distribution, for example genera of the Migidae family have a restricted distribution in Australia, but are also found in southern Africa, and are thought to be a relict of Jurassic times when Africa was joined to Australia 140 million years ago (Main 1993). As a further comparison, in a survey of spiders in mountainous areas of the south west of Western Australia (Barrett 1996), the Porongurup Range was found to have the greatest species richness and the greatest abundance of spiders, and rivals the Stirling Range National Park, which is also recognised for its diversity and endemism of spiders.
A further analysis (ANHAT 2008) shows that the Mount Barker mapsheet is one of the richest places in Australia for land snails, particularly for species within the Bulimulidae family, which represents one of the dominant land snail and slug families in Australia. The richness of land snails is significant not only in itself, but because land snails have been demonstrated as an indicator species of areas of moist refugia over long periods, in addition to being indicative for areas that are significant for narrow range endemic invertebrates. These land snails have strong Gondwanan affinities. However, there is not enough evidence to determine whether the land snail richness of the mapsheet is reflected within the boundary of the Porongurup National Park. For other fauna, the Porongurup National Park was not found to be more than of regional or state-level significance.
The Porongurup National Park is a place of exceptional biological and ecological significance. Very high endemism and richness for vascular plant species concentrated in a relatively small remnant area, and high richness and endemism of spiders make the Porongurup Range an outstanding site. On this basis the Porongurup National Park has outstanding heritage value to the nationunder criterion (a).