Identification of distinctive new rainforest communities in the Greater Blue Mountains World Heritage Area, Australia

Abstract

Aims : When vegetation mapping does not match well to vegetation on the ground, it becomes difficult to manage and regulate appropriately. Here, we conducted field validation of regulatory vegetation map units known as Plant Community Types (PCTs) in the Greater Blue Mountains World Heritage Area (GBMWHA) assessing the potential extent of PCT misclassification, and generating new mapping and descriptions of rainforest communities. Location : Greater Sydney, Australia. Methods : We estimated cover-abundance for vascular species and presence of bryophytes species at 55 plots. We compared field data to that of locally mapped and other regional PCTs using ordination, PERMANOVA and government-developed tools for end users. We assessed the utility of bryophytes, which are typically overlooked in vegetation classification, for delineating between vegetation types. High-resolution spatial data and ground truthing were used to map the putative extent of rainforest in the study area. Results : We identified clear mismatches between local floristic composition and mapped PCTs. Vegetation at our field sites comprised two distinctive communities and did not correspond well to any locally defined PCT or other regional PCTs. Bryophyte assemblages also differed between our two surveyed communities. 65% of sites surveyed were in areas mapped as sclerophyll-dominated forest but had floristic assemblages consistent with rainforest. More broadly, >90% of putative rainforest identified by our mapping approach is mapped as sclerophyll forest under PCT mapping, with rainforest extent likely three to four times greater than PCT mapping indicates. Conclusions : We propose two new vegetation types in the GBMWHA and recommend these be included in revisions to the PCT classification: ‘Hawkesbury Warm Sheltered Gully Rainforest’ and ‘Hawkesbury Subtropical-Dry Bench Rainforest’. Fires and pressures from urban development will likely threaten the integrity of these rainforests in future. Revision of PCT mapping and measures aimed at mitigating threats to remaining patches is urgently required to protect the Outstanding Universal Values of the World Heritage Area. Taxonomic reference : Australian Plant Census, IBIS database (http://www.chah.gov.au/apc/index.html) [accessed 27 Jan 2026]. Abbreviations : GBMWHA = Greater Blue Mountains World Heritage Area; HK = Hawkesbury; NSW = New South Wales; PCT = Plant Community Type; SVTM = State Vegetation Type Map.