How accurate is SVTM Mapping on the NSW North Coast?

Reliable vegetation maps are crucial for managing fire frequencies for the conservation of biodiversity and bushfire risk. In New South Wales (NSW), recommended fire intervals vary by structural formation and include dry sclerophyll forests (DSF; fire every 7-30 years) and wet sclerophyll forests (WSF; 25-60 years). However, the recent NSW State Vegetation Type Map (SVTM) reclassifies extensive areas formerly mapped as DSF in regional maps, to WSF, effectively doubling the recommended interval between fires in these forests. To assess the validity of SVTM classification of sclerophyll forests, data from BioNet Survey Plots (5213) across the NSW north coast were compared to the diagnostic features of the NSW key to vegetation formations (tree height >30m, floristic indicators).

SVTM mapping of WSF was found to be highly inaccurate, with 80.8% of corresponding plots not meeting the diagnostic canopy height threshold for WSF (>30m) and 24.8% of plots meeting neither canopy height nor floristic indicator criteria for WSF. Floristic indicators of dry sclerophyll forest were also widespread among plots misclassified to WSF, including in the understorey (50% of plots) and canopy trees (42%). Most plots misclassified to WSF were long-unburnt at the time of survey (73%), likely increasing the cover-abundance of WSF indicators (‘soft-leaved shrubs’) at the expense of DSF ‘grasses’ and ‘hard-leaved shrubs’. Vital attribute analysis indicates that most taxa on misclassified sites are sensitive to infrequent fire – vulnerable to localised extinction (55%) or decline (3%) – highlighting potential consequences of extended fire intervals following misclassification.

Low-frequency fire is already a major threat to the region’s dry sclerophyll forests, causing widespread structural change and habitat decline. The widespread misclassification of dry- to wet-sclerophyll forests identified in this study and the subsequent lengthening of recommended fire intervals is likely to further promote ongoing fire exclusion and biodiversity decline in the region’s dry sclerophyll forests.

The findings of this study were presented Nature Conservation Council’s Bushfire Conference 2023.