A plot-based analysis of the vegetation of the Northern Territory, Australia: a first assessment within the International Vegetation Classification framework

Aims: To develop an interim classification of the vegetation of the Northern Territory at the International Vegetation Classification (IVC) division (level 4) and macrogroup (level 5) levels. These types are produced to assist in the development of an integrated nationwide plot and floristically based classification of Australia allowing integration within a global perspective. Study Area: The Northern Territory of Australia covers an area of 1.42 million square kilometres, almost 20% of Australia's land mass. It comprises three distinct climatic zones including tropical, subtropical and arid vegetation types. Methods: We used collated vegetation data held by two organisations: the Northern Territory Government, Department of Environment, Parks and Water Security and the Terrestrial Ecosystem Research Network (a total of 45,710 plots used). We applied semi-supervised quantitative classification methods to define vegetation types at the IVC division and macrogroup levels. Analyses used kR-CLUSTER methods on presence/absence data. Macrogroups were characterised by taxa with the highest frequency of occurrence across plots. Additional analyses were conducted (cluster) to elucidate interrelationships between macrogroups and to assist in the assessment of division level typology. Results: We propose 21 macrogroups and place these within higher thematic levels of the IVC. Conclusions: We found that the IVC hierarchy and associated standard procedures and protocols provide a useful classification tool for Australian ecosystems. The divisions and macrogroups provide a valid framework for subsequent analysis of Northern Territory vegetation types at the detailed levels of the IVC. A consistent typology for the Northern Territory (and hopefully in future, for all of Australia) has numerous benefits, in that they can be used for various applications using a well-structured, systematic and authoritative description and classification that is placed in a continental and global context, readily enabling the one system to be used in studies from the local to global level. Taxonomic reference: Northern Territory Herbarium (2022). Abbreviations: DVT = Definitive Vegetation Type; IVC = International Vegetation Classification; nMDS = non-metric multidimensional scaling; NT = Northern Territory; NTVSD = Northern Territory Vegetation Site Database; NVIS = National Vegetation Information System; WA = Western Australia