Recognising the Fourth Nature: A Case Study of Spontaneous Urban Vegetation in Southwest Australian Cities

Urban nature exists in all cities, including spontaneous nature. Spontaneous vegetation has been well-documented in the broader ecological literature in the Northern Hemisphere in recent decades. However, the recognition of, and interest in, spontaneous nature in Australia is limited. Our study initiated research on spontaneous vegetation in Southwest Australia from a landscape architectural site analysis approach with vegetation surveys. This study created an inventory of plants in four biotope types (specific abiotic environments with associated plant communities), i.e., cracks, walls, margins, and vacant lots, in two cities. Twenty-four sites were surveyed four times over a calendar year, and 145 plant species were identified. More than 90% of the species were naturalised, with native ranges most common in the Mediterranean Basin (34 species), and predominantly annuals (73 species). Only eight species were native to Southwest Australia. Our analysis revealed some of the cultural and ecological characteristics of these sites and species, i.e., environmental histories, pollinator habitats, the temporary statuses of sites with spontaneous nature, and their potential, e.g., altering maintenance schedules to retain foraging resources. Therefore, this study recommends further exploration of spontaneous nature through small-scale site analysis approaches and at larger scales for a more detailed understanding of this, at present, overlooked part of nature in Southwest Australian cities.