Assessing the incursion status of non-native plant species in the Wet Tropics World Heritage Area in Queensland, Australia

Globally, invasive species, climate change and increasing tourism are currently recognised as the three most significant threats to Outstanding Universal Values of natural World Heritage listed Areas. This study investigated the threat of incursion of invasive plant species associated with access roads in the Wet Tropics World Heritage Area in Queensland, Australia. We assessed species richness, abundance, and the spread of non-native plant species along roads and in the adjacent vegetation using 306 1m2 quadrats along 34 transects first sampled in 2015 and resampled in 2021. Plant species and vegetation cover of all ground-layer plants were recorded. Thirty-one non-native plant species were recorded, and their richness was found to be significantly higher at the road edge (27 species) than in the adjacent vegetation (16 species). Non-native plant species richness and cover decreased with distance from the road edge, in contrast to that of native plants which showed an increase. Many significant associations were detected including those between non-native plant cover, non-native species richness, native plant cover, plant litter cover, forest canopy cover, bare ground, rock and stones cover, and time since last fire (P < 0.05). Vegetation cover for more than 73% of the recorded non-native species at the road edge was < 5%. The large number of non-native species and the potential for a small set of these species to dominate the road edge and spread into the adjoining environment, highlights the need to mitigate the impacts of linear infrastructure development in protected areas, and the importance of timely surveillance and targeted control of non-native plants at road edges to avoid their spread into the adjacent vegetation.