Spatial patterns of presence, abundance, and richness of invasive woody plants in relation to urbanization in a tropical island setting

Tropical Pacific island countries, many of which are less-developed, are experiencing invasions of alien plant species at rates faster than areas of comparable size elsewhere. In this paper we examine the relationship between the presence, abundance, and richness of 14 invasive woody plant (IWP) species and level of urbanization and road type in the Greater Suva Urban Area (GSUA), Fiji. One hundred and fifty-four sample locations within a 29 km transect traversing urban, peri-urban and rural land sectors on local, collector and arterial roads were surveyed. We analyzed the 14 species for frequency of occurrence across the urban-rural gradient and found spatial patterns of IWP presence differed by species. We analyzed the abundance of seven species using multi-variable regression and found abundance was more often influenced by urban-rural sector than road type, though road type had a significant effect for some species. We conclude by offering plausible explanations for differences attributed to modes of dispersal, introduction history and human activities. We include supplementary material providing detailed characterization of biology, ecology, and history of the 14 target species. These findings are expected to help inform risk assessments and management of IWP in other tropical urban-rural gradients, and especially small island developing states.