Naturalised plants transform the composition and function of the New Zealand flora

Abstract

The New Zealand flora has a high proportion of endemic species but has been invaded by almost the same number of non-native plant species. To support management of invasive plant species, we provide an updated inventory of New Zealand’s naturalised flora and compare it with the native flora to identify key taxonomic and functional distinctions. We also assess how the naturalised flora may impact ecosystem processes differently than the native flora using functional traits related to plant resource use strategy. The 1798 species in the naturalised flora currently comprise 43.9% of the total number of vascular plant species, and add 67 plant families and 649 genera to the total vascular flora. The naturalised flora has a greater proportion of herbaceous species and annual species than the native flora, which could influence ecosystem processes such as decomposition and nutrient cycling. Naturalised trees have higher leaf nitrogen concentration for a given leaf area than native trees, which could increase rates of nutrient cycling in invaded forest ecosystems. A greater number of naturalised species are present in larger, more northerly, and more populated regions of New Zealand. Our results demonstrate both taxonomic and functional differences between the native and naturalised flora of New Zealand that can be used to guide management of naturalised plants, including the 314 species currently managed as environmental weeds, from the local to national scale.