Native woody plant recruitment in lowland forests invaded by non-native ground cover weeds and mammals

Globally, lowland forests have been depleted, fragmented, and degraded by land clearance and conversion by humans. Many remnants are also invaded by non-native plants and mammals, which can exacerbate biodiversity loss and impede ecosystem recovery. We examined the effects of non-native ground cover weeds and mammals on the seedling recruitment of native woody plants in lowland forests in northern New Zealand by following establishment over 2 years at sites experiencing different levels of weed cover, with or without supplemental seed addition, and with or without mammal exclusion. In general, native seedling recruitment was highest where seeds had been added and mammals excluded. Native seedling recruitment was negatively correlated with weed cover at sites invaded by Asparagus scandens or Tradescantia fluminensis, but only where seeds had been added. These results suggest that attempts to facilitate native seedling recruitment by sowing native seeds will be most successful where ground cover weeds and introduced mammals are low in abundance. Seedling recruitment was highest for Piper excelsum, Myrsine australis and Melicytus ramiflorus, so these species could be good options for lowland-forest restoration projects where ground cover weeds are present.