New Zealand’s formerly extensive lowland native forests have been comprehensively cleared or modified, and large areas of secondary-growth vegetation have subsequently established. These areas are comprised of native, exotic, and mixed tree and shrub species assemblages. The mature-phase canopy and emergent tree species representative of pre-human New Zealand forests are often rare or locally extinct in these forests, indicating negative ramifications for long-term biodiversity conservation and ecosystem service provision, especially such as carbon sequestration.
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.
The dominant native woody species forming early-successional vegetation on formerly forested sites in lowland New Zealand were kānuka (Kunzea ericoides) and mānuka (Leptospermum scoparium) (Myrtaceae). These have been replaced extensively by gorse (Ulex europaeus, Fabaceae), a naturalised species in New Zealand. Because gorse typically gives way to native broadleaved (angiosperm) forest in about 30 years, it is often considered desirable for facilitating native forest restoration.