fragmentation

The fragmentation of forested environments in Aotearoa | New Zealand has resulted in many small, geographically isolated populations that face an increased risk of extinction. However, population extinction itself, and its proximate causes, are rarely witnessed scientifically. As part of a broader study, we assessed the population status of a remnant kakaruai (South Island robin; Petroica australis) population within the Ōtepoti | Dunedin area.

Small patches of habitat for indigenous species that remain in developed landscapes are predicted to lose species over time as extinction debts are paid off and to become transformed by spillover from intensive land uses. In December 2020 we searched for plants of three inland South Island-endemic species of Lepidium (Brassicaceae; L. kirkii, L. sisymbrioides, and L. solandri) at previously known locations in Central Otago, the Waitaki Valley, the Mackenzie Basin, and Kura Tāwhiti (Castle Hill, North Canterbury).

Effective biodiversity conservation in lowland New Zealand requires an understanding of the relative benefits of managing impacts of native forest loss versus controlling invasive species. We used bird count data from 195 locations across mainland northern New Zealand to examine how the abundance and richness of native forest birds varied across wide gradients of native forest cover (c. 0–100%) and intensity of invasive species control (‘eradication’, ‘high-intensity rat and possum’, ‘low-intensity rat and possum’, ‘periodic possum’ and ‘none’).

The distribution and prevalence in New Zealand of adventive detritivores in native forest remnants, and of native detritivores in pine plantations, are not well known. We investigated whether forest type (small urban native remnants, large remote native remnants, and pine) and plot location (edge plot vs centre plot) influenced the abundance and community composition of native and adventive detritivores (Diplopoda, Isopoda, and Amphipoda) in forests of a modified landscape in the lower North Island of New Zealand.

Positive effects of fragmentation on plant reproduction are uncommon; in a literature review we found significant negative effects on fruit or seed set for 50 plant species, compared to 26 species showing no effect, and only nine affected positively. One of these is the declining New Zealand mistletoe Peraxilla tetrapetala (Loranthaceae), and here we investigate the mechanism of this positive effect. P. tetrapetala requires visits from native bird or bee pollinators to produce fruit.

Vegetation was sampled in kahikatea (Dacrycarpus dacrydioides)-dominant forest fragments having different recovery periods since grazing ceased in the Waikato region, North Island, New Zealand. Changes in vegetation were modeled against recovery periods ranging from 0–74 y and in relation to position within fragment (edge or interior). Indigenous plant species richness increased and adventive plant species (mostly pasture herbs) richness declined with increasing recovery period; small tree and sapling density and seedling ground cover increased.

Te Paki Ecological District in Northland is regarded as a New Zealand biodiversity hotspot, but habitat loss and forest fragmentation have adversely affected many of its endemic species. We investigated the distribution and habitat associations of Mecodema tenaki (Coleoptera: Carabidae), a Te Paki endemic ground beetle whose threat status was recently changed from ‘Nationally Critical’ to ‘Declining’. Manual searching and pitfall trapping (live-capture and lethal) were used to detect the species at 46 sites in three habitat types: native forest, pine plantation and shrubland.

Restoration of native forest vegetation in urban environments may be limited due to isolation from native seed sources and to the prevalence of exotic plant species. To investigate urban seed availability we recorded the composition of seed rain, soil seed banks and vegetation at native forest restoration plantings up to 36 years old in Hamilton City and compared these with naturally regenerating forest within the city and in a nearby rural native forest remnant.

Holdaway (1989) described three phases of historical extinctions and declines in New Zealand avifauna, the last of which (Group III, declining 1780–1986) was associated with European hunting, habitat clearance, and predation and competition from introduced European mammals. Some forest bird species have continued to decline since 1986, while others have increased, usually after intensive species-specific research and management programmes.

Small isolated patches of native forest surrounded by extensive pastoral grasslands, characteristic of many New Zealand rural landscapes, represent an important reservoir of lowland biodiversity. Improved management of them is a major focus of biodiversity conservation initiatives in New Zealand. We quantified the long-term impacts of grazing on indigenous forest remnants in hill country at Whatawhata, western Waikato, North Island. Structure and composition were compared between forest fragments grazed for >50 years and nearby ungrazed continuous forest.