Corinne Watts

This review summarises the taxonomic status, morphology, physiology, ecology, plant communities, mycological, invertebrate and vertebrate interactions and human use of the New Zealand endemic tree Kunzea ericoides (A. Rich.) Joy Thomps. (kānuka) (Myrtaceae). While first treated as two species and later divided into ten species, recent comprehensive genetic analysis has shown that it is a single variable species. Kānuka ranges in size from small, multi‐stemmed trees about 4 m tall to one of the tallest angiosperms at over 30 m. It is a relatively long‐lived successional tree, tolerant of winter cold and drought and a wide range of soils. It is one of the few native trees that regenerates widely after fire and is abundant throughout most of New Zealand, including many northern islands. Its original disturbance‐related niche has greatly expanded as a result of deforestation since human settlement. We now live in the golden age of kānuka; it is probably more widespread and abundant now than it has ever been in the past. Kānuka tends to form monospecific stands through which other tree species regenerate, but this is dependent on climate and seed sources. Kānuka forests harbour a diverse mycological and invertebrate biota. Abundant flowering, seeding and invertebrate populations make it a highly suitable habitat for birds and reptiles. Once treated largely as a weed in agricultural landscapes or used for firewood, recent years have seen it increasingly valued for honey and essential oil production. Kānuka has also become pivotal to restoration projects through its ease of nursery propagation, rapid growth and canopy closure and tolerance of a wide range of situations, including vertebrate browsing. These same attributes make it a favoured Indigenous species for erosion‐control, especially on steeplands.

Introduction: Applied nucleation aims to restore degraded ecosystems efficiently by establishing vegetation patches that increase in biodiversity and extent through natural dispersal and facilitation. Although widely tested in terrestrial ecosystems, its long‐term outcomes in wetlands remain poorly understood, particularly how restored communities develop over time and how post‐restoration trajectories compare with reference ecosystems. Objectives: We evaluated outcomes after 21 years of an applied nucleation experiment to restore a mined restiad raised bog in northern New Zealand. Methods: Nuclei were established as raised peat islands (approximately 10 m diameter) and seeded with the early‐successional shrub mānuka ( Leptospermum repo ) in 2002. Vegetation composition and peat properties were assessed within nuclei and the surrounding matrix at three distances from an adjacent natural reference peatland. Nuclei plots were surveyed after 2, 9, and 21 years, while matrix and natural peatland plots were measured after 21 years. Results: Mānuka successfully established, followed by the establishment of peat‐forming restiad species bamboo rush ( Sporadanthus ferrugineus ) and wire rush ( Empodisma robustum ), the latter one of three species facilitated by mānuka. Beta diversity among nuclei increased over time, reflecting continued recruitment and increasing community heterogeneity. Plant community composition within nuclei became progressively more similar to the natural peatland, and after 21 years, nuclei supported higher diversity and greater compositional similarity to the natural peatland than did surrounding matrix areas, which also showed recovery toward the reference community. However, persistent differences in peat bulk density, water content, and nutrient concentrations revealed enduring legacies of mining disturbance. Conclusions: Applied nucleation can initiate ecological recovery in degraded peatlands. Establishment of early‐successional nurse species facilitates the return of peat‐forming plants and promotes recovery toward a reference community, even where disturbance legacies persist.

Sanctuary Mountain Maungatautari (SMM), New Zealand's largest pest‐fenced ecosanctuary, provides a unique opportunity to study invertebrate responses to mammal eradication. Beetles and wētā were monitored within the mouse‐free southern exclosure and in adjacent comparable forests on the mountain, within the predator‐proof fence (in 2004/05, then 2006/07 to 2012/13; n = 8 years), with methods and analyses repeated for monitoring in summer 2023/24 (1 year) and then compared across the 9 years. Data collected during 2004–2013 showed higher beetle species richness and abundance inside the southern exclosure in several earlier summers, with differences in patterns through time and among beetle size classes; the 2023/24 data revealed little difference between inside and outside. Beetle community composition changed following mammal eradication and then changed again with increasing mouse densities outside the southern exclosure. Wētā showed a stronger positive response, with consistently higher abundance inside the southern exclosure across multiple years and declines outside when mouse control ceased, supporting evidence that large Orthoptera benefit from mammal, particularly mouse, removal. Nineteen years after mammal eradication, invertebrate communities continue to show variable responses; these responses are influenced by both predation from recovering bird populations and persistent mice. The SMM dataset represents the longest‐running invertebrate monitoring in an ecosanctuary in New Zealand, providing critical insights into the long‐term impacts of pest mammal removal. Decadal resampling will be needed to track ongoing responses, with the next sampling scheduled for summer 2033/34.

The removal or exclusion of invasive mammals is a crucial strategy for protecting vulnerable biodiversity, particularly on islands. While eliminating invasive mammals has been shown to increase native species abundance and diversity, it remains unclear whether the ecosystem functions those species provide are also being restored. In particular, the restoration of ecosystem functions performed by invertebrates, such as litter decomposition, pollination and herbivory, is poorly understood. We test whether the removal of invasive mammals restores invertebrate‐mediated decomposition by measuring decomposition of a common native tree ( Melicytus ramiflorus ) within three paired ecosanctuary (all invasive mammals eradicated except mice) and non‐ecosanctuary sites across Aotearoa/New Zealand. Results demonstrated that ecosanctuaries had increased decomposition compared to non‐ecosanctuaries, but this was dependent on litterbag mesh type. Coarse mesh (which allowed access by some larger meso‐ and macrofauna) had greater decomposition in ecosanctuaries compared to non‐ecosanctuaries, but fine mesh had similar decomposition across both site types. Based on other studies of invertebrate diversity inside and outside ecosanctuaries, we suggest this result is largely due to more diverse and abundant detritivore communities within ecosanctuaries. We also detected fine‐scale differences in vegetation composition between ecosanctuaries and non‐ecosanctuaries, probably due to the exclusion of invasive browsing mammals from ecosanctuaries, which also may have influenced decomposition. Our findings suggest that the eradication of invasive mammals can restore an important ecosystem function driven by invertebrates, and we recommend that future studies examine whether other critical invertebrate‐mediated functions (e.g., predation and pest control, pollination) are also being restored.

The Mahoenui giant wētā (MGW), Deinacrida mahoenui (Insecta: Orthoptera), is an Aotearoa New Zealand endemic insect of conservation concern. Conservation management of this species includes a history of translocation to reduce extinction risk. However, translocations can create artificial bottlenecks which may reduce the genetic diversity of the translocated population, limiting their ability to adapt to future environmental change. We now have the opportunity to use genetic tools to assess the impacts of past translocations and use these to optimise current translocation approaches and develop methods for monitoring genetic diversity and future maintenance of diversity. Using a genotyping‐by‐sequencing approach, we found low levels of differentiation and population structuring between the source and one reintroduced population, and similar relatively low levels of genetic diversity in both populations. Informed by these results, we recommend that these populations be managed as a single unit by continuing with regular translocations creating gene flow to maintain genetic diversity.

The advent of mammal-resistant fences has allowed multi-species eradications of mammals from ecosanctuaries on the New Zealand mainland. However, maintaining eradication of house mice (Mus musculus) has proven difficult, and at some fenced reserves they are the only exotic mammal present and reach a high population density. Over 5 years we examined the impacts of mice alone on biodiversity at Sanctuary Mountain Maungatautari by comparing forest blocks with relatively high and low numbers of mice.

Predation by introduced mammals frequently limits abundance of New Zealand’s native invertebrates. We investigated responses of beetle and wētā communities to mammal eradication at two fenced forest sites at Maungatautari. Ground‐dwelling beetle abundance, but not species richness, increased inside the southern exclosure two years after all mammals were eradicated. In the next 5 years, when all mammals except mice were eradicated from all of Maungatautari, beetle abundance and species richness were frequently higher in the mouse‐free southern exclosure. Beetle community composition changed after mammal eradication, and over time with increasing mice densities outside the southern exclosure. Large, predatory, and native beetles showed the most differences between inside and outside the southern exclosure over some years. Wētā were more responsive to mammal removal than beetles. Wētā abundances both inside and outside the southern exclosure were similar when most mammals were eradicated and mice were controlled to low numbers. However, wētā declined in the following 2 years outside the southern exclosure when mouse abundance increased. Abiotic and biotic factors affecting the beetle and wētā communities are complex and interactions poorly understood. This study indicates that climate and predation by native fauna are likely to be important factors.

The effect of modifying New Zealand’s threatened peat bogs on invertebrate communities is poorly known, despite their susceptibility to disturbance and their ecological significance. Using Malaise traps, we surveyed and compared terrestrial invertebrates in a remnant modified bog (Moanatuatua) isolated in an agricultural landscape and a community in an intact large bog (Kopuatai) in New Zealand. On average, more invertebrates were caught in the modified bog than in the intact bog. In addition, observed mean abundances for Diptera were higher at the modified bog. In contrast, total and geometric mean abundance of Coleoptera was significantly lower in the modified bog compared to the intact bog. We found no evidence of differences in species richness of Coleoptera, Lepidoptera, Diptera, Hymenoptera between the two bogs. Introduced species were more common in the modified bog. Ordination results indicated a difference in invertebrate community composition between the two bogs, and in addition the modified bog plots separated according to their distance from the wetland edge. Our results indicate that, within a modified isolated bog, native invertebrates can survive, and that some specialised and threatened species can thrive. However, the lower proportion of native Diptera and Lepidoptera taxa abundance in the modified bog is reason for concern.