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Kahikatea (Dacrycarpus dacrydioides) is a tall, wetland‐tolerant native podocarp tree that has potential for restoration of New Zealand wetlands currently dominated by invasive Grey willow (Salix cinerea). We investigated methods to jump‐start establishment of Kahikatea saplings in the Ramsar‐listed Whangamarino Wetland. Treatments involved planting saplings after full herbicide clearance of the willow canopy (FULL), partial herbicide clearance of the canopy (PARTIAL), and manual cutting of light wells (MANUAL). Saplings were planted as individuals or clusters of seven. Treatment plots were established in 2015 and monitored until 2020. Despite Kahikatea being considered a "light‐demanding" species, saplings grew best in the PARTIAL treatment which had the lowest ambient light levels (x̄=32% of non‐intercepted sunlight). PARTIAL treatment saplings were estimated to require 24–36 years to reach the height of the surrounding willow canopy if they maintained similar growth rates. Preconditioning saplings by soaking roots before planting provided a growth advantage in the PARTIAL treatment plots, whereas nonconditioned plants grew better in the higher‐light MANUAL and FULL plots. No benefit was found for cluster planting. Restoration toward a native Kahikatea‐dominated forest will be contingent on saplings reaching willow canopy height before the faster‐growing willows reestablish, or periodic management of willows to maintain light levels above the compensation point for continued growth. Ultimately, the utility of this approach depends on what on‐going facilitation is required and whether seedlings subsequently produced by these emergent podocarp "islands" are able to jump‐start a long‐term change in the successional trajectory of the surrounding willow‐dominated wetland. [ABSTRACT FROM AUTHOR]

We compared biocontrol beetles and manual clearing of tradescantia in forest remnants invaded by tradescantia (Tradescantia fluminensis Vell.) on the agriculturally modified Hikurangi floodplain, northern New Zealand, to inform best practice in enhancing native biodiversity. Four forest remnant study sites were used: two on dairy farms and two protected in a reserve. We assessed tradescantia biomass and cover as indicators of biocontrol effectiveness in the short term, and composition and seedling establishment for effectiveness in the longer term. We found the biocontrol treatment (a combination of tradescantia beetles Neolema ogloblini, Neolema abbreviata, and Lema basicostata) was slow in reducing tradescantia biomass and had little effect in promoting regeneration of native forest species after 3 years. Beetle feeding damage was significantly higher at the biocontrol sites; however, tradescantia biomass or cover was not significantly lower. Although tradescantia biomass in the biocontrol treatment was decreasing, several more years would probably be required for beetle populations to increase and reduce biomass sufficiently to facilitate survival of native seedlings. Results between sites were variable, although dairy farm sites had overall higher nutrient status with higher total potassium levels, and lower nitrogen/phosphorus ratios, and generally higher tradescantia biomass. Manual clearing (‘handclear’) of tradescantia increased vascular species richness but was much more labour intensive and required ongoing management of resprouts. Handclear plots also had lower soil water content than control (means = 36% dry weight, 49% dry weight, respectively), a wider range of daily temperatures, and high species losses (as well as gains). Species losses were probably exacerbated by the greater environmental extremes caused by removal of the tradescantia living mulch, and the incomplete recovery of ground cover vegetation and microclimate suitable for seedling regeneration. Biodiversity benefits are likely to accrue slowly following the introduction of biocontrol agents; longer-term, these should prove more cost-effective than handclear. [ABSTRACT FROM AUTHOR]

Much land has been cleared of indigenous forest for pastoral agriculture worldwide. In New Zealand, the clearance of indigenous forest on hill country has resulted in high food production, but waterways have become turbid, with high nutrient and E. coli concentrations. A range of on-farm mitigations are available, but it is unclear how they should be applied catchment-wide. We have developed a catchment-scale model that integrates economics with ecosystem services to find a better balance between agriculture and nature. In the upper Wairua catchment, Northland, if three actions are prioritised—(1) keeping stock out of streams, (2) constructing flood retention bunds in first-order catchments, and (3) planting trees on highly erodible land—then sediment loads, E. coli levels, and flooding are significantly reduced. Implementing these actions would cost approximately 10% of catchment net revenue, so it is feasible with a combination of regulation and subsidy. Many catchments in New Zealand are primarily pastoral agriculture, as in other countries (in North and South America, Australasia, and the United Kingdom), and would benefit from the analysis presented here to guide development along sustainable pathways. While pastoral agriculture typically stresses waterways, with increased sedimentation and freshwater contaminants, much can be done to mitigate these effects with improved farm and riparian management. [ABSTRACT FROM AUTHOR]

In agricultural landscapes, free-water surface flow wetlands (FWS) are constructed mainly to improve water quality; however, their contribution to biodiversity conservation is increasingly recognised. To inform biodiversity management in FWS treating agricultural runoff, we surveyed the vegetation and fauna assemblages in five established FWS in a lowland, pastoral landscape in the central North Island, New Zealand. The FWS had been established for between 3 and 19 years, planted with a restricted range of native plant species, and fenced to exclude livestock access. Larger wetlands hosted significantly more plant and mammal species. However, other than wetland size, we found few other significant relationships between wetland habitat, landscape characteristics, and measures of biodiversity (total species, proportion of native species, number of wetland specialists, or threatened species). We recorded one-hundred and thirteen plant, twenty bird, five mammal, eighty-five terrestrial invertebrates, forty-seven aquatic invertebrates, six fish, and two amphibian species inhabiting the FWS. Native species comprised 96% of the total aquatic invertebrate fauna identified. For other taxa, native flora and fauna accounted for half or less than half of all species identified: 53% terrestrial invertebrates, 50% fish, 45% birds, 32% plants, and 0% amphibian and mammal species. Few wetland specialists (aquatic or wetland-adapted) or threatened native species were detected, probably reflecting the limited range of wetland plant species in initial plantings and the difficulties native taxa face when colonising new habitat where potential reservoirs of colonist species are also depauperate or too distant. FWS support native biodiversity, but further enhancements may require active management of exotic and pest species to minimise competition or predation on native species. [ABSTRACT FROM AUTHOR]

The genus Empodisma comprises two species that are ecologically important in wetland habitats. Empodisma gracillimum is restricted to south-western Australia, whereas E. minus is found in Tasmania, eastern Australia and New Zealand. We sequenced three cpDNA genes for 15 individuals of Empodisma sampled from throughout the range of the species. The results support an Australian origin for Empodisma sometime during the late Oligocene to early Miocene with more recent dispersal, colonization and diversification in New Zealand. We recovered six genetically distinct maternal lineages: three E. gracillimum haplotypes corresponding to the three accessions in our analysis, a wide-ranging E. minus haplotype found in eastern Australia and Tasmania, an E. minus haplotype found in New Zealand from Stewart Island to approximately 38° S latitude on the North Island, and a distinct haplotype restricted to the North Island of New Zealand north of 38° S latitude. The Eastern Australian and New Zealand haplotypes of E. minus were supported by only one cpDNA gene, and we felt the relatively minor morphological differences and the small amount of genetic divergence did not warrant taxonomic recognition. However, we recommend that the northern New Zealand haplotype should be recognized as the new species Empodisma robustum and provide descriptions and a key to the species of Empodisma. Monophyly of E. robustum is supported by all three cpDNA genes. Empodisma robustum can be distinguished from E. gracillimum and E. minus by its robust growth stature and distinct ecology. It is typically eliminated by fire and re-establishes by seed (seeder strategy), whereas E. minus and E. gracillimum regrow after fire (sprouter strategy). [ABSTRACT FROM AUTHOR]

Empodisma minus and Sporadanthus ferrugineus (both Restionaceae) coexist in New Zealand raised bogs, yet Sporadanthus have significantly more depleted 15N natural abundance signatures than coexisting Empodisma. Their root systems are spatially separated with Empodisma having a thick surface layer of about 50 mm of cluster roots overlying the deeper Sporadanthus roots. We hypothesized this root displacement allows Empodisma to preferentially access the primary N input from rainfall, thus establishing niche separation, and tested this using tracer stable isotopes. We aerially applied 1.6 mmol m−2 of 15N as (NH4)2SO4 chased by deionized water to simulate a rainfall event of 34 L m−2. Root/peat matrix cores were harvested after 5 h and analysed for 15N uptake. Approximately 80% of the tracer applied was recovered in the cores, with 90% of this recovered in the upper Empodisma cluster root layer. Seven weeks after application, young shoots of Empodisma were significantly enriched (mean δ15N = +7.21‰; reference = −0.42‰), whereas those of coexisting Sporadanthus were not (mean δ15N = −2.76‰; reference = −4.24‰). However, we were unable to quantify the 15N uptake because of the dilution effect of the large biomass. We calculated the contribution of biological nitrogen fixation as a possible alternative source of N in achieving niche separation. The acetylene reduction assay showed minor amounts of nitrogenase activity are associated with Empodisma and Sporadanthus roots (equivalent to 0.045 ± 0.019 and 0.104 ± 0.017 kg N ha−1 year−1 respectively). Our results suggest that the species acquire nutrients from different rooting zones, with Empodisma accessing nutrients at the surface from rainfall and Sporadanthus accessing nutrients from mineralization in deeper peat layers. Such niche differentiation probably facilitates species coexistence and may provide a mechanism for slowing the rate of competitive displacement during long-term succession. [ABSTRACT FROM AUTHOR]

Foliar δ15N, %N and %P in the dominant woody and herbaceous species across nutrient gradients in New Zealand restiad (family Restionaceae) raised bogs revealed marked differences in plant δ15N correlations with P. The two heath shrubs, Leptospermum scoparium (Myrtaceae) and Dracophyllum scoparium (Epacridaceae), showed considerable isotopic variation (−2.03 to −15.55‰, and −0.39 to −12.06‰, respectively) across the bogs, with foliar δ15N strongly and positively correlated with P concentrations in foliage and peat, and negatively correlated with foliar N:P ratios. For L. scoparium, the isotopic gradient was not linked to ectomycorrhizal (ECM) fractionation as ECMs occurred only on higher nutrient marginal peats where 15N depletion was least. In strong contrast, restiad species ( Empodisma minus Sporadanthus ferrugineus, S. traversii) showed little isotopic variation across the same nutrient gradients. Empodisma minus and S. traversii had δ15N levels consistently around 0‰ (means of −0.12‰ and +0.15‰ respectively), and S. ferrugineus, which co-habited with E. minus, was more depleted (mean −4.97‰). The isotopic differences between heath shrubs and restiads were similar in floristically dissimilar bogs and may be linked to contrasting nutrient demands, acquisition mechanisms, and root morphology. Leptospermum scoparium shrubs on low nutrient peats were stunted, with low tissue P concentrations, and high N:P ratios, suggesting they were P-limited, which was probably exacerbated by markedly reduced mycorrhizal colonisations. The coupling of δ15N depletion and %P in heath shrubs suggests that N fractionation is promoted by P limitation. In contrast, the constancy in δ15N of the restiad species through the N and P gradients suggests that these are not suffering from P limitation. [ABSTRACT FROM AUTHOR]

Whether nitrogen-fixing plants facilitate or inhibit species change in primary succession is best resolved by examining their impacts throughout the plant's entire life cycle from arrival to senescence. We experimentally examined two aspects of the successional impacts of a nitrogen-fixing shrub, Coriaria arborea, on Mt. Tarawera, a volcano in New Zealand: factors limiting Coriaria colonization and impacts of Coriaria-induced soil changes on a later successional tree, Griselinia littoralis. Coriaria germination was promoted by artificial wind protection and by the presence of heath shrubs. Transplanted Coriaria seedlings survived only if nodulated with Frankia, and the addition of Coriaria-enriched soils slowed Coriaria seedling growth and did not improve seedling survival. This explained why Coriaria seedlings were found mostly in protected habitats away from adult Coriaria, and suggested that Coriaria thickets are not self-replacing. Coriaria increased soil fertility by developing a 4 cm thick organic soil horizon that was richer in nitrogen (tenfold) and phosphorus (threefold) than pre-Coriaria stages. These soil changes resulted in three- to sixfold increases in growth of Griselinia when it was grown in Coriaria-enriched soils in a glasshouse. Coriaria's net effect on primary succession is facilitative, but the establishment of Coriaria is itself facilitated by the amelioration of the physical habitat by earlier colonists, suggesting facilitation is important throughout the life cycle of Coriaria. Sequential facilitative events determine the order of species replacements in this study but inhibition, linked to the developmental stages of Coriaria, may determine... [ABSTRACT FROM AUTHOR]