Options for enhancing forest biodiversity across New Zealand's managed landscapes based on ecosystem modelling and spatial design

In most regions of the world removal of environmental stress facilitates regeneration of native plants and habitats. However, in many of New Zealands modified landscapes, exotic species are likely to respond first to any reduction in stress because these fast-growing species are prevalent in local vegetation and dominate seed banks. Given the trend in agriculture towards intensive management on larger units, the indigenous character in New Zealand landscapes is being marginalised and there is the risk that further reduction in visibility of native vegetation may be perpetuated by a growing familiarity and identification with ubiquitous exotic species. Alternative landscapes, based on an understanding of ecosystem processes, need to be explored if biodiversity goals set by international convention and national resource management law are to be achieved. This study provides a set of predictions and pathways, backed by field observations, to underpin a restoration strategy at patch to landscape scales. A forest model, LINKNZ, is employed to simulate species succession under New Zealand conditions. The incorporation of disturbance regimes and species dispersal processes in the model permits a wide range of scenarios to be investigated encompassing indigenous forest development, exotic species interactions with indigenous forest ecosystems, management of mixed introduced-indigenous forests, and landscape dynamics. The results illustrate an approach that identifies potential biosecurity threats and provides additional options for integrating nature and production in New Zealands rural and urban landscapes.     

The role of blackbirds (

The naturalised European blackbird (Turdus merula) is the most widely distributed avian seed disperser in New Zealand. Together with the native silvereye (Zosterops lateralis) they are the major seed dispersers over large areas of New Zealand. I review the international literature on aspects of the ecology and behaviour of blackbirds relevant to their potential for dispersing weeds in New Zealand. Blackbirds eat a wide range of native and exotic fruit including many naturalised species. Their habitat preferences and behaviour result in germinable seeds being deposited in a range of sites, particularly in shrubby habitats, where seedling establishment is likely. Most seeds will be deposited within 50 m but some may be carried a kilometre or more to develop new invasive loci. Blackbirds therefore probably make a major contribution to the development of novel plant communities of naturalised woody weeds. These communities provide fruit more suited to non- endemic native birds and naturalised birds, than to endemic birds. The relative contribution of blackbirds and silvereyes to seed dispersal of native and exotic species requires investigation. The outcome may suggest potential for managing blackbirds as a vector of weed invasions.     

Differences in Earthworm Densities and Nitrogen Dynamics in Soils Under Exotic and Native Plant Species

Previous studies of the invasion of two exotic plants – Berberis thunbergii and Microstegium vimineum – in hardwood forests of New Jersey have shown a significant increase of pH in soils under the invasive plants as compared with soils from under native shrubs (Vaccinium spp). We present a further investigation of soil properties under the exotic plants in question. We measured the densities of earthworms in the soil under the two exotics and the native shrubs in three parks in New Jersey. In the same populations we also measured the extractable ammonium and nitrate in the top 5 cm of the soil, as well as the respiration of the soils and the potential rates of mineralization (aerobic lab incubation). In addition, we measured the nitrate reductase activity in leaves of the two exotic plants and several native shrubs and trees. Although there were differences between parks, we observed significantly higher earthworm densities in the soil under the exotic species. The worms were all European species. Soil pH, available nitrate and net potential nitrification were significantly higher in soils under the two exotic species. In contrast, total soil C and N and net ammonification were significantly higher under native vegetation. Nitrate reductase activities were much higher in the leaves of exotic plants than in the leaves of native shrubs and trees. Changes in soil properties, especially the change in nitrogen cycling, associated with the invasion of these two plant species may permit the invasion of other weedy or exotic species. Our results also suggest that even if the two exotic species were removed, the restoration of the native flora might be inhibited by the high nitrate concentrations in the soil.     

Identifying Native Vegetation for Reducing Exotic Species during the Restoration of Desert Ecosystems

There is currently much interest in restoration ecology in identifying native vegetation that can decrease the invasibility by exotic species of environments undergoing restoration. However, uncertainty remains about restoration's ability to limit exotic species, particularly in deserts where facilitative interactions between plants are prevalent. Using candidate native species for restoration in the Mojave Desert of the southwestern U.S.A., we experimentally assembled a range of plant communities from early successional forbs to late‐successional shrubs and assessed which vegetation types reduced the establishment of the priority invasive annuals Bromus rubens (red brome) and Schismus spp. (Mediterranean grass) in control and N‐enriched soils. Compared to early successional grass and shrub and late‐successional shrub communities, an early forb community best resisted invasion, reducing exotic species biomass by 88% (N added) and 97% (no N added) relative to controls (no native plants). In native species monocultures, Sphaeralcea ambigua (desert globemallow), an early successional forb, was the least invasible, reducing exotic biomass by 91%. However, the least‐invaded vegetation types did not reduce soil N or P relative to other vegetation types nor was native plant cover linked to invasibility, suggesting that other traits influenced native‐exotic species interactions. This study provides experimental field evidence that native vegetation types exist that may reduce exotic grass establishment in the Mojave Desert, and that these candidates for restoration are not necessarily late‐successional communities. More generally, results indicate the importance of careful native species selection when exotic species invasions must be constrained for restoration to be successful.     

Invasion of exotic earthworms into ecosystems inhabited by native earthworms

The most conspicuous biological invasions in terrestrial ecosystems have been by exotic plants, insects and vertebrates. Invasions by exotic earthworms, although not as well studied, may be increasing with global commerce in agriculture, waste management and bioremediation. A number of cases has documented where invasive earthworms have caused significant changes in soil profiles, nutrient and organic matter dynamics, other soil organisms or plant communities. Most of these cases are in areas that have been disturbed (e.g., agricultural systems) or were previously devoid of earthworms (e.g., north of Pleistocene glacial margins). It is not clear that such effects are common in ecosystems inhabited by native earthworms, especially where soils are undisturbed. We explore the idea that indigenous earthworm fauna and/or characteristics of their native habitats may resist invasion by exotic earthworms and thereby reduce the impact of exotic species on soil processes. We review data and case studies from temperate and tropical regions to test this idea. Specifically, we address the following questions: Is disturbance a prerequisite to invasion by exotic earthworms? What are the mechanisms by which exotic earthworms may succeed or fail to invade habitats occupied by native earthworms? Potential mechanisms could include (1) intensity of propagule pressure (how frequently and at what densities have exotic species been introduced and has there been adequate time for proliferation?); (2) degree of habitat matching (once introduced, are exotic species faced with unsuitable habitat conditions, unavailable resources, or unsuited feeding strategies?); and (3) degree of biotic resistance (after introduction into an otherwise suitable habitat, are exotic species exposed to biological barriers such as predation or parasitism, “unfamiliar” microflora, or competition by resident native species?). Once established, do exotic species co-exist with native species, or are the natives eventually excluded? Do exotic species impact soil processes differently in the presence or absence of native species? We conclude that (1) exotic earthworms do invade ecosystems inhabited by indigenous earthworms, even in the absence of obvious disturbance; (2) competitive exclusion of native earthworms by exotic earthworms is not easily demonstrated and, in fact, co-existence of native and exotic species appears to be common, even if transient; and (3) resistance to exotic earthworm invasions, if it occurs, may be more a function of physical and chemical characteristics of a habitat than of biological interactions between native and exotic earthworms.     

Causes and consequences of changes to New Zealand?s fungal biota

This paper briefly reviews advances in knowledge of the non-lichenised fungi of New Zealand over the past 25 years. Since 1980, the number of species recorded from New Zealand has doubled, and molecular techniques have revolutionised studies on fungal phylogeny and our understanding of fungal distribution, biology and origins. The origins of New Zealand?s fungi are diverse; a few appear to be ancient, whereas many have arrived in geologically more recent times following trans-oceanic dispersal. Some of these more recent arrivals have evolved subsequently to form local endemic species, while others may be part of larger populations maintained through regular, trans-oceanic gene flow. Although questions remain about which fungi truly are indigenous and which are exotic, about one-third of the fungi recorded from New Zealand are likely to have been introduced since human settlement. While most exotic species are confined to human-modified habitats, there are some exceptions. These include species with potential to have significant impacts at the landscape scale. Examples from saprobic, pathogenic, endophytic and ectomycorrhizal fungi are used to discuss the factors driving the distribution and dispersal of New Zealand?s fungi at both global and local scales, the impact that historical changes to New Zealand?s vascular plant and animal biota have had on indigenous fungi, and the broader ecological impact of some of the exotic fungal species that have become naturalised in native habitats. The kinds of fungi present in New Zealand, and the factors driving the distribution and behaviour of those fungi, are constantly changing. These changes have occurred over a wide scale, in both time and space, which means New Zealand?s indigenous fungi evolved in response to ecological pressures very different from those found in New Zealand today.     

Post-pastoral changes in composition and guilds in a semi-arid conservation area, Central Otago, New Zealand

Changes in the vegetation of Flat Top Hill, a highly modified conservation area in semi;arid Central Otago, New Zealand, are described four years after the cessation of sheep and rabbit grazing. Unusually moist weather conditions coincide with the four-year period of change in response to the cessation of grazing. Between 1993 and 1997, the average richness and diversity (H') of species increased, and the average proportion of native species decreased significantly. The vegetation was significantly richer in exotic annual and perennial grass species, exotic perennial forbs, exotic woody species and native tussock grasses in 1997 than in 1993. Eight response guilds of species are identified. Most "remnant" native shrubs and forbs were stable, in that they remained restricted to local refugia and showed little change in local frequency. However, taller native grass species increased, some locally, and others over wide environmental ranges. Rare native annual forbs and several native perennial species from "induced" xeric communities decreased, and this may be a consequence of competition from exotic perennial grasses in the absence of grazing. The invasive exotic herb Sedum acre decreased in abundance between 1993 and 1997, but several other prominent exotic species increased substantially in range and local frequency over a wide range of sites. Exotic woody species, and dense, sward-forming grasses are identified as potential threats to native vegetation recovery.     

Biomass allocation in subantarctic island megaherbs,

The distribution of the indigenous New Zealand megascolecid earthworm Octochaetus multiporus (Beddard) in hill pastures of different fertilities in the southern North Island of New Zealand, and the population density throughout a year are described. Octochaetus multiporus was most numerous in soils of low to moderate fertility. High fertility soils had a similar population density to that of an adjacent area of native forest, indicating that the exotic pasture environment can favour Octochaetus multiporus in some circumstances. Population density of Octochaetus multiporus was best correlated with soils which were moist in summer. There was no well defined breeding season for this species, mature and recently hatched individuals being found in most months of the year. Octochaetus multiporus is a deeper burrowing indigenous earthworm species which is successful in an exotic environment. In pastures which have moist soils in summer, this species may be improving soil structure and root penetration in the absence of deep burrowing introduced lumbricid earthworms.     

The vegetation of Flat Top Hill: An area of semi-arid grassland/shrubland in Central Otago, New Zealand

An account is given of the vegetation of Flat Top Hill, in the driest part of semi-arid lowland Central Otago, New Zealand. Although highly modified, the area was acquired for conservation in 1992, following almost 150 years of pastoral use. The vegetation was sampled in a composite scheme using permanent monitoring sites placed to include the majority of habitats and communities present. A number of environmental factors were measured in each sample. Native species comprise 53% of the vascular flora of the area (211 species). From multivariate analyses of the data collected over three seasons, fourteen 'communities' are recognised. Although there are few constant or faithful species, strong relationships are shown with certain environmental parameters. Moisture stress is the major environmental influence on the vegetation; soil depth and past disturbance are secondary determinants. The communities differ by a factor of 10 in vascular species richness; the richest communities, and those with the greatest native component, are those around rock tors. Many of the communities present have not been reported from other vegetation surveys in Central Otago Moisture stress at xeric sites in the dry core of the region has excluded some exotic species, and allowed the survival of the native component, including three tiny spring ephemerals. Near elimination of grazing, as a result of reservation, will probably lead to an increase in the cover of taller, palatable exotic grasses and Thymus vulgaris, which may threaten the survival of some native species. Optimum management, for recovery or persistence of native species, may comprise exclusion of grazers in some areas, but continuity of grazing in others.     

A remnant New Zealand carr

Carr vegetation was once extensive in New Zealand. It can be divided into Cordyline australis I Carex secta carr, comprising an open wood with scattered large herbs and an abundance of Carex species, and podocarp carr, dominated by tall conifers. Both have been almost eliminated by agricultural development. We studied a remnant of Cordyline australis I Carex secta carr in South Island, which graded at one end into salt marsh. Eight communities were recognized, including one pure salt marsh and two more with saline influence. Near the stream that provided moisture and alluvium for the area were herbaceous communities. In the poorly-drained area away from the stream were communities dominated by shrubs and small trees. The soil environment is similar to that of many European carrs, though generally less organic. A number of the exotic species are also found in European carrs.     

The diversity and origin of exotic ants arriving in New Zealand via human-mediated dispersal

The number of exotic ant species being dispersed to new regions by human transportation and the trade pathways responsible for this are poorly understood. In this study, the taxonomic diversity, trade pathways, and origin of exotic ants intercepted at the New Zealand border were examined for the period 1955–2005. Overall, there were a total 4355 interception records, with 115 species from 52 genera. The 10 most frequently intercepted genera, and the 20 most frequently intercepted species contributed > 90% of all records. Many of the species frequently intercepted are regarded as invasive species, and several are established in New Zealand. The most intercepted species was Pheidole megacephala . Despite a relatively low trade relationship, a high proportion (> 64%) of the exotic ants which were intercepted originated from the Pacific region. However, the majority of species intercepted from the Pacific was exotic to the region (71%), or to a lesser extent, wide-ranging Pacific native species. No endemic species from the Pacific were intercepted. The effectiveness of detecting exotic ant species at the New Zealand border ranged from 48–78% for different trade pathways, indicating a number of species remain undetected. Trade routes associated with specific geographical regions represent a major filter for the arrival of exotic ant species. Despite the importance of the Pacific as a frequent pathway, we suggest that the future establishment of exotic ant species in New Zealand is likely to be mitigated by a renewed focus on trade routes with cool temperate regions, particularly Australia.     

The spread and distribution of terrestrial planarians (Turbellaria: Tricladida: Geoplanidae) within New Zealand

The New Zealand flatworm, Arthurdendyus triangulatus (formerly Artioposthia triangulata) has become established in the British Isles and the Faroe Islands and its human-mediated spread within Northern Ireland and Scotland is well documented. The geographical distributions within New Zealand of it and two related species, A. australis and A. testacea have always been assumed to reflect the natural distribution patterns. However, an analysis of the vegetation groups where the flatworms are presently found suggests that within New Zealand the distributions of endemic terrestrial planarians have been extended significantly by human intervention. Delineation of present distribution patterns of these species within New Zealand may lead to a better understanding of their potential distribution in other countries if they ever became established in them. Such extensions of ranges of New Zealand endemics within the country have implications for biodiversity analyses.     

Can natural enemies of current insect pests provide biotic resistance to future pests?

1. Economic pests jeopardize agricultural production worldwide. Classical biological control, comprising the import of exotic natural enemies to control target pest populations, has a successful history in many countries. However, little is known about how these natural enemies contribute to the suppression of pests that are yet to arrive. Biotic resistance theory, though, posits that communities resist species invasions as a result of natural enemies.
2. We assessed the potential of the resident exotic parasitoid wasp fauna in New Zealand (intentionally‐introduced biological control agents and unintentionally‐introduced species) to provide biotic resistance against possible future pests. A dataset was generated containing resident exotic parasitoid species (Ichneumonoidea: Braconidae; Ichneumonidae) in New Zealand, as well as their known global host ranges and the pest status of host species, to infer the potential for biotic resistance.
3. The known exotic ichneumonoid fauna in New Zealand comprises 65 species. These species associate with 107 host species in New Zealand, of which 54 species are pests. However, the current exotic species could potentially suppress 442 pest species not yet occurring in New Zealand.
4. This approach could be used to inform pest management programmes worldwide. Future research should consider how biotic resistance from the established parasitoid fauna can be used to inform specific decisions with respect to classical biological control.

     

Community reassembly: a test using limestone grassland in New Zealand

To examine community reassembly, we sampled grasslands on calcareous soil (4%–24% CaCO₃) in New Zealand that were largely composed of species introduced from Britain. We tested whether the British species had reassembled on New Zealand limestone into the same communities as they form on limestone in Britain. The vegetation of six New Zealand sites was sampled, each with ten 2 × 2 m quadrats that followed the standard methodology of the British National Vegetation Classification (NVC). Analysing species presence and cover using program TableFit with the full database of British species, the New Zealand species assemblages gave poor to moderate fits (40%–72%) to the communities of the NVC, and even then not to calcareous grassland, though one site did fit to a calcareous spring community. The poor fits can be partly attributed to the absence from New Zealand of many British calcareous-specialist species. On omitting from the NVC database all species not present in New Zealand, the fits increased somewhat to 48%–77%. Using this modified database, two sites fitted British calcareous grassland communities. These two sites are on thinner soil (<10 cm depth), under lower rainfall. Where fits were obtained to calcareous communities, the environment of the community in Britain matched very well that of the New Zealand site. It is concluded that environmental and perhaps biotic filtering has been strong enough in some sites to assort alien species into the same species assemblages as they form in their native range, indicating the Deterministic model of community structure. However, the absence of some species has prevented full reassembly.     

A vegetation zonation from saltmarsh to riverbank in New Zealand

Abstract. Brackish riverbank marshes have been little studied. Therefore, a plant community sequence was sampled from saltmarsh to near-freshwater riverbank marsh on a number of disjunct marshes along the Taieri River, Otago, New Zealand, from near the mouth to 9 km inland. Salinity decreased steadily upstream, though the actual values were very different on two days sampled. Ten communities are recognised. The major vegetation zonation was upshore more than upstream, though there were several interactions between the upshore and upstream gradients. Few species, if any, were restricted to the mid reaches of the length of river sampled. There was only a very slight upshore increase in species richness, and no trend upstream. Sequences of communities occurred upshore on all marshes, but the sequence differed, even within a marsh. Species were assorted into communities in different ways from those of marine marshes in the area. Some species, native and exotic, occupied different beta-niches from those they occupied in other countries. Individualistic community structure is inferred.     

A comparison of realised niche relations of species in New Zealand and Britain

Summary Many plant species prominent in the native vegetation of the dry shingle banks at Dungeness (Britain) are also prominent as exotics in the dry Upper Clutha catchment (New Zealand). To examine the realised niche relations of these species, vegetation was sampled in the two areas. Inverse classification and ordination were used to determine the relative beta niches of the species in the two areas. There was little agreement; it seems that the exotic species in the Upper Clutha were pre-adapted to different niches from those in their native range.     

Current and Potential Roles of Soil Macroinvertebrates (Earthworms,Millipedes, and Isopods) in Ecological Restoration

Soil macroinvertebrates have a considerable impact on soil functions important to the restoration process, such as decomposition; yet, soil organisms have received relatively little attention in restoration ecology in terms of their applicability as agents of restoration. Here, we review how large obligate detritivores (earthworms, millipedes, and isopods) have been used to accomplish restoration goals, assess restoration progress, and function as bioindicators. Patterns of detritivore community succession and how these communities are themselves restored during restoration of perturbed ecosystems are also discussed. We conclude with a discussion of increased utilization of these taxa in future and ongoing restoration projects as well as the outreach activities that should be associated with use of these organisms.     

Molecular evidence for bicontinental hybridogenous genomic constitution in Lepidium sensu stricto (Brassicaceae) species from Australia and New Zealand

Lepidium sensu stricto (s.s.) (Brassicaceae) (ca. 150 species) is distributed worldwide with endemic species on every continent. It is represented in Australia and New Zealand by 19 and seven native species, respectively. In the present study we used a nuclear ribosomal internal transcribed spacer (ITS) phylogeny in comparison with a cpDNA phylogeny to unravel the origin of Australian/New Zealand species. Although phylogenetic relationships within Lepidium s.s. were not fully resolved, the cpDNA data were in agreement with a Californian origin of Lepidium species from Australia/New Zealand. Strongly conflicting signals between the cp- and nuclear DNA phylogenetic analysis clearly indicated hybridogenous genomic constitution of Australian Lepidium s.s. species: All 18 studied Australian/New Zealand Lepidium s.s. species examined shared a Californian cpDNA type. While eleven Australian/New Zealand species appeared to harbor a Californian ITS type, a group of seven species shared a South African ITS type. This pattern is most likely explained by two trans-oceanic dispersals of Lepidium from California and Africa to Australia/New Zealand and subsequent hybridization followed by homogenization of the ribosomal DNA either to the Californian or South African ITS type in the two different lineages. Calibration of our molecular trees indicates a Pliocene/Pleistocene origin of Lepidium in Australia/New Zealand. Low levels of cpDNA and ITS sequence divergence and unresolved topologies within Australian/New Zealand species suggest a rapid and recent radiation of Lepidium after the hybridization event. This coincides with dramatic climatic changes in that geological epoch shaping the composition of the vegetation.     

The vegetation of roadside verges with respect to environmental gradients in southern New Zealand

Abstract. A survey of the vegetation of roadside verges was made across the southern part of the South Island of New Zealand. Samples were taken at 10-km intervals along selected roads providing a climatic range from the suboceanic conditions of the east coast into semi-arid Central Otago, and from Central Otago through the Southern Alps to the hyper-oceanic areas of high rainfall on the west Coast. The variation in the floristic composition is associated mainly with variation in rainfall, continentality, altitude, soil acidity, soil organic matter, and presence of forest. Sites in the arable and pastoral regions on the eastern side of the Southern Alps support a herbaceous vegetation consisting mostly of exotic species of European origin, with a few native grasses scattered through the drier and less fertile sites. A greater proportion of native species is found at higher altitudes. Roadside vegetation in the area of high rainfall to the west is characterized by indigenous ferns and woody species, although vegetation adjacent to cleared areas is more similar to that on roadsides adjacent to farmland on the east coast. The pattern of distribution of both native and exotic species is strongly related to altitudinal and climatic gradients, and the environmental responses of the exotic species are similar to those recorded in Europe. This suggests a colonization of all available sites by the exotic species, despite the relatively short time since their introduction to New Zealand, rather than an incomplete invasion.     

Patterns of diversity and habitat relationships in terrestrial mollusc communities of the Pukeamaru Ecological District, northeastern New Zealand

Aim The New Zealand terrestrial mollusc fauna is among the most speciose in the world, with often remarkably high richness at lowland forest sites. We sought to elucidate general explanations for patterns of richness in terrestrial mollusc communities by analysis of species coexistence and habitat relationships within a New Zealand district fauna. Location Pukeamaru Ecological District, eastern North Island, New Zealand. Methods We sampled molluscs using qualitative methods at twenty-three sites and quantitatively by frame sampling of scrubland-forest floor litter at sixteen of these sites and analysed patterns of species richness and turnover in relation to regional species pools and local habitat attributes. We then tested for nonrandom assemblage of taxa along diversity and habitat gradients. Results Ninety-four indigenous mollusc species were recorded from a district fauna estimated at 102 indigenous species: only two species were endemic. From the presumptive geological history of the district, the low endemism, and Brooks parsimony and indicator species analyses of faunal relationships, the communities were indicated to have resulted by accumulation of colonists from other New Zealand districts since the Miocene. Richness ranged from two or three indigenous species in dune habitats to fifty-nine species in a floristically rich forest. Beta diversity was high and site occupancy per species was low, indicating communities structured by successive replacement of ecological equivalents. Sites differing in vegetation had characteristic species assemblages, indicating a degree of habitat specialization. Canonical correspondence analysis indicated that canopy tree species, canopy height, floristic diversity, altitude, litter mass, and litter pH were important determinants of species assemblage in scrubland and forest. Richness was strongly associated with site floristic diversity and, for litter-dwelling species, the pH of litter substrate. High richness occurred at those sites supporting molluscs in high abundance. Shell-shape distributions were essentially Cainian unimodal, with communities dominated by snail species with subglobose to discoidal shells. Mean and variance of shell size increased with mollusc species richness and floristic diversity at sites, indicating dominance of communities by small-shelled species at early successional or floristically poor sites, and increased richness resulting from addition of larger snails into vacant niches. Shifts in shell form were associated with sympatry in several congeneric taxa. Main conclusions The underdispersion of shell shape, relative to faunas elsewhere in the world, indicates that community structure in New Zealand land snail faunas has been constrained by limited phylogenetic diversity and/or by convergence upon successful adaptations. The remarkably high richness that characterizes these communities indicates special conditions allow coexistence of numerous species. The relationship between floristic diversity at sites and the richness, diversity, and shell-size distributions of the molluscs suggests assemblages structured around niche partitioning among competing species. While there is an element of congruence between vegetation and mollusc pattern, this study indicates that assembly rules will be defined, and spatial pattern predicted, only through a better understanding of the linkage between regional species pool, organism traits, environment, and local community assemblage.