Highlights: Biodiversity
Rowan Buxton & Richard Clayton sampling dryland biodiversity
Trends in national and regional biodiversity on public and private land are understood and based on best available descriptions for species and comprehensive indices of ecological integrity.
Impact 1
Understanding ecosystem retrogression
Chronosequences (a locality where soils span a sequence of ages) provide valuable insights into ecosystem development over thousands to millions of years. An international project team, led by Landcare Research, reviewed and synthesised research from across many disciplines to better understand the causes and ecological consequences of retrogression. The review revealed that there are predictable, coordinated shifts in vegetation and soil communities and ecological processes during both ecosystem progression and retrogression, with phosphorus more important in the long term than nitrogen. Similar patterns of retrogression occur in areas with vastly different climatic regimes, geologic substrates, and vegetation types, even though the timescales and mechanisms driving retrogression may vary greatly among sites. Studies on retrogression also provide evidence that, in many regions, high biomass or ‘climax’ forests are often transient, and do not persist indefinitely in the absence of rejuvenating disturbance.
The review was selected as a ‘must read’ by the Faculty of 1000 Biology: ‘This review brings new clarity to the overall scheme of ecosystem development over long time periods, sheds new light on the importance that phosphorus has played in shaping the Earth’s ecosystems, and unifies previously disparate analyses of ecosystem retrogression.’
Comprehensive new classification system for forest and shrubland
More than 70% of New Zealand’s forest and shrubland has been lost in the 800 years since human arrival, through fire, land clearance and logging. Remaining forest and shrubland continues to be modified and lost (through, for example, invasive species and land–use change), so an upto–date depiction of the composition, extent and structure of these woody communities at a range of scales is urgently needed. Researchers used the LUCAS (New Zealand Land Use and Carbon Analysis System) network (1177 vegetation plots positioned on an 8 km x 8 km grid across the country) to identify 24 different broad vegetation classes, termed ‘alliances’. Each alliance was evident in 19–105 plots, with each comprising an estimated land area of 144,000– 794,000 ha. Stand structure data suggest that 16 of these alliances are largely stable whereas eight will undergo compositional change; the new classification system will be invaluable in managing that change.
Previous classifications and vegetation maps were either out of date, too broad, or didn’t accurately depict the actual vegetation. The new classification also highlights the extent of disturbed landscapes where alliances are compositionally dynamic, and being invaded by exotic species. These are areas with high potential for future carbon sequestration and biodiversity enhancement, but which are poorly understood.
Naturally uncommon ecosystems
‘Naturally uncommon ecosystems’ are included in the Ministry for the Environment (MfE)’s priorities in developing the National Policy Statement on Biodiversity. We were commissioned by MfE to determine the level of spatial overlap between naturally uncommon ecosystems and LENZ threatened environments, which are also one of the national priorities. The wide range of overlap between the two classi?cation systems provided a good example of how the proposed statement uses complementary criteria to identify areas of potential biodiversity value.
Different types of naturally uncommon ecosystems cover total areas ranging from less than 100 ha to more than 10,000 ha, with protection status varying from none (almost solely on private land) to extensive (mostly on public conservation land). It is imperative that overall intactness and the condition of each naturally uncommon ecosystem is assessed to indicate threat status, which is critical for policy implementation.
Regional councils’ biodiversity monitoring framework
Following our work with the Department of Conservation (DOC) to develop a national biodiversity monitoring and reporting framework, adopted by DOC in June 2010, we have been working with regional councils to agree on a suite of indicators for a regional–scale monitoring of the condition and trend in terrestrial biodiversity.
Over the next two years, we will begin developing the tools that enable all regional councils in New Zealand to report consistently on terrestrial biodiversity, contributing to a more scientifically sound and informative picture at the regional scale, with data integrated more readily with DOC’s work at the national scale and State of the Environment reporting by MfE. The framework will assist councils to assess the effectiveness of different policy and regulatory approaches, decide where to allocate limited resources and provide greater accountability for rates expenditure, and make improvements to the protection of indigenous biodiversity.
Biodiversity of dryland environments
Dryland environments contain some of the most transformed, least protected and most threatened native ecosystems and species in New Zealand; only 3% is legally protected. Protection versus land use intensification is hotly debated and long–term monitoring studies provide important evidence for policy decisions.
The 1000 ha of dryland tussock grassland in the Tekapo Scientific Reserve is the only sizeable place where stock
12 have been absent and rabbits and wilding pines controlled to low levels for nearly 20 years. When it was destocked in 1992, the land was highly degraded and denuded, being dominated by bare ground and mouse–ear hawkweed (Hieracium). Permanent grassland plots established a monitoring baseline against which changes could be compared. This year with DOC, we resampled these plots plus some additional areas. After 18 protected years, the resurgence of tussocks and other palatable native species, including several rare and uncommon species, has been astonishing.
Further evidence that removing grazing benefits dryland biodiversity is coming from studies on land retired from pastoral use through Tenure Review. Sites that are still grazed were compared with equivalent sites where grazing ceased 10–30 years ago. Ungrazed sites had significantly greater native vegetation richness and fewer exotic species, more native shrubs and taller shrub cover than was found at the grazed sites.
Research supports increased legal protection of these important environments before widespread land–use intensification and irrigation cause irreversible changes.
Tūī returning to Hamilton
Recently completed biennial bird counts in Hamilton showed a three–fold increase in the incidence of tūī visiting the city compared with two years ago. This confirms the effectiveness of peri–urban pest control, which is mostly undertaken by Environment Waikato based on Landcare Research advice. A decade of research showed tūī mainly visited urban and rural areas in the winter. They nested in native forest remnants on the fringes of the Waikato Basin but their nesting success was poor; ship rats and possums were the main cause of nesting failure. Intensive control of ship rats and possums has clearly increased tūī abundance in the wider Waikato, including Hamilton City.
Impact 2 The most threatened ecosystems, habitats and species can be managed to reduce the risk of decline in native biodiversity.
Mokihinui Restoration Project
The Mokihinui Restoration Project (MRP) is a large–scale, long–term ecological restoration project initiated by Solid Energy and DOC to see if extensive wild animal control produces detectable gains in carbon stocks. The MRP will cover 18,600 ha of native forest and other natural vegetation in the North Branch of the Mokihinui River, North Westland. At Solid Energy’s request, we reviewed the project design with Resource Consultants Ltd. We identified a number of significant weaknesses. To remedy these inadequacies, we provided Solid Energy with a scientifically robust monitoring framework that is (1) capable of detecting reasonable changes in carbon sequestration within the project area, and (2) able to demonstrate the magnitude of any ‘additional’ gains attributable directly to the management intervention. We recommended that further plots were established to monitor potential changes in areas of regenerating vegetation not currently sampled. To enable the separation of carbon gains due to wild animal control from background changes in carbon, we recommended they establish appropriate experimental control ‘non–treatment’ plots, and analyse existing datasets (e.g. LUCAS) where appropriate.
The MRP project is internationally novel and contributes to New Zealand’s obligations to conserve and enhance carbon sinks under the United Nations Framework Convention on Climate Change. This ongoing project is an excellent opportunity to investigate the potential for private–industry–funded animal (ungulate) control to result in carbon sequestration as well as biodiversity gains on public conservation land.
Possum control reduces tree mortality
Introduced possums are one of the most significant pests in New Zealand’s indigenous forest but how much and how quickly forests respond to possum control is (surprisingly) not well understood. Between 1996 and 2004, researchers measured the increase of possum populations after aerial 1080 poisoning, and how possum–preferred tree species responded to those changes. Possum densities, much reduced after poisoning, usually recovered quickly to near pre–control levels within six years. The overall mortality of possum–preferred tree species was about 25% lower at poisoned sites compared with unpoisoned sites, although this varied between species. Canopy condition of some of the most common and widespread species such as kāmahi, māhoe and tawa continued to recover even when possum numbers had substantially recovered. The results initially suggested that reducing possum density by 60% (modest by today’s standards) would protect most possum–preferred trees, but more detailed analysis of kāmahi mortality indicated that some individuals in some areas would remain vulnerable.
Biocontrol of tradescantia
Tradescantia is a serious environmental weed throughout much of New Zealand and other countries. The first releases of the tradescantia leaf beetle as a biocontrol agent, a global first, were made in the Auckland Region earlier this year; with further releases in Northland, Bay of Plenty, Waikato and Manawatu–Wanganui. The releases follow an intensive 2–year programme to rid the rearing colony of a gregarine gut parasite. This project is collaborative with DOC and the National Biocontrol Collective (including the Auckland Council).
The Environmental Protection Agency (formerly ERMA) also approved the release of two additional agents for tradescantia (the tip beetle and stem beetle).
Joint management of traditional land
A number of settlements and claims under the Treaty of Waitangi represent major changes in land tenure and natural resource management in New Zealand. Landcare Research is working with several iwi on options for conservation land management and governance.
A study tour to Australia’s Northern Territory (with participants from Tūhoe, Ngātiwai, Ngā Puhi, Avonside Girls High School and CSIRO) examined joint management models on traditional–owner lands. Specific areas of interest included understanding the leasing, governance, and management structures used; and evaluating the benefits accruing to traditional owners from joint management. It was clear that, over a number of decades, some joint management models are achieving some goals (e.g. protecting areas) but fall short on others (e.g. employment of traditional owners).
The similar study tour to Canada involved Landcare Research, University of Canterbury and Te Kotahi a Tūhoe. The group met with the Kativik Regional Government (a non–ethnic regional government that supports both Inuit and non–Inuit aspirations) and the Nunavik Land Holding Corporation. This visit provided a useful contrast to the Australian situation.
The challenge is to draw from these overseas models to develop local capacity and conservation management approaches that fulfil iwi aspirations.