In the “Protecting and restoring our natural heritage - a practical guide

This section outlines the main ecosystems you are likely to encounter and the main actions needed to manage them. Many will only be remnants.


Caution

Weed control is critical in all remnant ecosystems.

See Appendix 1 for key invasive weeds.


Forests and shrublands

Remnant forests and shrublands are often threatened by animal pests, weeds, stock, wind exposure, reduced water supply and physical isolation from similar ecosystems. Management will enhance natural processes such as plant regeneration and succession, reduce wind damage to forests and reduce predation of birds, lizards and invertebrates (e.g. insects, spiders and worms). Successful management will reduce the need for further intervention.

Shrublands are usually a temporary stage in the natural succession to forests, though in harsh environments they may be semi-permanent, e.g., kānuka woodlands in Central Otago, or saltmarsh ribbonwood/mākaka on estuarine margins. Shrublands support many native plants and animals and help buffer other ecosystems. They sometimes provide specialised habitat for threatened plants and animals. Where they do so, it may be appropriate to prevent native shrubland from developing to forest. You will need to seek specialist advice on this as management guidelines are still developing.

Key management actions

  • Prevent fires.
  • Control animal pests (rabbit control will be essential in dry shrublands).
  • Exclude stock by fencing.
  • Retain gorse and broom as a nurse crop, in some circumstances (see below).
  • Control other weeds, especially around edges or in open patches.
  • Undertake restoration planting around edges, in open areas or to provide linkages if needed (see sections 5 to 10).

Managing succession through shrub weeds

Shrubland and forest will succeed gorse, broom and other shrub weeds if certain conditions are met. The following material is summarised from McCracken 1993, and applies to eastern South Island conditions.

Native forest can develop through undisturbed gorse, broom and elderberry by natural succession in 10-20 years, though dry sites distant from seed sources will take longer. The shrub weeds initially form a dense canopy that suppresses grasses and weeds, and later protects seedlings and saplings of native plants. This process is a realistic option for marginal grazing land. Little intervention is needed if you follow a “minimum interference management” regime:

  • Exclude all domestic and wild animals by fencing or other means.
  • Prevent fire, as broom and gorse will prosper most.
  • Clear all property boundaries of gorse and broom for a width of at least 10 m, to meet statutory requirements.

Table 3. Factors affecting succession through gorse and broom.

Key Factors Score
Rainfall > 1200 mm (wet) 5
700 -1200 mm (moderate) 3
< 700 mm (dry) 1
Aspect/exposure E/S/W (cool, moist) 5
NW/N/NE (dry, warm) 1
Distance from
native seed source
< 2 km (close) 5
2 - 10 km (moderate) 3
> 10 km (distant) 1
Total score of 11-15: [moist sites close to seed sources] - high potential for quick succession, with no enrichment planting needed.

Total score of 6 - 10: - good potential for succession; enrichment planting may be needed, but only after the natural process has been given a reasonable trial.

Total score of 3-5: - succession will occur only if seed sources are a moderate distance away, and will be dependent on favourable seasons; enrichment planting may be needed.

The lower the score, the more important it is that grazing or browsing is prevented. The density of gorse and broom affects the rate of succession – as dense stands age, they become more open and move more quickly to succession, especially in the absence of grazing or browsing.

Near the upper natural limit of native trees, you should control all new outbreaks of broom or gorse. This is important, as there may be no remaining native trees to suppress them here. Controlled grazing may provide a holding measure. If a native seed source is nearby, trees like beech/tawai, mountain tōtara and mountain celery pine/toatoa may eventually overtop the shrub weeds.

Grasslands and herbfields

Grassland and herbfield communities feature turf grasses, tussocks or broad-leaved herbs. Because many grasslands have been induced by the destruction of forests and shrublands, there is likely to be a natural trend of succession back to woody vegetation. Induced grasslands often support native plants and animals that may not be present or abundant elsewhere. As a result, it may sometimes be appropriate to prevent natural succession to shrubland or forest, e.g., to maintain populations of uncommon species or to retain a tussock landscape.

Management aims to control exotic grasses and weeds, and encourage natural processes. Wilding trees can be a serious problem, especially in mountain grasslands. You should not use fertiliser where many small native plants grow amongst the tussocks, as it favours exotic species. Managing short tussock grasslands is particularly difficult because of widespread exotic grasses and hawkweeds (Hieracium spp.). Tall tussock grasslands are less problematic if they are sufficiently dense to shade out exotic grasses and weeds, particularly hawkweeds. Burning to retain tall tussock is problematic, as it favours the spread of weeds and may contribute to soil nutrient losses. Controlled grazing can be used as a management tool, and may help browse-resistant, woody nurse plants like kānuka, to colonise exotic pasture.

Because of the complexities of grassland management, you should seek further information and specialist advice.

Key management actions

  • Graze short tussocklands if competition from ungrazed exotic grasses is a problem, e.g., on fertile soils.
  • Exclude stock from mountain and degraded grasslands, or graze infrequently if exotic grasses are only a minor problem.
  • Control wilding trees by removing, and painting the stumps with herbicide if necessary.
  • Exclude stock from dense or regenerating tall tussocklands (say >20% cover).
  • Control rabbits in dry to moderate rainfall areas.
  • Exclude oversowing and topdressing, unless a tussock appearance is the main purpose.
  • Prevent fires, but seek specialist advice if trying to maintain tall tussockland.

Wetlands and riparian areas

Wetlands are permanently or intermittently wet areas characterised by peaty or grey soils, and plants and animals adapted to these conditions. Open water may be absent or only periodically present. Wetlands include coastal lagoons and estuaries, which support plants and animals tolerant of saline or brackish conditions. They provide an essential link between marine and freshwater ecosystems and are vital to the life cycle of many fish, birds and invertebrates. Riparian areas occur alongside waterways and water bodies; they provide valuable habitat for plants and animals, and affect water quality. Wetlands and riparian areas are often degraded by human use. Grazing affects most unprotected wetlands and riparian areas, reducing vegetation stature and density and letting in more light. This makes them vulnerable to drying out and invasion by weeds.

The single most important factor in protecting a wetland is sustaining its water supply. Other management actions aim to exclude stock, reduce weeds, prevent substrate damage and reduce nutrient inputs. You may need to control vehicle use as it can damage faunal habitat, vegetation and substrates. Nesting birds are disturbed by motorboats, which may need to be controlled. If you wish to maintain a mosaic of open water and emergent vegetation, you may need to control raupō as it colonises open water. As a result of management, moisture levels and plant regeneration should increase. It is important to recognise that wetlands tend to dry out through natural processes and be colonised by woody vegetation. For this reason and their inherent complexity, you should seek specialist advice about their management, e.g., grazing to maintain turf communities or bird habitat.

A profile of mature riparian/lakeshore vegetation.
A profile of mature riparian/lakeshore vegetation

 

 

 

 

 

 

 

 

 

 

 
 

If you protect and restore riparian areas, water quality should improve, flood peaks decline and habitat for land and water animals increase. A minimum riparian width of 10 m is recommended on either side of a stream, but you will need larger buffers for rivers, i.e., 20 m plus. The width of a protected riparian area most likely to support self-sustaining native vegetation with minimal maintenance, is 15-20 m (NIWA 2000).

Key management actions

  • Improve water supply if necessary, e.g., by blocking or redirecting a drain.
  • Exclude stock except in special circumstances.
  • Exclude oversowing and topdressing to reduce nutrient input and grazing.
  • Control weeds.
  • Prevent fires.
  • Control animal pests.
  • Control human impacts, e.g., motorboat and off-road vehicle use.
  • Undertake restoration planting if needed.

Coastal dunelands and banks

Dunelands close to settlements and farmland are more vulnerable to a range of uses. On these dunelands, historic burning and grazing triggered erosion. The marram grass, tree lupin and pines planted to stabilise the sand then displaced native species such as pïngao and spinifex/kōwhangatara. Native dune vegetation is now less common, and natural dune and bank systems are usually found only in remote locations.

Management aims to reduce vegetation damage from animal pests, stock, weed competition and human over-use. Protection also increases natural plant regeneration and succession, and limits disturbance and predation of native animals, particularly lizards. You may need to undertake restoration planting of communities where native dune-binding plants (spinifex/kōwhangatara, pïngao and sand tussock) have disappeared or are only sparse. This may include blowout sites. You may also need to plant coastal bush and shrubland on reardunes to help remedy their past destruction.

You can fertilise existing depleted stands of foredune sand-binders to boost growth and cover without significantly increasing weed growth. This is far cheaper than planting programmes (D Bergin, pers. comm.). You should only fertilise where plants are not vigorous and where you want vegetation cover to spread onto bare sand. Use only small amounts of broadcast fertiliser, say 50 kg N/ha, 2-3 times a year, as other environmental effects such as those on invertebrates and microbes are unknown (D Bergin, pers. comm.). You should monitor plant responses and stop fertiliser additions once plant cover or vigour increases.

Key management actions

  • Exclude stock.
  • Control weeds.
  • Exclude vehicle use, including motorbikes and off-road vehicles.
  • Limit walking access across dunes if necessary.
  • Control animal pests.
  • Prevent fires.
  • Replant lost communities.

Further reading

Bowenvale vegetation, assessment and management recommendations. Meurk CD and Wilson HD 1990. [Booklet – a short report that includes discussion of the grazing of short tussock grasslands, plant succession and nurse plants]

Canterbury region wetlands. Preliminary report and inventory. Davis M 1999. [Book, available from Environment Canterbury – includes general discussions of wetland functioning, threats and restoration needs]

Christchurch waterway maintenance plant guide. Weeds, and how to tell them from similar looking plants. McCombs K, Meurk C and Morland K 1999. [Book - available on request from Christchurch City Council – contains clear photographs and descriptions for easy plant identification]

Coastal sand dunes, form and function. Hesp PA 2000. [Booklet – describes the different types of dunes, their functioning and dynamics, erosions issues and the importance of coastal dunes]

Managing riparian zones: a contribution to protecting New Zealand’s rivers and streams. Collier KJ, Cooper AB, Davies-Colley RJ, Rutherford JC, Smith CM and Williamson RB 1995. [Two books – volume 1 outlines why riparian zones areimportant, and the natural processes affecting rivers and streams; volume 2 provides guidelines for specific problems like bank instability, grazing and increasing habitat diversity. Note – for ecological restoration, we recommend the use of cabbage trees, NZ flax, toetoe, kōhūhu (Pittosporum tenuifolium), karamū (Coprosma robusta) and lowland ribbonwood for erosion control, rather than exotic trees]

Managing waterways on farms: a guide to sustainable water and riparian management in rural New Zealand (draft). Ministry for the Environment 2000. [Book – outlines what a healthy waterway is, the impacts of agriculture and forestry, managing problems and restoring riparian vegetation; includes 16 case studies. Note – for ecological restoration, we recommend the use of cabbage trees, NZ flax, toetoe, kōhūhu (Pittosporum tenuifolium), karamū (Coprosma robusta) and lowland ribbonwood for erosion control, rather than exotic trees]

Native forest restoration. A practical guide for landowners. Porteous T 1993. [Book – comprehensive coverage of managing remnants, with detailed restoration techniques]

New Zealand’s wetlands. A management guide. Buxton R 1991. [Book – describes different types of wetlands and their functioning, and provides management and restoration guidelines and summaries]

Rehabilitation of coastal foredunes in New Zealand using native sand-binding species. Bergin DO and Kimberley MO 1999. [Book, available from DOC Science Publications – covers pïngao, sand tussock and spinifex, which are separately addressed in other references by Bergin]

Review of information on riparian buffer widths necessary to support sustainable vegetation and meet aquatic functions. National Institute of Water and Atmospheric Research 2000. [Book – site visits were made and native vegetation was considered to be more sustainable over the long term than exotic vegetation]

Riparian zones. A guide to the protection of Canterbury’s rivers, streams and wetlands. Canterbury Regional Council (undated3). [Pamphlet - available from Environment Canterbury – outlines erosion control, habitat values, pollution control and riparian planting. Note – for ecological restoration, we recommend the use of cabbage trees, NZ flax, toetoe, kōhūhu (Pittosporum tenuifolium), karamū (Coprosma robusta) and lowland ribbonwood for erosion control, rather than exotic trees]

The natural succession option. A strategy to replace gorse and broom on Canterbury’s marginal pastoral lands with native forest. Canterbury Regional Council (undated2). [Pamphlet, available from Environment Canterbury – outlines natural succession by native woody species, and factors affecting succession potential. It is based on the booklet by McCracken 1993, which is straightforward and provides more detail]

Wetland plants in New Zealand. Johnson PN and Brooke PA 1989. [Book – a detailed plant identification text, with a discussion of wetland habitats and vegetation]

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