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Introduction
Response: The primary response to dealing with soil moisture deficits and frost in the restoration plantings is to only use plants adapted to conditions in Tiromoana Bush, including sourcing all plant material locally. Additionally, plants will be hardened off before planting, planting will be timed to occur so that plants are well established before summer droughts but are not planted until after the worst of winter frosts, herbicide will be used to kill the grass sward before planting, and hand weeding and mulches will be used after planting as required to reduce competition for water.
Constraint: Because of the frequent occurrence of long dry periods during summer, and the presence of gorse shrubland which burns readily, a wildfire could rapidly sweep through Tiromoana Bush destroying restoration plantings and natural regeneration.
Response: Ensuring that no burn-offs occur elsewhere on Transwaste Canterbury Ltd. land, liaising with adjacent landowners about the threat of burn-offs to restoration, informing the public of the fire danger through appropriate signs and other means, enforcing a total open fire ban in Tiromoana Bush, and maintaining water reservoirs for fire fighting purposes.
Constraint: Because adjacent land uses include pastoral farming and forestry, weed spraying in adjacent areas has the potential to damage natural regeneration and restoration plantings if drift occurs.
Response: Liaising with adjacent landowners about the threat of spray-drift to restoration, and ensuring that any spraying undertaken on Transwaste Canterbury Ltd. land (e.g., associated with plantation forestry or the landfill) does not impact on the restoration area.
Response: All domestic stock will be removed from Tiromoana Bush at the start of the restoration project and fences will be regularly inspected to ensure that they do not gain entry in the future. Should domestic stock be found in the restoration area, they will be quickly removed.
Constraint: One of the major factors likely to limit restoration success, including restoration through natural regeneration, is browsing and predation by introduced animals, especially possums, deer, goats, rabbits, hares, stoats, ferrets, rats and mice. Browsing reduces viability and growth rates of plants, while the impact of predation on invertebrate, reptile and bird species influences restoration success as these species play key roles in ecosystem processes such as pollination, seed dispersal and nutrient cycling.
Response: An ongoing and comprehensive animal pest control programme will be undertaken within Tiromoana Bush. In addition extensive animal pest control will be undertaken in association with management of the adjacent landfill.
Constraint: Introduced plant species have the potential to severely limit the restoration success. A number of grasses are highly competitive (e.g., browntop and cocksfoot) and can lead to the loss and poor health of plantings. There is considerable potential for invasive woody species already present, or present in adjacent areas to expand their range and dominate large parts of Tiromoana Bush.
Response: Grasses will be sprayed prior to establishing restoration plantings, while some hand weeding together with mulches will be used to reduce subsequent grass growth as required. Regular surveys and control operations will be undertaken for other identified problem weeds, especially woody weeds, with the aim of eradicating those species identified as a management priority.
Constraint: Planting of non-local plant material may result in loss of local adaptations (e.g., to particular environmental conditions) and eventually could lead to a loss of overall genetic variation within particular species. It is therefore prudent to use plant material of local origin as local plants will be better adapted to local conditions than non-local plants (e.g., resistance to salt spray) and as a safe-guard for maintaining genetic diversity.
Response: To ensure that plants are adapted to local environmental conditions and to minimise the loss of genetic variability only locally sourced planting material will be used for the restoration plantings (preferably from within Tiromoana Bush or, when not available, from the coastal flanks of the southern part of the Motunau Ecological District).
Constraint: In using seed for propagation a key constraint for some species is year-to-year variation in seed production (called masting). Beech in particular is mast seeding, with years of heavy seed production separated by several years with little or no seed production.
Response: Where seed is to be used as the basis for plant propagation, consideration of mast years will be undertaken as part of propagation planning. In addition all efforts will be made to utilise plant material from Remnant “A” over the 10-year period before it is removed.
Constraint: The development of associations between planted species and various mycorrhizal fungi is important for restoration success as mycorrhizal fungi play a key role in nutrient uptake. An absence of mycorrhiza may be a limiting factor for some species including beech and kanuka.
Response: Where possible, nursery propagation of seedlings for restoration will include inoculation with forest organic matter sourced from Remnant “A” to ensure the presence of mycorrhiza (especially for beech and kanuka). In addition, coarse woody debris from Remnant “A” and forest organic matter will be collected prior to the removal of Remnant “A” and spread through areas of restoration plantings and regenerating forest to facilitate the spread of indigenous biodiversity and/or to provide habitat for indigenous species to utilise.
Constraint: A key premise of restoration is that management will speed up the natural processes of succession by establishing a cover of woody plants that will encourage the development of mature shrubland and forest. Some of the species that occur in these forests require birds for pollination and/or dispersal. However, severe predation pressure appears to have reduced bird numbers to levels that may be limiting these processes and hence have the potential to limit restoration success.
Response: Undertake predator control to reduce direct impacts on indigenous birds and use strategic planting of key food resources for these birds where food resources are considered to be insufficient.
Response: Tiromoana Bush will be covenanted through an appropriate organisation (e.g., QEII National Trust) to ensure that the tenure of the site as a conservation area is secured in perpetuity.
A number of factors are likely to limit the success of management in achieving both the 5- and 35-year restoration outcomes, and ultimately the long-term vision for the site. A clear recognition of these constraints is essential to ensure that restoration is implemented in a manner that addresses them all.
Constraint: Climate is likely to limit natural regeneration and restoration through low soil moisture availability and frost. Restoration plantings and natural regeneration into grassland are particularly vulnerable to soil moisture deficits, especially during the initial stages of establishment. Winter frost can be a major source of mortality for some species in restoration plantings, especially for species such as ngaio.
Constraint: Grazing by domestic stock (sheep and cattle) is a major limitation to natural regeneration, with most areas of regenerating forest and remnant forest having severely grazed understories. In addition, domestic stock can quickly destroy young restoration plantings if they gain access to these.
Constraint: The success of the Tiromoana Bush Restoration Project will not be realised for many years after the end of the life of the Kate Valley landfill. There is therefore potentially uncertainty over the long-term security of the restoration site beyond this time-frame.