Key words: Lowland temperate forest, animal pest control, weed control, restoration plantings, public access, cultural values, farmland restoration
Introduction. Commencing in 2004, the 407 ha Tiromoana Bush restoration project arose as part of the mitigation for the establishment of the Canterbury Regional Landfill at Kate Valley, New Zealand. The site lies one hour’s drive north of Christchurch City in North Canterbury coastal hill country (Motunau Ecological District, 43° 06’ S, 172° 51’ E, 0 – 360 m a.s.l.) and is located on a former sheep and beef farm.
Soils are derived from tertiary limestones and mudstones and the site experiences an annual rainfall of 920mm, largely falling in winter. The current vegetation is a mix of Kānuka (Kunzea robusta) and mixed-species shrubland and low forest, restoration plantings, wetlands, Gorse (Ulex europaeus) and European Broom (Cytisus scoparius) shrubland and abandoned pasture. Historically the area would have been forest, which was likely cleared 500-700 years ago as a result of early Māori settlement fires. A total of 177 native vascular plant and 22 native bird species have been recorded, including four nationally threatened species and several regionally rare species.
Before and after photo pair (2005-2018). showing extensive infilling of native woody vegetation on hill slopes opposite, restoration plantings in the central valley, and successional change from small-leaved shrubs to canopy forming trees in the left foreground. (Photos David Norton.)
Project aims. The long-term vision for this project sees Tiromoana Bush, in 300 years, restored to a: “Predominantly forest ecosystem (including coastal broadleaved, mixed podocarp-broadleaved and black beech forests) where dynamic natural processes occur with minimal human intervention, where the plants and animals typical of the Motunau Ecological District persist without threat of extinction, and where people visit for recreation and to appreciate the restored natural environment.”
Thirty-five year outcomes have been identified that, if achieved, will indicate that restoration is proceeding towards the vision – these are:
- Vigorous regeneration is occurring within the existing areas of shrubland and forest sufficient to ensure that natural successional processes are leading towards the development of mature lowland forest.
- The existing Korimako (Bellbird Anthornis melanura) population has expanded and Kereru (Native Pigeon Hemiphaga novaeseelandiae) are now residing within the area, and the species richness and abundance of native water birds have been enhanced.
- The area of Black Beech (Fuscospora solandri) forest has increased with at least one additional Black Beech population established.
- Restoration plantings and natural regeneration have enhanced connectivity between existing forest patches.
- Restoration plantings have re-established locally rare vegetation types.
- The area is being actively used for recreational, educational and scientific purposes.
Day-to-day management is guided by a five-year management plan and annual work plans. The management plan provides an overview of the approach that is being taken to restoration, while annual work plans provide detail on the specific management actions that will be undertaken to implement the management plan.
Forest restoration plantings connecting two areas of regenerating Kānuka forest. Photo David Norton.
Restoration approach and outcomes to date. The main management actions taken and outcomes achieved have included:
- An Open Space Covenant was gazetted on the title of the property in July 2006 through the QEII National Trust, providing in-perpetuity protection of the site irrespective of future ownership.
- Browsing by cattle and sheep was excluded at the outset of the project through upgrading existing fences and construction of new fences. A 16 km deer fence has been built which together with intensive animal control work by ground-based hunters has eradicated Red Deer (Cervus elaphus) and helped reduce damage caused by feral pigs (Sus scrofa domesticus).
- Strategic restoration plantings have been undertaken annually to increase the area of native woody and wetland vegetation, as well as providing food and nesting resources for native birds. A key focus of these has been on enhancing linkages between existing areas of regenerating forest and re-establishing rare ecosystem types (e.g. wetland and coastal forest).
- Annual weed control is undertaken focusing on species that are likely to alter successional development (e.g. wilding conifers, mainly Pinus radiata, and willows Salix cinerea and fragilis) or that have the potential to smother native regeneration (e.g. Old Man’s Beard Clematis vitalba). Gorse and European Broom are not controlled as they act as a nurse for native forest regeneration and the cost and collateral damage associated with their control will outweigh biodiversity benefits.
- Establishment of a public walking track was undertaken early in the project and in 2017/2018 this was enhanced and extended, with new interpretation included. Public access has been seen as a core component of the project from the outset so the public can enjoy the restoration project and access a section of the coastline that is otherwise relatively inaccessible.
- Part of the walkway upgrade included working closely with the local Māori tribe, Ngāi Tūāhuriri, who have mana whenua (customary ownership) over the area. They were commissioned to produce a pou whenua (land marker) at the walkway’s coastal lookout. The carvings on the pou reflect cultural values and relate to the importance of the area to Ngāi Tūāhuriri and especially values associated with mahinga kai (the resources that come from the area).
- Regular monitoring has included birds, vegetation and landscape, with additional one-off assessments of invertebrates and animal pests. Tiromoana Bush has been used as the basis for several undergraduate and postgraduate student research projects from the two local universities.
Vigorous regeneration of Mahoe under the Kānuka canopy following exclusion of grazing animals. Photo David Norton.
Lessons learned. Important lessons learned over the 15-years have both shaped the approach to management at this site and have implications for the management of other projects:
- Control of browsing mammals, both domestic and feral, has been essential to the success of this project. While domestic livestock were excluded at the outset of the project, feral Red Deer and pigs have the potential to seriously compromise restoration outcomes and these species have required additional management inputs (fencing and culling).
- Since removal of grazing, the dominant exotic pasture grasses, especially Cocksfoot (Dactylis gomerata), now form tall dense swards. These swards severely restrict the ability of native woody plants to establish and herbicide control is used both pre- and post-planting to overcome this. During dry summers (which are common) the grass sward is also a significant fuel source and the walkway is closed during periods of high fire risk to avoid accidental fires which would decimate the restoration project.
- Regular monitoring is important for assessing the biodiversity response to management. Annual photo-monitoring now spanning 15-years is highlighting significant changes in land cover across the site, while more detailed monitoring of plants and birds is strongly informing management actions. For example, seven-years of bird monitoring has indicated an ongoing decline in some native birds that is most likely due to predation (by cats, mustelids, rodents, hedgehogs). As a result, a predator control programme is commencing in 2019.
- Simply removing grazing pressure from areas of existing regenerating native woody vegetation cannot be expected to result in the return of the pre-human forest because of the absence of seed sources. Permanent plots suggest that Kānuka is likely to be replaced by Mahoe (Melicytus ramiflorus), with few other tree species present. Gap creation and enrichment planting is therefore being used to speed up the development of a more diverse podocarp-angiosperm forest canopy.
Kate Pond on the Tiromoana Bush walkway. The pond and surrounding wetland provides habitat for several native water birds. Photo Jo Stilwell.
The pou whenua on the coastal lookout platform looking north up the coastline. Photo David Norton.
Looking to the future. Considerable progress in restoring native biodiversity at Tiromoana Bush has been achieved over the last 15 years and it seems likely that the project will continue to move towards achieving its 35-year outcomes and eventually realising the long-term vision. To help guide management, the following goals have been proposed for the next ten-years and their achievement would further help guarantee the success of this project:
- The main valley floor is dominated by regenerating Kahikatea (Dacrycarpus dacrydioides) forest and wetland, and the lower valley is dominated by regenerating coastal vegetation.
- At least one locally extinct native bird species has been reintroduced.
- Tiromoana Bush is managed as part of a wider Motunau conservation project.
- The restoration project is used regularly as a key educational resource by local schools.
- The walkway is regarded as an outstanding recreational experience and marketed by others as such.
- Tiromoana Bush is highly valued by Ngāi Tūāhuriri.
Kereru, one of the native birds that restoration aims to help increase in abundance. Photo David Norton.
Stakeholders and funding. The project is funded by Transwaste Canterbury Ltd., a public-private partnership company who own the landfill and have been active in their public support for the restoration project and in promoting a broader conservation initiative in the wider area. Shareholders of the partnership company are Waste Management NZ Ltd, Christchurch City Council and Waimakariri, Hurunui, Selwyn and Ashburton District Councils.
Contact Information. Professor David Norton, Project Coordinator, School of Forestry, University of Canterbury, Private Bag 4800, Christchurch 8140, New Zealand. Phone +64 (027) 201-7794. Email email@example.com