Restoration strategy for the Te Kākahu Kahukura project

The following six key components for on-the-ground management need to be commenced in the short-term (five-years) to implement the Te Kākahu Kahukura project. All are obviously dependent on appropriate funding and landowner support, but it is important that they are all implemented because of inter-dependencies between them:

Establish baseline monitoring including a comprehensive photo-monitoring network, and site-based monitoring of birds and plants developing from existing CCC work but expanded to cover the whole area. This should focus on both existing areas of native vegetation (forest remnants and regenerating forest) and new areas that are being planted.

1. Implement an herbivore control programme across the area focusing on deer (red and fallow) and pigs (this is essential to allow other work to proceed and without adequate control, large scale plantings will be wasted).
2. Work with landowners to exclude degrading factors from the remaining remnants of native habitat (e.g. livestock and weeds like vines) – these sites are key sources for seed dispersal.
3. Targeted large-scale restoration to enhance connectivity between key areas of existing native habitat focusing on grassland areas.
4. Targeted enrichment planting of native regenerating forests with old-growth tree species that are now rare in the area (especially the conifers lowland and thin-barked tōtara, mataī, kahikatea and miro, and angiosperms such as titoki, kōwhai and pigeonwood).
5. Work with CCC and SDC to ensure that public access points along the Summit Road are managed in a manner, including through the use of low-flammability species in plantings (five-finger, broadleaf etc), to reduce the chances of fire ignition.

The following notes provide more detail on species composition and planting patterns for components 4 and 5 above.

Large-scale restoration

The basic approach suggested for large-scale restoration here is to established mixed species plantings similar to those established in the post-burn plantings, but with old growth canopy tree species interspersed through these. Species composition for the initial plantings should consider elevation and aspect, with also some consideration being given to the flammability of species in particular locations (especially adjacent to roads and tracks).

Our preference is to have a relatively broad mix of species planted, but tending to favour those species that do best in particular microsites (e.g. in terms of frost sensitivity or moisture stress). Existing restoration plantings are good indicators for species choice. A good mix of species provides resilience against adverse climatic events and a heterogeneous environment for establishment and growth of new species arriving in by bird and wind dispersal. A list of possible species in included in the table on the next page.

Within this mix, potential old-growth canopy species such as lowland tōtara, thin-bark tōtara, mataī, kahikatea, miro, tītoki, kōwhai and pigeonwood should be established in small groups of 4-5 individuals of the same species in favourable microsites (deeper soil and where possible more shelter from NW and NE winds). These old growth species could also be planted 4-5 years’ later when the initial plantings provide shelter. In that case, gaps should be left which could be planted with shrubs such as Banks Peninsula korimako or tutu. Densities for old growth tree clumps do not need to be high, perhaps spaced 50 m apart as their role is to speed up the succession to old-growth forest once the initial canopy has established and to act as seed sources for future establishment into the planted mix. The logic for including 4-5 individuals in each clump is to allow for potential mortality.

Suggested species for the main mix:

Enrichment plants

A range of native shrub and small tree species including māhoe, karamu, kōhūhū, five-finger etc are able to establish under seral nurse canopies including bracken and gorse. Where grazing pressure is controlled and seed sources are present, establishment of native forest species is also occurring under more mature native seral stands such as those dominated by kānuka. For example, in Kennedy’s Bush and Omahu Bush, tōtara seedlings can be found under 50+ year old kānuka where seed sources are present. However, this is not the case throughout all the Te Kākahu Kahukura Project area because seed sources of old-growth trees are limited and the transition from seral native forests to forests dominated by old-growth native tree species is likely to be slow.

It is therefore proposed that enrichment planting with old-growth native trees is undertaken across a range of seral stands, but focusing especially on those that have a reasonably well-developed native canopy (e.g. mixed-angiosperm or kānuka). Enrichment should involve the establishment of small single-species clusters of old growth trees (4-5 individuals of lowland or thin-bark tōtara, mataī, kahikatea, tītoki, kōwhai, pigeonwood etc) in either natural gaps or artificial gaps created in the existing canopy (see Forbes et al. 2020 for the scientific rationale for this approach). Gaps are important to elevate the light environment and to reduce competition for soil moisture. It is suggested that planting sites should favour south facing slopes and be in areas with good soil depths so the seedlings have a better chance of long-term survival. Canopy gap creation could involve either felling or ringbarking/poisoning of existing trees.

In addition, some Threatened and At Risk species could also be added within the Te Kakahu Kahukura Project area through enrichment in appropriate sites. For example, fragrant tree daisy and Teucridium parvifolium could be established on the margins of forest or more open streamside sites.

Reference

Forbes AS, Wallace KJ, Buckley HL, Case BS, Clarkson BD, Norton DA. Restoring mature-phase forest tree species through enrichment planting in New Zealand’s lowland landscapes. New Zealand Journal of Ecology. 2020;44(1):3404.

Wallace J, Clarkson BD. Urban forest restoration ecology: a review from Hamilton, New Zealand. Journal of the Royal Society New Zealand. 2019;49(3):347-369. Available from: Urban Forest Restoration Ecology.