The goal of our forest restoration programme is to have key natural processes operating in the sanctuary valley with minimal intervention. Our restoration programme focuses on removing exotic weeds and animal pests and reintroducing native plant and animal species.
As close as possible
Our forest will never be exactly the same as before the arrival of humans. This is because:
- We don’t know with total precision what was here before us.
- There have been some extinctions in the indigenous biota.
- Some exotic biota will never be eradicated permanently (e.g. weeds, birds and insect pests).
- The valley has suffered from a number of catastrophic occurrences, which have permanently altered the forest ecosystem – forest fires, farming and introduction of animal and plant pests.
- The fenced sanctuary valley will be a much more closed ecosystem (like an island) than it would have been when it was a small part of a huge unbroken ecosystem.
We can only try and take out the most disruptive elements (animal and plant pests) and put back as many of the indigenous elements as possible and watch and see what happens!
A 500-year journey of restoration
We believe it will take 500 years for the restoration of the sanctuary valley. This amount of time is based on:
- Removing exotic trees like pine and replacing them with native vegetation so that more natural soil composition and processes can result.
- Forest giants like rātā, rimu and miro are rare or missing. It will be a long time before the small trees being planted now reach maturity and natural regeneration of these species is occurring.
- The restoration of native forest in the sanctuary valley will provide habitat for the re-establishment of wildlife species that have disappeared. This is a mutually beneficial relationship as several of our most important tree species (such as tawa and miro) rely almost entirely on birds for transport of their seed and others rely on birds and lizards for pollination.
A biodiversity collapse
There is no historical record of what vertebrate and invertebrate species were present in the sanctuary valley before it was cleared. Assuming the original vegetation was a dense multi-tiered lowland podocarp/broadleaf forest, then it is likely that most forest vertebrates of the southern North Island would have been present. A list of species known to have been present south of the Manawatū River before human settlement forms the basis for our Restoration Plan.
An amazing diversity of animal life probably flourished in the Wellington area in pre-human times. The pre-European forest would have contained bats and birds such as bellbird, bush wren, fantail, falcon, grey warbler, Haasts’ eagle, huia, kākā, kākāpō, kākāriki, kererū, kiwi, kōkako, laughing owl, moa, piopio, robin, saddleback, hihi, tomtit, tūī, weka, and whitehead. There are many stories of the deafening birdsong in the bush around Wellington last century.
Overall, the indigenous fauna of the valley was in a seriously depleted state before the restoration work was begun in 1999, with only about 21% of the previous vertebrate fauna present. Some species are now extinct but it is possible that analogue species might be introduced to replace these.
The valley of the birds
Now that Zealandia is free of significant predators such as rats, mustelids and cats, the remnant populations of native birds in sanctuary valley (such as tūī and kererū) have shown a rapid increase and are spreading beyond the sanctuary borders. Many species of native fauna have been reintroduced (see Progress to date) and more will come over time.
Some species with strong homing instincts may be successfully established in a new area by introducing captive-bred juveniles (e.g. kākā). Other species are so rare in the wild that captive breeding is the only way to source sufficient numbers for release (e.g. pāteke).
Supplementary feeding of birds, such as kākā, hihi and bellbird is important to encourage birds to stay in or return to the sanctuary valley and thereby ensure that breeding populations are established. Supplementary feeders are also useful in that they help staff and visitors see the birds and monitor activities.
Restoring the dawn chorus
The sanctuary developed a 10 year Restoration Strategy in 2000 with a three stage release programme for birds.
Stage 1: Robust species (relatively accessible birds that should be able to coexist with low numbers of predators, assuming there may be breaches of the fence): Re-introduction of this group began within months of the completion of the pest eradication programme in 2000. Included are: bellbird, kākā, kererū, kiwi, tomtit, weka, whitehead and kākāriki (red-crowned parakeet).
Stage 2: Rare or vulnerable species (birds that may be difficult to obtain, may be more vulnerable to predation or may be difficult to establish): Some of these species have begun to be introduced, such as the saddleback and hihi. Others may be re-introduced at a later stage, including kōkako, rifleman and yellow-crowned parakeet. And advocacy pair of South Island takahē were introduced as an analogue the now extinct North Island takahē.
Stage 3: Endangered and analogue species (birds that are endangered in status or rare species that may be introduced as analogues for species that are now extinct): Included are: kākāpō and snipe. These are unlikely to be considered in the near future due to the available habitat.
In regard to other fauna:
There are approximately 40 species of native gecko, divided between the mainly nocturnal brown geckos and the day-active green geckos (which can be seen in the display at the Round Lawn). Of these, five have been identified as appropriate for release into the sanctuary valley, but only the forest gecko is known to be present.
New Zealand also has nearly 40 species of skink – several of which are endangered. Three of the five species identified as appropriate for the sanctuary valley have been found naturally occurring here.
In 2006, we reintroduced tuatara. These are now known to be breeding.
The two extant species of indigenous bat (the short-tailed and the long-tailed bat) have a threatened status so it may be some time before animals can be safely obtained for release into the sanctuary valley. Translocation techniques for bats still need to be developed so any transfers will need to be part of an approved research project.
* Note: Since this was written we have released giant wētā in to the valley
Invertebrates are animals without backbones. Very little is known of which invertebrates would have been found in pre-human times in the sanctuary valley but we have made some best guesses about large-bodied species that should be present. These include: the giant pill millipede, giant wētā, giraffe weevil, speargrass weevil and large land snails.
The question of which native invertebrates should be reintroduced to Zealandia will be the focus of a research programme and will require a systematic survey of what species are already present.
The introduction of any invertebrates will require caution to ensure that potentially injurious exotic species are not accidentally introduced. Quarantine measures, such as using sterilised potting mix during the re-vegetation programme, have been used to limit the risk, and strict biosecurity measures are in place to prevent the accidental introduction of pests such as Argentine ants. Whenever possible, pest invertebrates such as Vespula wasps are controlled.
Forest flora restoration
Early herbarium records and a comparison of plant species recorded in the sanctuary valley with records from other sites on the Wellington peninsula with similar soil types have helped us to determine which native plants are missing and should be reintroduced.
Planting is done with locally sourced seeds from the Wellington Ecological District, or further afield if necessary.
The state of the forest
The emergent layer is dominated by rewarewa on the western slopes, and exotic pines on the eastern side. A small plantation of 80 tōtara remains on the eastern slopes.
Priority has been given to the propagation and planting of podocarps (kahikatea, miro, mataī, tōtara and rimu) and pukatea to re-establish these species in the sanctuary valley. Emphasis will also be given to propagation of the regionally rare northern rātā because it should thrive in the possum-free habitat. It will be many years before there will be a noticeable change in the emergent tree species present and that is one reason why we have a 500-year vision.
Work has begun on the progressive removal of the exotic pines. Apart from some missing species, the canopy layer in the sanctuary valley is regenerating well. Restoration activity will focus on rare or missing species such as black maire and white maire.
Of approximately 65 species of sub-canopy trees and shrubs that should be present, 30% are rare or missing. Many species in this category are characteristic of early and mid-successional stages (e.g. kānuka) and should be present now, particularly as areas of exotic forest are cleared, but they will become rare again in future as the forest matures. Regionally rare species such as whau, large-leaved milk tree and small-leaved milk tree should thrive in the pest-free sanctuary once introduced.
With the absence of pest browsing and weed competition, it is assumed that most species of epiphytes, and lianes present in the sanctuary valley will thrive and not require active management. However missing or rare species such as perching kōhūhū, Kirk’s tree daisy and several mistletoes will be propagated and reintroduced.
The forest floor and weeds
There are some significant climbing pest plants in the valley that are a priority for ongoing management to eradicate them. These include old man’s beard, cathedral bells, banana passionfruit and climbing asparagus. You can see samples of these species at the weed display along Lake Road – along with information on how to control them in your own backyards.
Ferns and their allies are already a significant feature of the sanctuary and new species have been located as the habitat recovers. A survey will be undertaken to identify missing species so that they can be propagated and reintroduced. The exotic spike-moss selaginella has been found and will need considerable effort to remove it.
Very few of the small herbaceous plants and orchids identified as appropriate have been recorded in the sanctuary valley. However, systematic surveys will be undertaken before any substantial effort is made to propagate and plant them.
Reintroduction of missing species will focus on those that are keystone species for invertebrates such as the threatened speargrass weevil that lives on the native speargrass. There are a number of exotic herbs such as Mexican daisy and wandering willie that require ongoing control to eventually eradicate them.
There have been no surveys done of mosses and fungi in the sanctuary valley and this will need to be done before priorities for restoration can be determined.