Forest Restoration

A 500 year journey of restoration

The goal of the Sanctuary forest restoration programme is to have key natural processes operating in the valley with minimal intervention. However, we have almost no way of knowing with any precision what the true nature and complexity of the pre-human ecological processes were, because even forest ecosystems that have not been logged (such as the Wainuiomata catchment) have been severely disturbed by the introduction of alien animals and the collapse of the indigenous fauna.

• There have been some extinctions in the indigenous biota.
• Some exotic biota will never be eradicated permanently (eg weeds, bird and insect pests).
• The fenced Sanctuary 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.

The Karori Wildlife Sanctuary Trust has a 500-year vision for the restoration of the Karori Sanctuary, because it will take hundreds of years for the soil, vegetation and natural processes to change back to a more natural condition.

• Exotic trees like the pines need to be removed and replaced by native vegetation before more natural soil composition and processes can result.
• Forest giants like rata, 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 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.
• To achieve the Sanctuary goal, an active management programme for the restoration of forest flora and forest fauna in the Sanctuary is underway.

The challenge

The effect of possum browsing on trees.

The Karori Reservoir Valley has suffered a number of catastrophic occurrences, which have permanently altered the forest ecosystem. These include forest fires, farming and the introduction of animal and plant pests.

While the aim of the Sanctuary restoration programme is to return the forest to its pre-human state it can never be the same as it once was because certain native biota have been irrevocably lost and some exotic pests can never be fully removed.

Key natural processes & habitat zones

The restoration programme will focus on restoring the key natural processes by removing exotic weeds and animal pests and reintroducing native plant and animal species.

An important consideration for restoration is to ensure that if species are reintroduced into the valley, they are placed in the optimum location to ensure their initial survival and subsequent dispersal. For forest flora this is largely a function of soil, aspect and microclimate. For forest fauna it is largely dependent on the location of food and shelter. To establish a framework within which to make these decisions, five broad habitat zones have been identified, based primarily on optimum sites for certain classes of vegetation.

Each habitat zone is distinguished by its soil type, slope, aspect and climate. Based on these factors a forest type has been identified for the zone. Inevitably there will be natural and gradual transitions between zones and many sites within particular zones will have features of other zones. However, this does provide a framework for the forest restoration programme, because missing or rare plant species can be propagated and planted out in the most suitable habitat for the species.

Habitat zones		Restoration zone map
(click on images for larger view)

Restoration sites

To manage the forest replanting, eight key restoration sites covering 50% of the valley have been identified. Several of these sites have been allocated a volunteer restoration team responsible for weed eradication work and planting of native species in that restoration area. Other sites are often worked on during specified volunteer planting days and weeds might be tackled by staff or volunteers.

Tree planting being undertaken by a Sanctuary Volunteer.

Each Volunteer team receives training and equipment and operates under the overall guidance of the Sanctuary Conservation Scientist.

The remaining 50% of the Valley will not feature in restoration planting, as we wish to have control sites to monitor the restoration programme.