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Ecosystems & Impacts
The sanctuary is situated at the head of a steep-sided stream catchment adjacent to Wellington City. Formerly a part of a lowland forest ecosystem that would have extended over the lower North Island, the valley today is a relatively isolated patch of regenerating lowland forest surrounded by highly modified urban areas, farmland and regenerating shrublands.
Little is known about the pre-European history of the Karori Reservoir Valley, but Maori are not thought to have lived there and it is likely that the valley was primarily used for hunting birds and the collection of food. Indeed, the name 'Karori' is thought to derive from the Maori te kaha o nga rore - the valley of the bird snares. The arrival of Europeans saw the burning of the original forest and the valley was turned into farmland. There was also a short-lived gold rush before the area was set aside as the catchment for Wellington's water supply. Click here for more information about the history of the Karori Reservoir Valley prior to 1995.
As a result, the valley’s forest ecosystem is highly modified. About 20% of the forest cover comprises exotic plantations and the biodiversity of the regenerating native forest has been affected by introduced browsing animals, decline or loss of pollinators and seed dispersers, a diminished seedbank, and competition or exclusion by exotic plant species. Most native animals (bats, birds, reptiles, amphibians and invertebrates) were locally or even nationally extinct due to hunting, predation and loss of habitat, so the forest ecosystem processes have been highly impacted.
The freshwater ecosystem has been similarly affected, not only by two artificial dams interrupting the natural flow of the stream and migration of native fish, and providing habitat for expansion of exotic weeds, but also by deliberate introduction to the lakes of exotic fish (red-finned perch and brown trout), each having impacts on natural ecosystem processes through predation. An annual bloom of cyanobacteria in the lower lake is primarily caused by disruption to the food chain by the exotic fish and periodic mixing of nutrients from the bottom of the lake.
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