Brook Waimarama Sanctuary's key conservation role
OPINION: Nelson is on course to becoming home to New Zealand's second-largest pest-free, fenced sanctuary.
You may remember the Brook Waimarama Sanctuary's beginnings 15 years ago as a community initiative and probably have heard about some of the controversy surrounding its upcoming pest removal operation, but what makes the Brook Waimarama Sanctuary special and how is it different from others in New Zealand?
Pest-proof sanctuaries provide safe havens for native wildlife. Without such sanctuaries and other, complementary initiatives, introduced pests will continue to kill an estimated 25 million baby birds each year.
The word "pest" refers to non-native species that predate or compete with native species (weka may be a pest digging up your garden but they're native and so don't count!).
There are many pest animal species in New Zealand, including rodents, possums, feral cats and stoats. Removing these pests from the sanctuary will mean that our native wildlife can live and breed as part of a naturally balanced ecosystem.
There are several fenced sanctuaries around New Zealand - from the 40ha Kaipupu Point, a fenced peninsula in Picton, to the whopping 3400 ha of Maungatautari Sanctuary in Waikato.
Its 47km fence encircles an entire volcano! Orokonui near Dunedin and Zealandia in Wellington's Karori suburb fall somewhere in-between.
The Brook Sanctuary is the largest fenced sanctuary in the South Island; its 691ha area is larger than Zealandia and Orokonui combined.
To appreciate the size of the Brook Sanctuary, imagine the outline of our fence overlaid on Nelson's CBD; it would cover all the CBD, from the port to the Maitai Valley.
The first New Zealand sanctuary was the trail-blazing Zealandia. After completing their innovative 8.6km fence, a brodifacoum pest removal operation was carried out to eradicate 13 pest species from the sanctuary.
Since then they have reintroduced 19 species of native wildlife, many of which have now established strong breeding populations spilling out into suburban back gardens.
Before it was a sanctuary, the Zealandia site was a water catchment reserve just like the Brook. Although this status largely protected them both from early development, areas such as the lower valley behind the largest Brook dam were cleared for grazing.
However, much of the higher slopes was never felled, preserving the beautiful mature forest, which provides prime habitat for the re-introduction of native species.
The Brook Sanctuary is dominated by beech species. While Maungatautari recently discovered 100 silver beech trees, thought to be a relic of the last Ice Age, the Brook has all five species of beech in abundance.
Beech trees form the basis of a very large and intricate food web. Mature bark is home to small insects that feed on the sap and create an anal secretion called 'honey-dew' (sorry to dash anyone's fond memories of tasting lovely sweet insect-poo from the trees as a child.).
Honey-dew is a high-energy food source for birds such as tui and bellbirds. It also encourages the growth of fungi that is eaten by many other insects, which in turn are food for birds and tuatara.
Beech forest, like all lowland native forests in New Zealand, has been dramatically reduced in extent.
What remains faces huge threats from introduced pests. In non-fenced areas, pests out-compete native wildlife for food and directly prey on natives.
Beech forests also have "mast" flowering years, when unusually large amounts of seed are produced, providing an important food source for native wildlife.
However, this also produces a boom in pest numbers, as rodents breed very successfully while eating the beech seed and, in turn, predators such as stoats increase in number with the higher numbers of rodents.
When the seed supplies run out, the birdlife comes under attack and, as most New Zealand birds have evolved without defences against such predators, their numbers steadily decline with successive mast years. The presence of this cycle highlights the need to create a beech forest sanctuary in the Brook Valley.
Having other established, fenced sanctuaries to learn from has helped the Brook Sanctuary to have the best systems in place to create and maintain a pest-free environment, as well as establishing successful methods for species reintroduction.
In Wellington, many birds travel beyond the fence to feed, and Wellington is now famous for its urban native bird song. Native birds are repopulating the surrounding suburbs, with saddlebacks breeding in back gardens. This is called the "halo effect."
This process is also underway in Picton, with Kaipupu Point Sanctuary acting as the breeding hub for the wider Picton Dawn Chorus Project. Soon a halo will also be developing in Nelson, which is likely to be even greater in its extent.
The sanctuary backs onto 1660km2 of Mount Richmond Forest Park and is well connected to the Grampians and Marsden Valley, which have community predator-trapping groups in operation.
It is hoped that in time the Brook Sanctuary will bridge the gap between Picton's projects and Abel Tasman's Project Janszoon to re-populate the whole Top-of-the-South with native birdsong.
Besides the great conservation benefits the Brook Sanctuary will bring, the project is ultimately about people -providing a place to experience and connect with our natural heritage in a flourishing natural environment.
Derek Shaw is a former Nelson city councillor and is a trustee of the Brook Waimarama Sanctuary. Fifty Shades of Green is a column contributed through the Nelson Environment Centre.