What We Are Trying To Preserve
New
Zealand has developed a unique ecosystem, as it separated from the giant supercontinent
Gondwana millions of years ago, before most mammals had spread to the New
Zealand area. This means that New Zealand’s flora and fauna evolved
separately from other areas of the planet, giving rise to many unique species,
such as the Tuatara Lizard, the only surviving type of an entire branch of
the lizard group. The only mammals native to New Zealand are bats, and other
mammals introduced much later by humans are considered ‘pest animals’,
causing many problems for New Zealand’ native flora and fauna.
There are numerous species of birds found in New Zealand that are found nowhere else. The lack of competition from mammals when those species were first evolving has led to many ground based bird species, such as the national symbol of New Zealand, the Kiwi bird. Kiwis are increasingly rare, in the wild only 10% of eggs escape predation to hatch, and then only 10% of chicks survive past 6 months.
Other bird species that have disappeared from the Tararu Valley ecosystem include the Kokako, Saddleback, North Island Robin, Kiwi, Whitehead, Kakariki, Matata (fernbird), Longtail cuckoo, Whio (or Blue Duck), and Kakapo. Many lizards have also been lost, like Coromandel Striped skink, forest gecko and our recent bat-monitoring shows no sign of either NZ long-tail bats, or short-tail bats, nor of the Dactylanthus plant they feed upon (and pollinate). NZ Falcon & Kaka are only occasional visitors, both being highly vulnerable to mammal predation.
New Zealand's endemic fauna is complimented by equally unique flora. The country hosts a wide variety of tree species including the Northern Rata, Metrosideros robusta, which has developed an interesting way of obtaining sunlight. It begins life as an epiphyte, a tree parasite. As it grows, the Rata sends down its roots. Once they reach the ground, growth increases exponentially and the Rata outlives or out-competes the host. After the host dies, the Rata grows into a massive tree itself which will support a microcosm of epiphytes, lichens, mosses and birdnests..
The
Kauri tree, Agathis australis, is slow to grow but once it reaches
maturity, the trunk width is massive (they can get as wide as 20 metres around)
and the tree's canopy towers over everything else. It is expected that the
Kauri tree can live between 2000-4000 years. Kauri trees produce very good
timber, and many were felled in the late 18th century for building boats and
houses, leaving very few of the big specimen alive. That's why the production
of Kauri timber is carefully managed in modern New Zealand. One Kauri tree
in the Tararu catchment area is more than 1500 years old, and we have named
it "te Tupuna" (meaning 'the grandparent'). It is one of several
extremely old trees in the Valley that have survived the human-wrought change
of the past 150 years.
Our Conservation Work
There are three main strands to our conservation work:
Reforestation
Prior to human arrival, the rainforests of Coromandel Peninsula were dominated by gigantic Kauri trees and other forest giants like Rimu, Totara, Miro, Kaihikatea and Rata. During 1870-1920 the virgin rainforest of Tararu Valley was decimated by logging and gold-mining as the miners used the wood for support-beams and fuel. For most of the 20th century, misguided attempts were made to farm the steep, fragile terrain.
Although we estimate that the forest today represents less than 10% of its original biomass, it still has most of its biodiversity or 'species richness'. This battered ecosystem is recovering slowly and still contains some incredible remnants of the original forest.
One of the major threats to reforestation is erosion. A large storm event in 2002 affected as much a 5% of the land surface. We are working with Environment Waikato to undertake research and monitoring of erosion in the Valley so that we can measure the extent of the problem and record the positive effects that reforestation should have on the stability of the land. In 2003 Thames Coromandel District Council partnered with Tararu Valley Conservation Trust to undertake road- and riverside planting in the Valley. We have also assisted revegation on slipfaces. Harakeke, or flax, are an important revegetation aid as they have deep roots and little vertical mass, meaning they can be planted on eroding slopes without a lot of top-heavy loading, like poplars for example. In addition flax is a great food source for birds like tui.
Humans
can help in reforestation by protecting the birds (who spread seeds) and their
habitat, by dispersing seeds, and also through direct planting. Every year
to date, volunteers have undertaken different forms of revegetation including
planting flax-fans, seedlings, and willow or poplar poles, and now ‘seed
balling’. Based on the work of Fukuoka Masanobu (Author of “The
One Straw Evolution”) seedballs are a method of encapsulating compost
and plant seeds within a big ‘marble’ of clay, which can then
be dropped, rolled or hurled into a location of one’s choice.
By choosing several plant species which are appropriate to each type of target area (eg. shade-loving plants, or fastgrowth ‘hardies’, we can then let Nature decide which plant will flourish in a particular microclimate – rather than forcing the issue as in the case of tree planting.
Bare land can be re-clothed rapidly with pioneer native plants, like Manuka, Toitoi, Karamu (Coprosma species), Akeake, Tarata, Mahoe, Turutu, and more. Once plants that feed birds are established, the birds themselves further distribute the plants around the Valley.
To assist our reforestation efforts, a tree nursery potting shed was built in 2005, followed by a shadehouse for growing on seedlings in 2006.
Pest Control
Stoats, rats, cats, possums, ferrets, weasels, goats, magpies, and pigs all impact heavily on the Tararu Valley ecosystem. Through browsing, predation, and competition, these pest animals have made extinct many NZ species and pushed others to the edge of survival. This has had a knock-on effect on the ability of the forest to regenerate since it is these birds that are able to disperse plant seeds.
For example, the Kereru (NZ wood pigeon) is now the only native bird able to disperse big seeds, like those of Miro, Matai and Tawa. Kereru fall prey to stoats, cats, possums, rats, and poachers; and as they lay just one egg per year, they breed slowly. Without these birds, few Podocarps (New Zealand’s giant coniferous tree family) regenerate and without the trees' food, few pigeons can live in the forest - a vicious cycle that needs to be broken!
Rats also have a significant effect by eating the seeds of many trees. When looking under a single Miro tree, every one of the more than 300 seeds we checked had been chewed by rats.
A pest-proof fence could be the ultimate form of pest control, as it would totally exclude pest animals from an encircled area. Building such a fence is a long-term conservation project – the estimated cost of this work is $250,000 being made of equipment, fence materials, and specialised labour. While the enclosed area has to date been only roughly surveyed, the fence length is estimated at 1000 metres. Therefore the fence cost is approximately $250 per metre and $2.80 per square metre of protected forest. While this fence cost may seem high, when we consider the ecological value of each totally pest-free square metre the true value of this investment is revealed.
In the interim, the immediate goal is to enable the native ecosystem to recover, and protect the local threatened and endangered species, like Hochstettor's frog and Swamp Maire tree. To achieve this we use traps and poison baits, in methodologies accepted by NZ Department of Conservation and IUCN.
Although the forest cannot be entirely free of pest animals (unless the goal of a pest-proof fence is realized) their populations can be kept low enough to enable the native ecosystem to recover. Even by allowing NZ’s long-lived birds to breed successfully occasionally, their population numbers will rebound in time and they can survive with the pests.
Pest control in the forest is a long process involving much hard work, but it is relatively simple work, and very rewarding! All of the traps we use are ‘kill traps’ and are nationally accepted as the most humane methods of control available.
In
the Valley, participation in the killing of these pest animals is absolutely
voluntary and we seek to instil maximum respect for the individual animals
that we kill. They are beautiful and fascinating creatures and it is unfortunate
that past human thoughtlessness has made this work necessary. The consequence
of NOT controlling these animals is simply too great to be an option. For
example: an adult possum eats its own bodyweight every couple of days and
can bear 2 young in 18 months, so killing one such pest animal is the equivalent
of planting many trees. Even more importantly, possums target old trees like
1000 year old Rata, which they can kill in just a few years of repeated browse.
So their control saves old forest as well as allowing young regrowth.
Research & Monitoring
The Earth has many complex elements that are each interrelated. In order to conserve any system or a part of it, such as one species, an intimate knowledge and understanding of the relationships that support the species or make up a community or habitat must be understood. Protection of one species or destruction of one link in the food chain can have wider impacts, and these must be considered.
Natural
systems continually change in response to the environment. By monitoring these
changes we can obtain a sensitive indication of the extent and effect of environmental
changes. Tararu Valley Sanctuary has undertaken a number of research and monitoring
projects such as surveying the canopy coverage in the surrounding bush, the
monitoring of erosion slip faces, and the monitoring of rat populations and
presence of pest animals. The Sanctuary has also hosted research students
from the University of California who were undertaking work on forest health.
Investigation of nature and the study of how ecological systems work helps us to avoid making mistakes that could damage the ecosystem, for example by exploitation or pollution at levels that earth cannot cope with. It can also be used to estimate the level of damage already done. Detailed research gives us an indication of where our conservation efforts can be best concentrated to achieve the best results.
