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New Zealand is home to one of the strangest collections of biological
oddities anywhere in the world. Some of its huge flightless crickets, which
are among the largest insects on Earth, have only recently been discovered.
Meanwhile, the world’s heaviest and most peculiar parrot, the kakapo, is
on the brink of extinction. The country’s plant species also have their
share of peculiarities. New Zealand has the world’s highest proportion of
divaricating shrubs (plants with strangely interlocked and twisted branches),
and tree-sized daisies can dominate the subalpine zone. So unusual are its
plants and animals that Jared Diamond, professor of physiology at the University
of California at Los Angeles, has suggested that they provide the closest
approximation we have to studying life on another planet.

Best known of New Zealand’s surviving oddities is the flightless kiwi,
which has the largest egg in relation to its body size of any known bird.
There are large flightless weevils that live only on large herbaceous plants.
Some of New Zealand’s giant carnivorous land snails measure up to 10 centimetres
across. The country is home to the tuatara, a reptile whose closest relatives
are the Triassic thecodonts. It has one of the most diverse selections of
lizards in any temperate area, with geckos that give birth to live young
instead of laying eggs. And New Zealand has the world’s most anatomically
primitive frogs that nevertheless care for their young. But many of the
strangest and largest animals are either extinct or are presumed so: the
world’s largest gecko, as long as a domestic cat; tiny flightless wrens
with stocky legs; one of the largest eagles that ever lived; and an array
of huge plant-eating flightless birds, moas.

The enormous shrinkage and changes that have affected New Zealand’s
indigenous communities of plants and animals amount to a collapse. The lowland
forest-which is quite distinct from that of Australia in that it completely
lacks eucalypts and acacias-has largely given way to agriculture and plantation
forestry. Vast areas of wetland have been drained, while invasions of alien
plants have altered shrublands and coastal dune communities beyond recognition.
Many mountainous areas retain a cover of native vegetation, but even this
is only a facade, hiding fundamental changes to the original ecological
system. Both lowland and mountain regions have been invaded by alien herbivores
such as pigs, goats, deer, chamois and Australian possums as well as carnivores
such as rats, stoats and cats.

A unique avian herbivore-plant system has been totally lost. Moas formerly
ranged throughout the forest and adjacent open country, and numerous other
birds such as rails, nightjars, wattlebirds, owls and eagles filled the
ecological niches of mammals on continents. Recent studies of cave deposits
and the contents of Maori middens indicate that of about 90 species of endemic
landbirds, found nowhere else, 43 have become extinct since humans arrived
1000 years ago, 9 of them since the arrival of Europeans. This collapse
of the fauna has led Diamond to observe that New Zealand no longer has an
avifauna, just the wreckage of one. Birds are not the only casualties. Nearly
half of the unique native frogs have gone. It is impossible to estimate
the number of invertebrates that have been lost.

Yet New Zealand is better off than some archipelagos because humans
settled the land so recently. The pressing problem is how to save the remnants
from the destruction of their habitats and from the depredations of introduced
predators and browsers.

Unfortunately, New Zealanders themselves see little of what is left.
The salvation of many species depends on the least accessible of the 700
islands around the country’s coast. A few of these islands have remained
free of all predatory mammals, and many others have not been colonised by
cats and stoats. These islands have long been seen as the only viable habitat
for establishing species threatened by problems on the mainland. However,
with the increase in the number of species needing this rather drastic form
of protection, and further invasions, especially by rats, the number of
possible host islands has dwindled. The most recent documented invasion
was by Norway rats, which some time between 1982 and 1984 landed on the
small Whenuakura Island and exterminated a thriving population of tuataras.
Despite international acclaim for successes with bird species such as the
saddleback and black robin, the long-term prospects for many species depend
on whether we can halt the tide of invasions by alien organisms.

However, rare species and communities on many islands are not as seriously
threatened as they were even five years ago. Indeed, there should now be
two ways of increasing the numbers of some of the species most at risk.
The first is to take advantage of the new successes in eradicating pests
from islands, of which there are more than 70 documented examples in New
Zealand alone. The second is to change focus from the slow and expensive
process of trying to help a single species to recover, and to look instead
towards the more cost-efficient strategy of restoring whole communities.

Death to the aliens

Such ecological restoration is not a new idea. Habitat restoration after
mining activities is one example. One of the first attempts at restoring
a whole community began in 1935 under the direction of Aldo Leopold with
the replanting of tallgrass prairie on 24 hectares of degraded farmland
in the University of Wisconsin arboretum. A more ambitious project is that
initiated by Daniel Janzen of the University of Pennsylvania to restore
70 000 hectares of dry tropical forest in Costa Rica. The most comprehensive
attempt to restore an island was undertaken by David Wingate on tiny, 6-hectare
Nonsuch Island off Bermuda. Over almost 30 years, Wingate eradicated five
species of alien plants, goats, dogs, cats and two species of rat. The project
has created salt marsh and mangrove and freshwater swamp habitats, and reintroduced
birds, green turtles and a topshell (a marine snail).

Enterprising projects such as these have raised hopes in New Zealand
of reducing the threats to very rare species at the same time as making
rare communities less vulnerable. This last point is particularly important
because the last refuges for many plant-animal systems are extremely small
islands of 10 hectares or less, some of which are undergoing rapid erosion
and have a geologically limited life. Ecological restoration requires active
management, coordination and considerable planning. The ultimate aim is
to achieve partial or almost complete restoration of biotic communities
in which links between important species or groups of species approximate
the former state of the system.

Restoration has three essential elements. First, there must be a restoration
goal-a model based on historical information or biogeographic interpretation.
This goal must be precisely defined, so that the exercise is not based on
vague ideas and constantly changing objectives. Secondly, it requires active
intervention, to restore those plants and animals that were once present.
Finally, there must be monitoring of progress and further intervention and
active management of the restored area when necessary.

The islands of New Zealand are particularly amenable to restoration
for several reasons. It is relatively easy to define targets because most
of the islands around the continental shelf of New Zealand were once connected
to the mainland during the last Pleistocene ice age, and show little evidence
of endemism. Life on these ‘land-bridge’ islands preserves lowland communities
cut off by rising sea waters. They are biotic capsules of lowland life as
it used to be. By contrast, species living on oceanic islands formed by
volcanoes or as coral keys are descendants of a few hardy vagrants that
often show genetic divergence from their source populations.

Genetic surveys by Charles Daugherty and his colleagues at the Victoria
University of Wellington support the notion that the inhabitants of most
of New Zealand’s islands may be much like those remaining on the main-land.
They compared tuatara living on various islands and found that those living
on islands quite far apart were genetically similar-more so than those living
on some neighbouring islands. Patterns of evolution in island faunas, determined
using new genetic techniques, can help in the development of restoration
targets. Another advantage of islands around New Zealand is that many of
them are in clusters. Mammal-free islands in the cluster can provide models
for restoration programmes aiming to clear neighbouring islands of pest
species.

The best restoration model of all would be to determine what species
had been present before the ecological disruptions brought about by human
activity. There is reason for optimism in that area as well. Archaeological
surveys of Motutapu Island, for instance, have revealed much about its earlier
fauna. Shell deposits left by people can reveal bones of small ver-tebrates,
landsnail shells and fragments of insects preserved by the calcium leached
from the shells. Analyses of pollen in soil can indicate the composition
of earlier vegetation.

The final advantage of islands as targets for restoration is that they
are less complex ecosystems than those on the mainland. All but a few large
islands lacked the interactions that once occurred between the plant-eating
moas and the plants of the mainland. So at least on islands smaller than
10 000 hectares, restoration is not based on processes disrupted beyond
repair.

Several campaigns to restore islands partially, by reintroducing a few
species, usually birds, are already in progress in New Zealand. A new approach
aims to restore all levels of the island communities. One project will try
to integrate restoration with management in the Mercury Islands, a cluster
of 13 islands and islets 6 kilometres off Coromandel Peninsula in northeastern
New Zealand. The Mercury Islands still have an outstanding array of relict
species and communities. These include rare milktree forest, the only known
habitat of the bizarre insect, the tusked weta, two rare species of large
skink, four populations of tuatara and the largest populations of Pycroft’s
petrel.

The restoration programme relies on eradicating rodents living on the
islands. Two islands-one of 31 hectares and one of 18-have so far been cleared
of Pacific rats, in both cases by a single application of rat poison. On
these islands it should now be possible to restore coastal and lowland communities,
which have virtually disappeared from the adjacent main-land. This will
extend the area of unique seabird-reptile and plant-invertebrate communities
now confined to one or two small islands, rehabilitate two populations of
tuatara close to extinction, and establish new populations of the less glamorous
species such as lizards and insects.

To succeed, restorationists have had to decide what kind of management
each island needs and draw up guidelines on how to transfer species between
islands so that the combinations of species are likely to interact as a
viable authentic community. This is not as easy as it might sound. First,
we need to decide how many individuals are needed to start new populations
of small vertebrates such as lizards, even though we cannot be certain how
they will react to their new environment. The number must be kept to a minimum,
as the creatures usually have to be taken from populations that are too
small to withstand repeated depletion if the transfers fail.

But on the positive side, some New Zealand birds including the saddleback
have thrived when transferred to new islands, producing two and even three
times the normal number of broods per season. The first species transferred
within the Mercury Islands was the rare Whitaker’s skink, reintroduced to
Korapuki from neighbouring Middle Island in 1988. No one yet knows whether
they have produced offspring, but zoologists have recaptured pregnant females.

The success of the project will now rely on raising sufficient funds
to carry out the major eradication and reintroduction programmes, and on
the solution of some unexpected problems. One of these is the possible conflict
between ecological restoration and archaeological investigation-a technique
that helps to define goals. When rats have been eliminated, burrowing seabirds
may thrive. Some archaeologists are now concerned that restoration will
eventually cause damage to archaeological sites. The larger the islands,
the more numerous are their archaeological sites. But several larger islands,
of between 100 and 200 hectares, house near-extinct populations of threatened
species and are now feasible targets for rodent eradication and ecological
restoration.

One group of islands south of New Zealand, the Snares, supports more
nesting seabirds than live in the whole of the United Kingdom. These birds
form the base of some island ecosystems by importing nutrients from the
surrounding seas and immediately incorporating the material into soils through
their droppings. The intense burrowing activity aerates the surface soil
and provides an ideal environment for invertebrates and lizards. The same
turnover may accelerate deterioration or bury the complex terraces, garden
sites and dwelling areas left by Maoris after centuries of occupation.

Some of the world’s foremost conservation biologists have suggested
that New Zealand provides many lessons to biologists elsewhere. But these
lessons must first be confronted in New Zealand. It is not enough simply
to slow the rate of extinctions; there is the added need to view conservation
as a responsibility to restore disrupted ecological processes. This need
has been defined-and ignored-for almost 50 years. It is time we took up
the challenge.

David Towns is an ecologist with the New Zealand Department of Conservation.
Ian Atkinson is an ecologist with the New Zealand Department of Scientific
and Industrial Research.

Further reading Ecological Restoration of New Zealand Island, edited
by D. R. Towns, C. H. Daugherty and I. A. E. Atkinson, Conservation Sciences
Publication No. 2, New Zealand Department of Conservation, PO Box 10-420,
Wellington, New Zealand.

* * *

The chronicle of a biotic collapse

Tranquil scenes such as this attract tourists to New Zealand but hide
the extent of ecological collapse. The forest shown in the photograph is
unique to New Zealand and is confined to the northern third of the country.
The dominant forest tree on ridges and in the foreground is the endemic
kauri. Some individual trees could be more than 1000 years old. This forest
type resembles tropical rainforest in its structure but it has suffered
a wave of extinctions earlier than most tropical areas. Unlike the dry tropical
forests, for which Daniel Janzen advocates restoration using ‘biotic debris
and inocula’ from nearby intact habitats, these New Zealand mainland forests
cannot be repaired with material from neighbouring intact habitats-there
are none left.

Studies of palaeoecology in New Zealand matched with fragments of biotic
communities left on islands chronicle an astonishing tragedy. Irreversible
changes have taken place during the life span of many of the larger trees
in the photograph. As seedlings these trees would have shared their environment
with about 50 species of birds (most of them endemic), 17 species of amphibians
and reptiles and an unknown number of giant insects (all of them endemic).
During their growth to maturity, hunting by humans and a foreign army of
mammalian predators and browsers has caused the loss of 82 per cent of the
bird species along with 65 per cent of the amphibians and reptiles and most
of the giant weevils, flightless beetles and giant flightless crickets.

About half of the original bird species are now extinct. Most of the
remainder are confined to islands, as are most of the reptiles and large
insects. The original plant-herbivore system has been changed irreversibly,
and in places even the process of soil formation has been altered by the
loss of many species of burrowing seabirds that once lived in these coastal
habitats.

On the New Zealand mainland, the forests are empty facades. Their roofs
and outside walls are to some extent still standing, but a glance through
their broken windows shows that the furniture has been stripped: ecological
processes within these forests have been comprehensively disrupted. Alien
squatters have taken up residence, and there is no prospect of removing
their pervading influence. But on an island, we have the chance of at least
partly restoring some mainland communities of the past and reactivating
some of the processes that determined their biological character.