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Protecting our
natural heritage

Protecting our natural heritage

Image: Moko the gecko with friends Weta and Pīwakawaka holding a PredatorFreeNZ trap

Protecting our natural heritage


“New Zealand is as close as we will get to the opportunity to study life on another planet.” – Jared Diamond

  • Aotearoa’s evolutionary history and isolation created a world where the absence of mammals resulted in an explosion of biodiversity seen nowhere else on Earth.

“Control of mammalian herbivores is likely to be one of the most significant and cost-effective options for protecting and enhancing the country’s massive stores of natural carbon.”Hacknell and Robinson June 2021

The context: the Moa’s Ark of Zealandia

Aotearoa is home to a smorgasbord of unique creatures, some stemming from ancient families long since vanished elsewhere in the world. This is because our islands sit on what has been described as the ‘eighth continent’ of Zealandia (Fig. 1), a mass of continental crust that stretched and thinned so much after breaking away from the supercontinent of  Gondwana 83 million years ago, that most of it sank beneath the ocean.

Then, around 20 million years ago, something changed. The tectonic plates began to compress, colliding with one another, the Indo-Australian plate pushing towards and subducting—riding over—the Pacific plate. Over millennia, relentless forces lifted up a staggering 20-kilometre thick section of the Earth’s crust along the Alpine Fault. In the warm wet world of Miocene, rainfall eroded the mountains, what we now call Kä Tiritiri o te Moana Southern Alps, almost as rapidly as they were thrust upwards. A handful of ancient creatures from Gondwana, like the tuatara and Archey’s frog whose lineage predates the dinosaurs, survived the epic voyage though time. They were joined by birds, bats, and the insects and small reptiles that drifted on flotsam to reach the shores of newly created land. Glaciers came and went; carving out valleys. In warmer periods huge braided rivers carried the eroded material to the shallow coastal margins, creating mega-deltas that eventually merged into wide plains. Together with volcanoes—including Taupo, one of the world’s dangerous ‘mega volcanoes’—a unique, isolated world was created, one in which biodiversity exploded. It was also one in which the earliest ground-based mammal-like creatures such as the St Bathans mammal ultimately failed. And, like the loss of the dinosaurs millions of years earlier, that failure paved the way for something extraordinary.

Fig.1: The lost continent of Zealandia (grey) still beneath the ocean.

“Nowhere else had birds evolved to become the ecological equivalent of giraffes, kangaroos, sheep, striped possums, long beaked echidnas, and tigers.” – Prof. Tim Flannery, The Future Eaters

Giant insects—weta—took over the role that small mammals filled elsewhere. Many birds gave up flying. Some learned to climb trees and dig burrows. Each creature adapted to a rich diversity of landscapes from boiling hot springs and windswept tussocklands to rainforests that flourished besides glaciers.

The problems: introduced predators & pests

When Polynesian settlers arrived around 1250 A.D., they set about clearing the land, burning off native forest, and hunting the large flightless moas to the point where the giant birds became extinct. With their prey gone, the world’s largest raptor, the Haast’s eagle (with a wingspan of up to 3m) vanished as well. But it was the species that these first settlers brought with them that really changed the natural equilibrium: mammals.

While their pigs and dogs would have had some impact, it was the Kiore or Polynesian rat that would eventually become one of the lead players in the extinctions that followed. Soon, endemic geese, ducks, the Waitaha penguin, the adzebill, rail, species of coots and wrens were wiped out.

But these losses did no go unnoticed. By the time European’s arrived, Maori had learned the limits of Aotearoa’s resources and had started to live within them, becoming kaitiaki, guardians of the land and its taonga, its precious natural resources.

Aotearoa: a hotbed of endemism

Endemism means species that are found nowhere else in the world. New Zealand has one of the highest rates endemism on Earth.

Native means species live in New Zealand as well as other countries. Some, like seabirds, are migratory.

Rates of endemism

  • 100% of reptiles, frogs and bats
  • 80% of invertebrates
  • 84% of freshwater fish
  • 59% of birds
  • 38% of marine species
  • 80% of trees, ferns and flowering plants
    • 93% of alpine plants

Migratory species that breed on New Zealand’s islands

  • 50% of the world’s penguin species
  • 54% of albatross
  • 50% of petrels

Europeans settlers began arriving in the 1700s, precipitating a new wave of extinctions. They started ‘acclimation societies’ with the goal of recreating the world they had left behind. Showing a complete disregard for endemic and native species, settlers felled and burned forests, turned what they saw as ‘useless’ grass and shrublands into pastures, drained life-giving wetlands, levelled dunelands that defended the coasts from Antarctic storms, invaded braidplains and confined their rivers, and released wave after wave of exotic species. Releasing deer, tahr, wallabies, chamois, trout, domestic sheep, pigs, cows, goats, rabbits, dogs, tahr, salmons, trout, and countless invasive plants and trees, the settlers drastically and in some cases irreversibly changed the biota.

Endemic species had not evolved to compete with these invaders. Strategies developed over millions of years, such as nesting on the ground, became easy takeaway meals for introduced predators: stoats, ferrets, weasels, hedgehogs, rats, mice, feral cats, and possums. The latter were introduced for the fur trade, but, along with other introduced herbivores, they eat our endemic and native trees and plants, and they have developed an appetite for native animals (Fig 2.).

The settlers also introduced a long list of invasive plants and trees, including willows that are decimating our waterways and pines for forestry, many of which have now gone rogue. The once wide braidplains became glutted with weeds that predators used as cover to sneak up on ground-nesting birds.

Fig. 2 Possums and ship rats are two of the biggest killers in our native forests (Image CC BY NC 3.0 NZ Nga Manu Images)

Today, ninety-four species of birds have been listed as ‘extinct’ along with three lizard species, 75% of frogs, and an unknown number of invertebrates; some likely to have provided important ecosystem services as pollinators and decomposers crucial for storing carbon in the soils and for recycling nutrients.

New Zealand now has the unenviable reputation of having the largest number of threatened and critically endangered endemic species in the world:

This includes 90% of all seabirds, 84% of reptiles, 76% of freshwater fish, and 74% of terrestrial birds. And this may well be an underestimate. An additional one-third of named species are listed as ‘data deficient’. It is likely many more would be on the threatened list had they been assessed. Then there are the species that have not been named and we have no idea about.”  – Prof. Mike Joy & Julia McClean

Almost two-thirds of rare ecosystems are now threatened by collapse. This disastrous situation isn’t news. As far back as the early 1800s the damage that stoats were doing to birds was recognised. Some critically endangered bird species were relocated to island sanctuaries. Restoring native vegetation, removing predators, and applying husbandry strategies to multiple species has hauled many back from the edge of extinction.

Saving a single species is one thing. But what about entire ecosystems? Most species depend on the complex interactions between one another, so many are not suited to captive breeding. Were these strategies just creating temporary arks for the last of Zealandia’s unique creatures?

Solution #1: Get rid of introduced predators

In 2012, Professor Sir Paul Callaghan introduced an idea so bold that it took a while for the scale be realised:

Let’s get rid of the lot. Let’s get rid of all the damn stoats, all the rats, all the possums, from the mainland islands of New Zealand. We start with Rakiura Stewart Island. And we work our way up.

Fig. 3: Greg Brynes from Tuhaitara Coastal Park running a trapping workshop at Woodend. Trapping ‘roadshows’ around the country attract hundreds of people of all ages and demographics, all wanting to be part of the most ambitious conservation project on Earth. (Image: S. Whitelaw)

In 2016 the government-led ‘Predator Free 2050’ campaign was launched, with the ambitious goal to rid New Zealand of possums, rats, and stoats by the year 2050. While almost a third of our land (over 8 million hectares) is in public ownership with some degrees of protection, predators don’t read signs, and they ignore fences and lines on maps telling us who owns what. So an independent Predator Free NZ trust was established to help coordinate activities across organisations, businesses, and the wider community. The concept has been embraced (Fig. 3) and today, predator free projects are being created and developed all over the country.

The goal is not to kill, but to save our unique ecosystems. And to do that successfully, we need to get rid of other invasive species.

Pest plants

While the PredatorFree 2050 campaign has proved wildly popular, other introduce pests are having an impact that in many places are just as devastating. Species such as willowbroom, and Russell lupin have invaded braided rivers, changing their natural dynamic nature and destroying their specialised and vital ecosystem functions including cleaning water from the high level of nitrates generated by dairy farms. Old man’s beard has a particularly devastating impact on native vegetation, climbing over and smothering established trees, forming a dense canopy that stops sunlight reaching the ground. This affects the health of the existing native vegetation and prevents the germination of all other species. Conifers are creating huge problems outlined here. Some species have now gone rogue. In spite of $11 million/yr spent to control them, they’re spreading at a rate of ~5% annually.

Pest herbivores

While the problem of rabbits and hares is generally well understood and accepted amongst agriculturalists, the much larger problem of terrestrial herbivores and trout and salmon introduced for hunting and fishing are mostly disregarded. This because we are still living with the legacy of those early ‘acclimatisation societies’, in which game species are protected.  This has created a bizarre situation where introduced pest species are protected over many endangered and critically endangered species, many of which are not protected at all  (see this article for some keen insight).

The problem becomes extremely emotive when any attempts are made to cull excessive numbers of deer and tahr, both of which are cause significant damage to native ecosystems, resulting in staggeringly high level of carbon dioxide emissions (Fig. 4).

Fig. 4: Estimates of the annual methane emissions (CH4) from introduced herbivores. The equivalent carbon dioxide emisssion eCO2 is on the right. (Image: Hackwell et al, 2021)

New Zealand alpine ecosystems evolved without mammalian herbivores (such as tahr), and many alpine plants have no defence mechanisms (such as toxins or spines) to discourage tahr from eating them. Tahr browse on native plants that birds, lizards and insects use for feeding, nesting and shelter. The tahr diet includes some large, succulent herbaceous species including alpine buttercups and mountain daisies. Some of these species are ranked as Threatened or At Risk by the New Zealand Threat Classification System.” – Department of Conservation

Solution #2: get rid of  pest herbivores

The following is the Executive Summary from:  Protecting Our Natural Ecosystems’ Carbon Sinks by Kevin Hackwell & Maitland Robinson For Forest & Bird, June 2021

Aotearoa/New Zealand could dramatically reduce its net greenhouse emissions by conducting intensive control of introduced herbivores (deer, goats, pigs, wallabies and possums) in native forest, shrub, and tussock lands.

The vast majority of the country’s carbon stocks—over 6,500 million tonnes—are found in our natural vegetation and soils. Nearly 1,500 million tonnes is stored in the above-ground vegetation of our natural ecosystems (mostly native forests). The sheer size of these stocks means that even very small changes in their condition, either positive or negative, can have a significant impact on the profile of the country’s greenhouse gas emissions.

Kāmahi-podocarp forest—the largest native forest type that makes up 10% of all native forest—underwent a significant decline in stored carbon between 2002 and 2014. The most likely cause of this decline was the impact of introduced herbivores. The annual loss of carbon from the kāmahi-podocarp forests was equivalent to 3.4 million tonnes of CO2. This is three times the 2018 domestic air-travel emissions (1), or 80% of the extra annual sequestration that the Climate Change Commission hopes can be generated in the medium term by new native forest plantings.

Introduced herbivores directly consume the biomass of natural ecosystems (leaves, branches, buds, leaf litter, etc.) and produce methane that are estimated to be equivalent to 3.1 million tonnes of CO2 per year. This study estimates that the mid-point figure for carbon sequestration reductions due to browsing damage is a further loss of 8.4 million tonnes of CO2e per year. This is equivalent to nearly 15% of 2018 net greenhouse gas emissions, or nearly 60% of 2018 road transport emissions.

This makes pest control one of the most important and cost effective options available to the country for reducing greenhouse gas emissions, alongside the many sensible proposals put forward by the Climate Change Commission.

The country is currently experiencing a significant increase in the numbers of introduced herbivore, following decades of reduced spending on deer and goat control and little attention to controlling the expansion of wallabies. Natural ecosystems are under induced stress, which includes the collapse of native forest in some areas. If this is not addressed, there is a serious risk that the stores of natural ecosystem carbon will go into decline causing significant increases in net greenhouse gas emissions.

Controlling introduced herbivores will have multiple benefits in terms of ecosystem services and species/ecosystem protection as well as enhancing community resilience to the impact of future climate change. Healthy leaf litter, humus and soil layers, along with greater seedling survival and healthy forest under-story vegetation, will increase the ability to intercept rain and retain moisture. This will help to reduce peak flood flows and extend the flow of water during periods of drought. Maintaining moisture levels will also assist in reducing forest floor temperatures, helping to reduce the risk of forest fires.

This makes it all the more important that cost effective, and sustained control of introduced herbivores country’s natural ecosystems becomes a key ingredient of climate policy. This strategy will assist the country to become carbon neutral, and possibly even carbon positive in the next few decades.

(1) The comparison with components of Aotearoa/New Zealand’s reported 2018 greenhouse gas emissions profile is being used for the purposes of explaining the scale of the impacts of introduced herbivores on the country’s natural ecosystems. It is not done to suggest that introduced herbivore control could be used to offset other sources of GHG emissions. Aotearoa/New Zealand must reduce its present sources of emissions, as well as protect and enhance the country’s natural carbon stocks.

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