Thursday, 24 November 2016

Unwanted aliens: is a predator-free New Zealand realistic by 2050?

In a moment of half-baked madness worthy of Donald Trump, the New Zealand Government has announced a plan to make the nation predator-free by 2050. As can be imagined this statement has attracted a wide range of opinions, even from across various conservation groups. These vary from the extremely optimistic viewpoint of Forest and Bird advocacy manager Kevin Hackwell, who claims it is achievable even earlier, to the Green Party's conservation spokesman Kevin Hague, who publicised a University of Auckland study estimating the project's budget at an astonishing if not untenable NZ$9 billion.

With the government prepared to provide just one-third of the plan's funding, it's difficult to imagine which private sector companies would be willing to supply the lion's share over the next three decades. As expected, the response of New Zealand's political opposition has been to pour very cold water on the plan, including the claim that no nation has ever managed to wipe out its population of rats (Hamelin and its Pied Piper notwithstanding).

One of the most essential questions is what is defined as a pest in the context of this proposal?  The relevant Department of Conservation (DoC) page names three principle animal pests: possums, rats and stoats, with a further page expanding the list to other introduced animals and freshwater fish, including cats and dogs (both domestic and feral). Some of the species listed were deliberate introductions, mainly in the Nineteenth Century, whilst others came in accidentally under the radar - New Zealand's biosecurity protocols not always being as draconian as they are now.

A few statistics offer a frightening idea of the scale required: as of 2001 it was estimated that there were seventy million possums in New Zealand, eating 21,000 tonnes of vegetation every night. Needless to say, much of this material consists of endemic species such as pohutukawa and southern rata trees. This then has a knock-on effect for the native fauna that feeds or nests on these species, which of course is in addition to being direct prey for the possum.

Although cats and dogs might be thought of more as pets than pests, even in low numbers they can be devastating to native wildlife. A classic example is the extinction of the Stephens Island wren thanks to a number of feral cats, whilst it is thought that one stray dog managed to kill more than five hundred large brown kiwi in the Waitangi State Forest in less than a year.

DoC's Battle for our Birds scheme relies on aerial drops of poison and ground baits/traps to eradicate the key non-native pests. This year their target area was almost 900,000 hectares; to give an indication of the increase in scale necessary for a nationwide eradication, New Zealand is close to 27 million hectares in total. Perhaps the much-misused term 'paradigm shift' could be safely applied in this circumstance?

At this point it should be mentioned that there are varied opinions as to what the government's planned outcome is. After all, there have been humans living in New Zealand for over seven centuries, so there is little chance of any except the most remote locales returning to a pristine ‘natural' wilderness, even if we knew exactly what that meant. Having said that, the Pleistocene Park project in Russia is attempting something along similar lines. A small region of north Siberian tundra is being converted into glacial period steppe, using musk ox and other large animals as surrogates for extinct mega fauna such as mammoth and woolly rhinoceros. The resulting flora appears to be much more diverse and interesting than the unmanaged wilderness surrounding it, which is ironically the antithesis of what one would expect or hope for with untouched versus deliberately altered landscapes!

Then there's the scale issue: whilst possums, rats and mustelids are relatively easy to track and observe, small species such as wasps and argentine ants are far more difficult to locate, never mind eradicate. Although they don't inflict as much obvious damage to the native flora and fauna, they can nonetheless cause fundamental changes to the ecosystem. Wasps for example eat honeydew, which is an important food source for lizards and native birds such as kaka.

It isn't just insects that would be tricky to wipe out. The rainbow or ‘plague' skink was accidentally introduced from Australia about half a century ago and now seems ubiquitous in Auckland; I've seen it everywhere from volcanos to paddocks, gardens to garages, even inside a bookshop. Thanks to much faster reproduction and maturation rates than native equivalents, it appears to be rapidly out-competing them.

One issue that prevents a complete turning back of the clock is the extinction of dozens of species since the arrival of humans in the country. How can the ecosystem, especially food webs, maintain a long-term balance with key species missing? No-one is suggesting we bring in cassowaries to replace the nine species of moa. Of course, being large creatures they were probably none too numerous, yet there is an hypothesis that they may have been involved in an evolutionary arms race with lancewood, the juvenile trees being well-protected against moa browsing them.

Therefore any attempt to preserve a largely native ecosystem will need to ensure the food webs are fully-functional, with plenty of indigenous pollinators such as short-tailed bats and kereru (native pigeon). Key native species need to identified and preserved just as much as introduced ones removed. This in turn begs the obvious point that since evolution is an ongoing process, are we attempting to freeze the environment at a particular snapshot in time rather than allowing nature to take its course? Even accounting for punctuated equilibrium, natural selection hasn't suddenly stopped in New Zealand any more than it has elsewhere.

The pest-free project will presumably need to tackle species in a certain order, since if mustelids and feral cats are eliminated then rats will proliferate, whilst without rats as prey, the former species will be forced to look for alternative food sources instead; doubtless native birds would form the mainstay of this.

As I have discussed elsewhere, it shouldn't just be the enemies of the native poster species that are targeted. There are plenty of critters less famous than parrot kakapo and ancient reptile tuatara that deserve some attention too, with the endemic weta an obvious example (over twenty percent of its species are currently under threat). Invertebrates play an almost unknown role in nutrient recycling and waste disposal, as well as appearing on the menu of more conspicuous animals. Considering that the takahe, the largest species of swamp hen, was thought extinct for half a century, perhaps we shouldn't be surprised about how little is known concerning the size and condition of native creepy crawly populations. However small and insignificant we might judge them, we ignore their loss at our peril.

Also often overlooked are the native freshwater creatures. Competition comes in the form of the high number of invasive species that compete or predate on them. A key example is the aggressive gambusia, a Mexican fish introduced to eat all the mosquito larvae - which of course it fails to do. Interestingly enough, the DoC website excludes some introduced species from its list of pests: salmon and trout for example are categorised as 'sports fish'. Therefore is economics the government's primary motive for the pest eradication plan, rather than good old-fashioned conservation for the sake of it? After all, the extremely rare takahe was once given second place to herds of elk that had been introduced to serve as a big game animal.

There may be something in this. Mainstream politicians are renowned for their lip service commitment to environmental issues. Could it be that in the wake of the highly negative stories earlier this year concerning exceeded fishing quotas and river pollution, the government is fighting to redeem New Zealand's '100% Pure' brand image?  In addition, agriculture might benefit from an increase in native species' populations. An outstanding example of the latter is shown by a Federated Farmers of NZ estimate that native bees provide pollination services to the tune of NZ$4.5 billion per year!

Finally, we get to flora. As Bec Stanley, a curator at Auckland's Botanic Gardens, is keen to point out, the majority of people have plant blindness compared to their interest in animals. There are thought to around three invasive plant species for every four natives, with old man's beard, gorse, ragwort and nightshade being amongst the best-known culprits. These can smother and kill native plants, thus depriving indigenous animals of food. Despite being vital to the ecosystem, the war on introduced vegetation really seems to be underdeveloped compared to that against non-native animals.

It doesn't take much to upset the balance of at least a local-scale environment. The surviving remnants of mighty kauri forest are currently facing a disease thought to be caused by an introduced water-mould pathogen, a clear case of David conquering Goliath. Without careful consideration, the project to rid New Zealand of introduced pest species could end up doing more harm than good. The motives are potentially dubious and the research chronically under-funded. It remains to be seen whether there is the willpower to see it through or if it is just one more piece of political rhetoric that evaporates by the next election. Personally, I'm in favour of the idea, but uncertain of how realistic it is. Regardless, the citizens of New Zealand need to do their best, lest many more species join the ranks of moa, huia, adzebill and many, many others. After all, who wants their children living in an environment dominated by feral pigeons, rats and possum?