Occasionally, you may hear someone say: ‘1080’s not working. We’ve been using it for 60 years, and we’ve still got possums’. Which might sound like a fair comment, but it fails to recognise a crucial reality: pest control and pest eradication are two very different things. This is the fifth blog in Brent’s PF2050 series.
By Brent Beaven, Programme Manager Predator Free 2050
Pest control is a bit like mowing your lawn: you don’t intend to remove the grass entirely — you just mow it regularly to stop it getting away on you.
Around one-eighth, or 12.5%, of the public conservation estate receives pest control in any given year, and sites are treated at intervals calculated to stop rats, possums and stoats reaching overly destructive numbers.
In forests with lots of food, which support high pest numbers, that might be every three years or even sooner. In less productive forests, that might be every five years.
Now imagine for a moment that you only mowed one-eighth of your lawn once a year, and that you mowed a different eighth each year. What would the grass on the other seven-eighths of your lawn do under such a regime?
This why we still have possums, despite decades of 1080 use.
Sticking with the lawn analogy for a bit, we all know that mowing is a bigger job in the spring and autumn, when conditions are right for grass to thrive.
Similarly, conditions in the forest occasionally become ideal for pests — times when there’s so much food around that they can breed up to their maximum potential. Periodically, whole forests simultaneously produce vast amounts of flower and seed, a phenomenon ecologists call a mast.
For example, when beech trees experience a cool summer followed by a warmer one, they can litter the forest floor between March and June the following year with up to 50 million seeds to a single hectare, many times more than usual.
The magnitude of masts varies across locations and from year to year, but in 2019, beech trees masted pretty much everywhere. So did podocarps — rimu, tōtara, kahikatea, mataī, etc — and in some places, tussocks, in what ecologists called a ‘megamast’.
In times of such abundance predator numbers go through the roof, and that has dire consequences, because once all that seed has either been eaten, or has germinated, plagues of hungry pests need something else to eat. They turn on native wildlife, often just when birds are trying to breed.
Mast seasons come along, on average, every four or five years.
DOC runs a national predator control programme called Tiakina Ngā Manu (formerly Battle for our Birds).
Predator control across large landscapes or remote and rugged terrain costs a lot of money: in 2014 when the Battle For Our Birds predator control programme was launched, it was with a budget of $21 million over five years. Had we met the threat in all affected forests in that period, it would have cost around six times as much.
When a mast loomed in 2017, we had to seek an extra $21m in funding from Treasury to blunt the impact of the mast in addition to the initial five year funding package.
In 2018, within the context of the recently adopted Predator Free 2050 goal, the government increased the budget for Tiakina Ngā Manu to $81.2 million over four years, recognising an ongoing programme of predator control was needed in areas with high ecological values. The programme juggles resources when mast years occur to meet immediate needs while continuing to protect highly threatened native species populations in key areas.
Which is all to say: possums, rats and stoats are costing the country a small fortune.
It’s estimated that invasive predators do more than $450m of damage to the crop and timber industries each year (as laid out in a 2015 BioScience paper). But arguably the biggest toll never appears in the Treasury ledger: Landcare’s John Innes has estimated that every year they devour around 26 million native forest birds chicks and eggs.
Just like mowing lawns, pest control is a job for life — a never-ending game of whack-a-mole that can only ever hold a line in the sand.
Imagine instead if we could rid Aotearoa of stoats, rats and possums completely — forever.
Picture a forest where a mast season was a bonanza for native wildlife, instead of a disaster.
That’s the proposition of Predator Free 2050 (PF2050), but eradicating pests is a whole other magnitude of difficulty and expense.
Back in 2008 I was working on Rakiura/Stewart Island, and did a study on the potential to eradicate invasive predators from the island. At the time, I estimated it would cost between $35 and $55 million to remove invasive predators from Rakiura/Stewart Island alone. That’s between $210 and $330 a hectare, as opposed to aerial pest control, which can cost as little as $20 a hectare.
It sounds expensive, until you factor in the perpetual price of having these predators in the country. At some point, PF2050 would start paying for itself.
So how much would it cost to eradicate predators from all of Aotearoa?
Even if we apply the highest known per-hectare cost — $993 per ha on Rangitoto and Motutapu Islands in the Hauraki Gulf — and a long-run inflation rate of 2.55%, the bill for PF2050 has been calculated at a little over $9 billion over 50 years.
New-generation traps and detection devices are already bringing that cost down, because they reduce labour. By way of comparison, control agencies expect to spend about $15 billion just trying to contain — not eradicate — all known agricultural pests over the same period.
When they deducted the known costs of invasive predators in New Zealand, and added the expected hike in tourism spending that being predator-free would bring, the authors of this 2015 paper found that PF2050 would deliver a net value of $9.32 billion over 50 years, well into the profit side of the ledger.
We’re not yet able to say conclusively how much it will cost to achieve Predator Free 2050 — and that’s mostly because we’re putting a focus on developing the technology and exploring new innovations that will allow us to do the job. Once we are further down the path with this tech, we will be able to cost it.
That said, some things, though, are beyond price: the greatest value of all would come from saving our native biodiversity from extinction, having it thrive, and for our children’s children to be able to experience it.
Doing nothing would be far too costly.
For more about the PF2050 strategy, including a run through of the tools that are going to get us there, visit https://www.doc.govt.nz/moving-towards-pf2050