This is a post that I wrote (but didn’t publish) in May just before leaving Wellington. An update to the pest control effort made world headlines recently, with NZ’s prime minister, John Key, setting an ambitious goal of eliminating all pests from the country by 2050. This is an extraordinary target, and what it will take to achieve it is nearly incomprehensible to me. But New Zealand’s unique species and ecosystems are – far more than in any other country I’ve yet visited – vitally important to its identity.
In local news recently, this headline appeared: “Record-breaking mast predicted for northern beech forests.” A mast event is when trees produce an unusually large number of seeds. In Maryland, we have masts that create virtual seas of acorns beneath oak trees. In New Zealand, the beech (Fuscospora species, unrelated to the American Fagus) normally produce seeds every 4-5 years, but certain conditions can trigger a massive seed drop. There was a beech mast in 2014, the largest ever seen. Good news?
Not such good news. This huge production of seeds brings with it a huge number of seed-eaters, which in New Zealand are rodents and possums. In the US, we may view an acorn mast as a potential human health problem, because it leads to an increase in the mice that are carriers of the Lyme disease virus. In New Zealand, rodents, stoats (preying on the increased rodents) and possums are the non-native species whose rapid increase following a beech mast can overwhelm human efforts to control them. Here’s a great video put out by a prominent conservation group, Forest and Bird, that describes this scenario.
The New Zealand Department of Conservation (DOC) dealt with the mast repercussions in 2014 by creating a campaign: “Battle for our Birds.” Its goal was to try to inform the public about DOC’s efforts to combat the imminent “pest plague, ” which involved placing even more “1080” and Brodifacoum poison in threatened areas.
Naturally, there are plenty of people who view the widespread use of these poisons as offensive, misguided, dangerous, ineffective, or all of the above. As I traveled from Australia (where it is also used to reduce numbers of introduced mammals)to New Zealand’s South Island, to the North Island, I noted how differently people in these regions seemed to respond to this type of pest control. The “Battle for our Birds” campaign appeared to be more accepted in the North Island, while “Ban 1080” signs were rampant throughout the South Island. In fact, there is now a political party in New Zealand called “Ban 1080.” Their main objections to the use of 1080 appear to be that it is an invasion of public lands, could contaminate water, and that some native bird species can also be susceptible to poisoning (i.e. kaka, morepork, robins). One of their arguments, which I’ve heard echoed by several South Islanders, is that killing possums by poisoning them causes economic hardship for those hunters who make a living selling possum fur.
Beech forests and their endemic species are also experiencing attacks from a different, invertebrate angle: introduced wasps. Honeybees, bumblebees and German (Vespula germanica) and common (Vespula vulgaris) wasps were introduced to New Zealand, but while the intentionally introduced honeybees and bumblebees remain innocuous garden visitors and valued pollinators, the accidentally-introduced wasps have been implicated in numerous ecological problems.
The density of these species is higher here than anywhere else in the world; in some forests, their biomass is greater than that of all the native birds there. These social wasps need protein to feed their young, and have been known to attack, kill, and gorge on hatchling birds in their nests. Warning signs are now common in areas where the number of wasps could seriously threaten humans.
One of the wasp’s most destructive roles has been as a honeydew hog. When you enter a black beech forest in New Zealand, you are struck by a strong fungal scent. This comes from the sooty black fungus that grows on the trunks of the beech trees. The fungus feeds off the sugary honeydew secreted by tiny aphids which have burrowed into the phloem of the trees and extended a thin anal tube out through the bark to release excess sugars. These white hair-like tubes can be several centimeters long, and often you can see a drop of honeydew clinging to the end, unless one of the birds specialized to lap this up – such as a bellbird or tui – has already visited. Or, as is now more often the case, one of the introduced wasp species has been there. These voracious wasps don’t just take the excess drop of honeydew; they consume the tube as well and kill the aphid in the process. In wasp-infested forests, it is estimated that 90% of the honeydew will be consumed by wasps, leaving the birds without one of their staple foods. Since less honeydew means less mold, there is also less food for certain beetle and moth species that have evolved to depend on this food source.
This complicated chain reaction of relationships that humans inadvertently set in motion must now be dealt with by decisions that weigh the perceived relative value of and prognosis for all these species. My personal reaction to the poison bait boxes prevalent in the Wellington bush was first horror, and then a gradual, reluctant acceptance, but I still find the thought of widespread poisoning – which is also the current prevalent treatment for wasps – deeply troubling. This is a country that has experienced devastating loss of endemic species, and it feels like it is fighting an increasingly desperate battle to save those that remain outside the protection of managed sanctuaries and islands. Every intervention is experimental, since major ecological change has occurred so rapidly, and pushed so many species so close to the brink.
From what I witnessed in my few months here, though, if any country can do this, Aotearoa New Zealand can. The spirit of kaitiakitanga, or guardianship, is pervasive and broadly upheld both politically and socially in ways that would not likely be embraced in the US. I’m glad to have gained even a sliver of insight into the ecological complexities of conservation in this country, and I could never have guessed how avidly I would be following news about beech trees.