Official website of the New Zealand Farm Forestry Association


PESTS AND DISEASES OF FORESTRY IN NEW ZEALAND

Fragile ecosystems facing threat?

From Biosecurity issue 17, February 2000.

At MAF’s SPS seminar, Dr Oliver Sutherland pointed out the potential environmental impacts of international trade.

Biodiversity in New Zealand

New Zealand was the last substantial landmass to be settled anywhere in the world, only about 1,000 years ago. And prior to that it had been isolated for many tens of thousands of years from Gondwanaland.

As a result of that lengthy period of isolation we have a unique assemblage of species. In fact, over 90% of our species are endemic: they’re found nowhere else in the world. That includes both our species of bat; we didn’t have any mammals in New Zealand prior to the arrival of humans other than three species of bat, of which one has become extinct. All four frog species are endemic, all 60 reptiles, a quarter of all of our birds, over 90% of all of our invertebrates and 80% of our vascular plants. (Just by comparison with these thousands of species found nowhere else, in Great Britain there are just two endemic species: one plant and one animal.)

These species, of course, are assembled into ecosystems. These are not significant just in terms of their conservation and biodiversity values. They provide ecosystem services such as pure water, nutrient cycling, soils, waste decomposition and so on, that underpin primary production.

And you can put a figure on these values. In 1997 indigenous biodiversity was valued at $230 billion per year, more then twice the GDP of $84 billion in that year. And although you can’t easily put a figure on it, of course our clean green environment is what underpins so much of our primary production and our tourism, which we market relentlessly.

Threats to biodiversity

New Zealand, as well as being the last land to be settled, has the worst record of biodiversity loss. A major threat to biodiversity in New Zealand was the arrival of the first humans. By the year 1600, about 600 years after the first settlement by Maori, 33% of our indigenous forests had gone. By 1990, 66% of our indigenous forests had been cleared, and there had been extensive modification of wet lands, dune lands and coastal areas.

Meanwhile we have gained 31 species of exotic mammals, 24 of which have become major pests; particularly possums, rabbits, stoats, ferrets, goats, horses, six species of deer, and wallabies. We have introduced some more within the past few years including, most recently, chinchillas, which are not pests yet but may be.

We have also had 200 species of invasive weeds introduced. And a statistic that I think is worth remembering is that since the early 1800s, one new plant species has become naturalised in the Auckland region every 80 days.

One of the ways in which this happens occurred to me not so long ago. I received in the mail an envelope airmailed from the United States as a trade promotion. The trade promotion was addressed to me not at Landcare Research but Landscape Research. The promoters had gone through the internet and got all the addresses that seemed to have Landscape in it, and they sent me some products that “would preserve landscape value and stop soil erosion.”

The envelope included a packet of seeds called Plantago insularis. It turned out the 200 seeds in this little packet, which I still have in my office, are of a species that is not in New Zealand. When we did a risk analysis on that species we found that it would be a substantial weed risk if it were ever grown in New Zealand. I, along with a whole lot of other people, just got it in the mail.

Impacts on species

In the past 700–800 years nearly one third of our endemic land-based birds have become extinct. Eighteen percent of our endemic sea birds have become extinct. Insects, frogs, reptiles and a bat, and in fact 1,000 of our known animal, plant and fungi species today, are threatened, if not endangered. We have had this extraordinary history of loss of biodiversity as a result of impacts largely through the arrival of humans.

Exotic disease or pest threats posed by international trade

This is the backdrop against which we discuss the threats of exotic diseases and pests posed by international trade.

Endemic plants can clearly be affected through imported primary produce of all sorts; ornamental plants and other goods carrying exotic pest eggs, larvae, and adults.

Endemic birds can be put at risk through imported poultry products and/or stock, and new avian species and/or their genetics. I refer particularly here to ostriches and emu. Even though in New Zealand we do have ostriches and emu, we may lack at the moment the vectors that could transmit their diseases to some of our native birds. These vectors could be introduced.
Looking at reptiles, there is a continuing wish to trade in pet and recreational species of turtles, tortoises and lizards. The endemic crustacea, especially our freshwater crayfish, and other invertebrates, may be threatened through imported chilled and frozen processed foods. New aquaculture species pose a potential risk to indigenous crustacea and invertebrates.
There is also a risk to humans and other endemic biota simply through imported insect vectors; mosquitoes for instance that can arrive and threaten public and animal health.

Phytophthora

A concrete example that these risks are real is Phytophthora, a well-known root-rotting pathogen of commercial plants. Recently in Australia, and also North and South America, Phytophthora cinnamoni has devastated native plant biodiversity. There are widespread virulent strains in Australia, possibly of south-east Asian origin. It attacks over 130 non-commercial native species in Tasmania, some of which are members of families that occur in New Zealand.

Phytophthora cinnamoni is also present in New Zealand, although we don’t have the particularly virulent strains. But under the SPS agreement I guess we could say that we have it in New Zealand so there is no need to look for it in ornamentals that might be imported with roots, soil or artificial soil with the vermiculite attached. So there’s very real risk that I don’t think is being considered in respect of Phytophthora and, no doubt, other diseases that could affect our native plants.

Cabbage tree

One national icon recognisable to most New Zealanders is the cabbage tree. But it’s not so beautiful when being attacked by cabbage tree sudden decline. The story of this brings us back into a New Zealand context.

Cabbage tree sudden decline has been noticed in New Zealand in about the past 20 years. It causes rapid decline and death of trees. But it took the best part of 12 to 15 years for scientists to determine that it was caused by transmissible phytoplasma.

Phytoplasmas are organisms that are very difficult to detect and will be difficult to find on traded ornamentals and other plants coming into New Zealand. The phytoplasma affecting cabbage trees is transmitted by another exotic species (a leafhopper that came probably from Australia), but perhaps of more worrying significance is that phytoplasma has a wide host range which includes commercial species in Australia.

The point here is that there are some quite substantial concerns we could have about plant diseases that are very hard to detect, getting into New Zealand either through trade in ornamentals or trade in primary produce.

Kiwi

The kiwi is a national icon for New Zealanders like no other. We have three species of kiwi; all of them are threatened and two probably endangered. And I believe there may be a risk to kiwi from non-host specific viruses of ostrich and emu.

Before I go on I want to refer to the extreme measures that New Zealand took, measures I don’t think were necessarily justifiable scientifically, to test whether or not rabbit calicivirus disease was going to be a threat to kiwi. Many virologists, and perhaps most scientists, would not have thought there was really much of a risk to kiwi from rabbit calivcivirus disease. But there was an immense amount of publicity causing experimentation done to determine that there would be no risk.

There wasn’t such extraordinary care taken when emu and ostriches, which are ratites in the same family as kiwi, were brought into New Zealand. And I think that in relation to the diseases of those birds cross-species changes in disease manifestations are going to be very difficult to predict before such new species are introduced.

Conclusion

Where does all this get us with the SPS agreement? The wording of the SPS agreement is certainly wide enough to cover any threat to any plants, animals and indeed to the New Zealand environment. But you don’t have to look very far to see that the implementation of the SPS agreement has had a very clear focus on the agricultural and horticultural sectors.
I think it is time now, perhaps even overdue, for an explicit concern for the potential environmental impacts of international trade.

Oliver Sutherland, Science Manager: Biosecurity and Pest Management, Landcare Research

 

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