Pinus contorta was introduced at Molesworth Station before World War 2 to slow high-country erosion and the associated human anxiety about it, overlooking the process of mountains seeking their angle of natural repose while endlessly being shoved upward by tectonic plate movement. The station manager and his staff soon also discovered the species was a profuse seeder which the wind easily spread chaotically over the land.
As with the release of the possum for an anticipated fur trade, P. contorta was out of Pandora's Box, yet the wish to deny this is alive and kicking. Everywhere, humans are a disturbing species. It stands to reason that those to follow us will have little memory of the present tawny tussock landscape other than through a photographic record. They will accept a wilding conifer-dominated landscape just as the folk of Arrowtown accept, even relish, the vivid autumn colours of the introduced tree species that provide a landscape more akin to the United States Rockies than Aotearoa-New Zealand.
Then, of course, there are tourists admiring yellow gorse-covered hills and those not uncommon paddocks covered with golden flowering ragwort, not to mention nodding thistles. So what accommodation to the wilding conifer spread can there be? The answer probably lies along the lines written by Jim Childerston (ODT 13.12.12) for such weed trees to be a source of energy as a chip fuel. In its management of the Crown Estate, the Department of Conservation hasn't the money to cope with this invasion. With ever more trees and their dry dross on the ground, a fire simply prepares the site for more seedlings to successfully establish.
Peter Willsman (ODT 26.12.12) pointed out control costs are steep and aerial spraying can result in chemical drift over a town, as happened at Kingston. A further complication is local bodies have large invasive conifers protected in significant tree schedules in district plans.
A radical, pollution free, non-chemical answer could lie in biological control similar to that used by some Central Otago farmers who illegally introduced the rabbit haemorrhagic disease, proving the nation's border protection has more holes than Alison Holst's colander. So why wouldn't some avid, misguided anti-wilding conifer individual smuggle in a few millilitres of Fusarium subglutinam pini (FSP). The very mention of FSP would make any commercial forester suck air through their teeth followed by an unprintable verbal response. The infectious FSP propagules are spread by wind to cause fungal rot and tree death not just to wild conifers but also Pinus radiata plantations.
We should also consider the Moreton Bay fig which grows in Auckland and places further North. A native of New South Wales, it was introduced early in European settlement. Today, a huge specimen is maintained by ratepayers at Pahi, Northland. This tree is recognised as one of the world's largest with a height of 25.7m, a girth of 14.9m and a spread of 48m.
Until 1993, as far as people knew, these Moreton Bay fig trees were sterile and unable to fruit because the tiny pollinating wasp was absent from this country. In 1993, at Westfield, Auckland, botanist Mr Rhys Gardner discovered the tiny wasps. In 1995, the first seedling was found growing in Myers Park, central Auckland. A call went out for a halt to all planting because of its potential to invade and smother native forest and bush remnants.
The fig tree's abundant soft, sweet, sticky fruit is produced all year, to the delight of the birds, rats and possums which spread the indigestible seeds throughout the landscape. While possum feast on pohutukawa, they do not eat the fig foliage because of sticky, white sap in the leaves.
As the possum and fig evolved in the same Australian environment, there seems good reason to believe this is the tree's defence against foliage browsing. The possums can have the fruit because their faeces spread the viable seed.
One can only give a hollow laugh when recalling in 1919 botany and zoology professor H.
B. Kirk of Victoria University, Wellington, was asked by the government to make a study of the possum situation. He found negligible damage to forests but enormous potential for a fur trade. Possums could be released with advantage in forests except those fringed by orchards or plantations of imported species. To use a modern idiom: Yeah right!
