The recent disastrous fires on the Christchurch Port Hills give cause for thought as to the best land use on these slopes. It seems that no-one foresaw a fire event of this magnitude. With different wind patterns it could have been much worse. How should this new knowledge about fires risk influence decisions for the future?
Since European settlement, much of the Christchurch Port Hills has been dominated by pastoral farming. In recent decades, we have also seen substantial plantations of pine trees, together with some revegetation of native species.
The Port Hills are also a huge recreational resource for the urban population of Christchurch. On a fine weekend, there are hundreds of walkers and bikers out there enjoying the outdoors. Paragliding and rock-climbing are also much favoured. A lot of this recreation takes place on public land, but some is also through the agreement and support of farmers.
In the forthcoming debate about future land use, there will be lots of people who know the outcome they want. As in all debates, so-called facts will be organised with both self-interest and noble-cause corruption, where ends justify means, coming to the fore.
There will be pro-farming and anti-farming stances. There will be pro-exotic plantations and anti-exotic plantation stances. And there will be pro-recreation and anti-recreation stances.
There are also some thousands of houses on the Port Hills, stretching from Scarborough in the north-east to Kennedys Bush in the south-west. Then further to the south-west, there are lifestyle blocks in behind Tai Tapu.
I live at Kennedys Bush, so my interest is personal. I am often to be found roaming on the Port Hills in the weekends. All of Kennedy Bush Spur (some 200 houses including my own home) were evacuated for periods ranging from three to seven days during the recent fire.
Some of us think there was a substantial element of luck as well as great work by the ground and air firefighters that prevented many more houses from being destroyed, from Kennedys Bush right through to Cashmere and beyond. One can only shudder at the thought of what a strong but dry southerly change might have done at any time on the Tuesday or Wednesday (days two and three of the fire), or if the easterly had chosen to continue throughout that Wednesday night.
I want to step back from immediately focusing on answers, to lay out some issues first. The facts do not always align with what we might want to believe.
We know that the fire started in dry grass, probably caused by part of a transformer or other electrical equipment falling from a power pole. We also know that the spring and early summer had been wet, followed by a dry January and February. As Australian friends remind me, this is the same lethal weather pattern that Australians fear, with vegetative fuel building-up to carry big fires.
Farmers use sheep to control vegetation build-up, and there are thousands of sheep on the Port Hills. But sheep farming is not easy on these summer-dry lands. Domestic dogs can also be an issue – I have come across two sheep carcasses in recent weeks showing undoubted evidence of a dog that had decided on a feast of lamb kidney. Stocking rates are probably lower than in the past, with the economics of fertiliser much more challenging than in the days when wool made a major contribution to sheep-farming incomes.
There are also some cattle on the Port Hills, and I often say ‘hello’ to a herd of Belted Galloways on the Kennedys Bush Track. I hope they survived. But in general, the Port Hills are not really cattle-country.
Poor pastoral economics have led to substantial planting of radiata pine on the Port Hills in recent decades, especially south-west of Cashmere. These land owners have now lost many and probably most of those plantations to the fire.
These plantation losses will inevitably lead to a re-assessment of the economics of radiata pine on the Port Hills. It took some fifty or so years for Canterbury land owners to recognise that growing radiata on the plains was not particularly smart, with exceptional gale-force north-west winds bearing down from the mountains every fifteen or twenty years and knocking down the plantations, often just as they were approaching maturity.
Interest then turned to Banks Peninsula and in particular the Port Hills for growing timber. We now have to ask whether or not fire risk should lead to the same economic conclusion as on much of the plains.
Fires within exotic-pine plantations generate much more heat than do grass fires, and these pine-forest fires are much harder to control. The hot-spots and flare-ups from the recent fire have now continued for close on two weeks since the fire began. If it were not for the pine plantations, my assessment is that the Port Hills fire would have been put out within a day of it taking-off.
It seems that the native forests, once established, have stood up to the fire much better than the exotics. However, the fire did make its way over the crater rim, and then made its way down through native bush towards Lyttelton Harbour and Governors Bay on the other side of the Port Hills. On the Christchurch side, the Kennedys Bush Reserve (located south-west and apart from the Kennedys Bush Spur which has many houses) seems to have survived despite being in a direct line of the initial fire. The native bush in the Hoon Hay Valley also seems to have survived whereas the surrounding exotic plantations have succumbed. But so far, I can only look from afar, as there is no public access.
Those of us who live on the lower slopes also need to ask searching questions about our own properties. There are a great number of fast-growing macrocarpa (Monterrey cypress) and various eucalypt species which are highly incendiary. My wife and I have planted only native trees on our own property, but that decision was unrelated to fire risk. Despite living in Australia for close on 20 years, we gave no thought when we built our house to the possibility of a massive Port Hills fire on the scale we have experienced this year.
Finding the way forward is not going to be easy. My own inclinations are towards grassland on the faces and spurs, and natives in the gullies and on south-facing slopes. This would be similar to pre-European days.
In the long run, recreation is going to be a lot more important than pastoral farming, which will always be marginal on these lands. In a perfect world, the Government would bring more of these lands into public ownership. But then they would need to manage the fire risk themselves, as grassland without sheep, or poorly-managed sheep, would itself be a huge risk.
- For those who wish to understand something more about the geography of the Port Hills and the chronology of the February 2017 fire, here is a link to an earlier article that I wrote.
- The best paper I have found on the historical vegetation of the Port Hills is a paper written and presented in 1919 by Robert Laing, and published in the Transactions and Proceedings of the Royal Society of New Zealand. It is available here.