Port Hills fires: Lessons for the entire country
Planting back quickly and correctly is crucial, writes FIONA CARSWELL, chief scientist at Landcare Research.
The Christchurch Port Hills fires, unlike floods and earthquakes, were essentially a human-created disaster and they will happen again. However, their scale and the risk to life and property can be mitigated.
Prior to human habitation in New Zealand, fires were relatively rare in the lowlands of the eastern South Island. Tall forests and woodlands with trees hundreds of years old grew across the plains and Banks Peninsula. These native forests were damp. They rarely caught fire via infrequent lightning.
Everything changed when humans arrived. Forests were cleared using fire and in their place matagouri, kanuka, grey scrub, bracken and tussock grasses – a huge mass of dry fuel – soon abounded. European settlers then added gorse, broom, wattles, eucalypts and pines and the ecological scene changed again.
Not only did these plants promote fire, they flourished because of it, re-sprouting after fire as few native plants do, releasing abundant seeds that thrived in the nutrient-rich ash and cleared landscape.
The loess soils and steep slopes of the Port Hills are well suited to the stress-resistant native scrub and tussock, and the fire-promoting exotics. This paints a rather grim picture of a vicious and irreversible cycle of fire and regrowth.
The recent Port Hills fires mean the cycle is most evident in Christchurch but already this summer we have seen fires in places such as Thames, Coromandel, Ngaruawahia, the Hakarimata Ranges, Hawke's Bay, North Canterbury and Dunedin.
A study of national fire records back in 2007 showed the number of wildfires had nearly doubled between 1992 and 2007. Many were small and inconsequential and interestingly while Canterbury was statistically significant in the study – 18 per cent of the 4000 fires recorded nationally happened in the province – two thirds of the fires were based in the North Island.
While each fire is unique, the effect on the environment was the same, and that's why New Zealand, not just Canterbury, needs to be cognisant of the risks and dangers and learn how they can be mitigated. And Christchurch can show the way forward.
For many decades, conservationists in Christchurch have worked with city and regional councils, universities, government agencies, fire-fighters and a range of non-governmental organisations and landowners to tilt the balance towards a more resilient, more fire-proof state. Citizens and landowners have put huge efforts into replanting programmes.
However, because of the patchwork of uses and ownership, it is a largely unco-ordinated effort. When the inevitable fire comes, all this progress is swept aside and the post-fire state is worse than before with exotic weeds the main beneficiaries, as this is exactly the environment they evolved for.
Fires in southern California and Australia are regularly in the news. Chile has just suffered the most devastating fires in its history. For many years it has been known that these dry continental climates have the most extreme fire events – natural and human-induced.
But their natural ecosystems are adapted to these conditions. Climate change predictions suggest that New Zealand's eastern south island will become drier and, therefore, more fire-prone. What to plant in these areas and on our burnt hillsides, especially? The choice matters.
The hills are much loved by Christchurch residents for a variety of reasons including recreational use and the visual splendour of the tussock-clad tops that enjoy legal protection to ensure unobstructed views from the Summit Road. The city council manages the Hills primarily via the Resource Management and Reserves Acts and does a good job balancing the competing interests.
We have a very brief window now to influence what will become our generation's legacy to this iconic feature of Christchurch. Inaction will result in rapid regeneration of grass, herbaceous weeds, gorse, broom, pine, wattle, gums and elderberry, with some bracken fern and other indigenous species. Ultimately the fire-loving exotics will prosper the most. These will create new fire risks for nearby property.
Local momentum is growing in favour of an ambitious revegetation programme that will support fire-resistant indigenous species and reduce those risks. This could use a mixture of planting, controlled grazing and sowing seeds that are still attached to branches (for moisture and reduction of grass competition) along with years of careful tending. The Summit Road views and tussocks could still be protected with this scheme, but we may have to forego some of the golden flanks and curtail the regeneration of incendiary pine, gums, gorse and broom.
Are we able to take lessons from our ecological heritage and thwart events such as those which so tragically scorched the Port Hills? The answer is almost certainly, yes.
The answers will come from a coalition of landowners (much of the land is privately-owned), local government, DOC, ecologists, sociologists, fire experts, NGOs, and other stakeholders. The bigger question is whether Christchurch is ready to see itself not just as the Garden City but also as the city that gardened in favour of a more resilient and less-burnable pre-human landscape?
Visit imagery.landcareresearch.co.nz for before and after satellite comparison images of the Port Hills fires.
Fiona Carswell is based at the Crown Research Institute's Lincoln headquarters.