The green walls of China

Growing up on a farm meant that you were familiar with fire. There were always trimmings from shelter-belt hedges to drag into piles to make into bonfires. In autumn, there was barley stubble that was burned off to help get the paddocks ready for their next assignment. There were also internal fires to manage for keeping the house warm and even the barbecues were usually charcoal based.

Fire is an ongoing and increasing threat in dry ecosystems. Image by Adrian Paterson.

Burning stubble was always fun. There was an art to getting a quick and effective burn that didn’t spread out of the paddock and into places that you did not want it to be. You would wait for a still day and be poised around the boundary to put out sparks and wayward flames. Living in South Otago, with its plentiful rain, usually meant that the surrounding fields were lush and green. Fire was unlikely to catch hold in the moist neighbouring pastures and so they formed a natural firebreak to stop the spread of the burning. You would finish the day with a nicely burned paddock, a little too much smoke inhalation, and the sense of a job well done.

Living in Canterbury for the last couple of decades has changed my feelings about fire. Canterbury is a much dryer environment. Fires can get out of control and become very dangerous. In the last few years Lincoln was threatened by a wildfire that came within 1 km of the outskirts. The Port Hills had an immense wildfire that threatened the city and had me driving through raining ash to evacuate the in-laws. There have been numerous smaller fires that have nearly got out of control. In short, fires have the element of danger that was largely absent in South Otago. When I see stubble burn-offs now, or any smoke on the horizon, I can’t help but feel a little apprehensive.

A major issue with controlling fires in Canterbury compared with my childhood South Otago is the relative absence of green and lush vegetation surrounding drier areas. Because of the local climate, most vegetation in Canterbury is dry and very flammable by early autumn. There are few natural fire-breaks to halt the spread of a fire. However, there are always some plant species that have a lower flammability than others in any habitat. If we are going to manage future fires then it might help to have more of these species in the landscape. Fires coming up to these low flammability species may halt or at least be slowed enough to be dealt with by other means. This is what is meant by green firebreaks.

The concept of green firebreaks is not a new. It has been used as a fire management tool in various parts of the world for decades (if not longer). However, it is not a common approach as it requires a lot of pre-planning and potentially locking up land that could be producing something else. Still, in our increasingly fire-prone world, green firebreaks look like a good option.

China has a long history with greenbreaks for managing wildfires. There is evidence for firebreaks around 1000AD. A fifth of China is still forested and potentially prone to fires. This has led to the construction of over 350,000km of green firebreaks! Much of the research on greenbreak fire management has been done in China and has been unavailable to most of the science world (which is English language-based). Until now.

Xinglei in the field collecting plants to assess flammability.

In addition to alerting fire scientists to the existence of this research, Xinglei and his colleagues also summarised what has been found. Some examples: Green firebreak species (and the report identifies a number of useful species) tend to produce damper, more humid, understories with lots of fungi to break down leaf litter. Those that are effective should run perpendicular to likely advancing fires (usually perpendicular to the prevailing wind). Firebreaks on ridges are particularly effective. The width of a green firebreak should be at least 10m in most conditions. And so on.

Xinglei Cui, and his PhD advisory team at Lincoln University (Tim Curran, Adrian Paterson, Sarah Wyse, Azar Alam) and University of Auckland (George Perry), have searched through the Chinese published science on greenbreaks and published a summary of what has been found in the Journal of Environmental Management.

Not only do green firebreaks work well in slowing and stopping wildfires but they are useful between fires for enhancing local biodiversity. Green firebreaks block radiant heat that can allow firefighters to approach fires more easily. Green firebreaks are relatively easy to maintain (certainly compared with bare-land firebreaks).

Green firebreaks on the top of ridges are very effective at halting fires (as seen here on the Port Hills). Image by Adrian Paterson.

Xinglei and colleagues were also able to identify areas in need of research. There is little information on where green firebreaks failed to work well. It would useful to have this information. Green firebreaks have mostly been used in a limited number of ecosystems and trials in different habitats and parts of the world would be useful. Finally, there has been little research into how green firebreaks could work in with other fire suppression methods.

The east coasts of New Zealand are likely to continue to become dryer and warmer, which will increase fire risk. Green firebreaks may be one useful solution that can make us all feel a little safer about living in these fire-prone habitats. The kind of solution that will make me feel a little more comfortable when I see smoke in the distance.

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