In need of a burn – the science of fire

[ORIGINALLY PRINTED IN SUIDERNUUS, 25 FEBRUARY 2022]


The impact of the massive fire on the mountain at Napier the week before last was mixed, and even had some benefits, depending on one’s perspective. Mathabo le Roux spoke to Stephen Smuts, chairman of the Napier Conservancy, about mopping up after the fire at Napier.

 

The fire outside Napier devastated some 4 600ha of mountain area. While some lamented the loss of fynbos to the fire, others welcomed some of its positive aspects, one being exactly the beneficial effect on fynbos.

“Fire is part and parcel of the ecology of fynbos so it needs a burn in cycles of on average between 10 to 15 years. If the interval between fires is longer, a certain species may wither and die off as they get too old,” Stephen Smuts, chairman of the Napier Conservancy and the Southern Overberg branch of the Botanical Society tells Suidernuus.

In the past, fynbos was set alight naturally, mostly by lightning. However, man plays an increasing role in setting veld alight, whether on purpose or by accident. Controlled fires, for instance, are a management tool where landowners burn identified areas of veld, both to renew old veld as well as to serve as firebreaks. The latter helps to manage future wildfires that rage out of control.

Stephen Smuts, chairman of the Napier Conservancy.

‘In need of a burn’

“Some areas of fynbos on the mountain were 20 to 30 years old and were in desperate need of a burn,” says Smuts.

Burning fynbos is rather a science. He explains: If the fire cycle is too short – say five to seven years – it can wipe out a species, because some protea species, for instance, are not mature enough to produce flowers.

That in turn means they cannot produce seed so cannot build up their seed reserves.

If the fire runs through the bush before the seeds are ready, no seeding can take place.

Plants that mature earlier then become dominant and plants that take longer to mature can die out, thereby reducing the amazing species diversity of fynbos.

Also the surrounds are affected. Sugarbirds and sunbirds rely on the nectar of mature flowering fynbos to survive. When such proteas do not recover, these birds are forced out of the area until the veld recovers, which could take years.

Fynbos recovery is “fast and slow, and I am not contradicting myself,” says Smuts. He explains that certain species are only seen in the first year after a fire, for instance ground orchids. There is even a fire lily, Cyrthanthus ventricosus, that flowers within 10 days after a fire. Others, such as proteas, will take years to come to maturity and flower.

Fire lily. Photo: Callan Cohen. (Used under the Creative Commons licence without suggestion that the photographer endorses this article. (https://creativecommons.org/licenses/by-sa/3.0/deed.en))


How aliens bedevil the soil

But there is also a fine symbiosis between bacteria underground and the plants atop it.

Fynbos grows in poor, arid soil, which is the reason for the rich variety of fynbos species. The bush takes little out of the soil itself, allowing for many species to flourish rather than a few to dominate. During burnoff, the plant debris from the fire becomes the fertilizer for the next cycle of bush that will grow there.

When fire passes through fynbos it burns quickly and the fire moves on. Not so with alien species, such as pine and acacia, which burn much longer and more intensely, particularly when they have been felled but not removed, says Smuts.

“The heat just goes deeper and deeper into the soil. All the bacteria and living life in the soil that supports fynbos, is destroyed. So even if you try to replant in the exact same spot with seeds that you have harvested elsewhere, it won't work, because the soil has to be supportive as well. You will see the scaring for a long, long time.”

In parts of the mountain at Napier no alien clearing has been done for a long time. This accounts for the fierceness of the fire in parts.

“There hasn't been stewardship of the mountain. The mountain has been allowed to become completely pine covered … on the Elim part of the mountain the fire raged like the Australian bush fires where the flames are up to 40 metres high, which you don't get with fynbos.”


Manage it!

The conservancy is now looking to workshop strategies to manage the problems that have arisen out of alien invasion itself, and not just how to react to future fires.

The greatest problem is the cost of alien clearing, which is enormous with no immediate commercial benefit.

“You do it for altruistic reasons,” says Smuts. And one of the longer-term downsides of the fire is that aliens such as Port Jackson, much like fynbos, have seeds that are stimulated to germinate by fire. This means that areas on the Napier Mountain previously under fynbos, may well now seed Port Jackson, postulates Smuts.

This has massive clean-up implications post-fire.

Some State support, disbursed by the Department of Agriculture, Land Reform and Rural Development’s Landcare programme, was channelled for alien clearing after the big fire of 2008. Early efforts were not very successful, but another round of clearing organised in 2018, yielded excellent results in several areas because proper targets were set, Smuts says.

The problem of alien debris that stokes hotter fires holds potential, however. In the move away from fossil fuels to combat climate change alternative heat sources have become sought after. And where could that come from? Perhaps from cutting down and removing alien vegetation, suggests Smuts.