The Big Burning Question

At the time of writing, huge wildfires are ripping through forests in Ontario, Canada. In recent years we have seen the same destruction the world over: America, Africa, Australia and several other countries have been heavily affected by wildfires. There is no debate on the outcome of these wildfires; they cause huge damage to the ecosystems they touch, and emit so much pollutant that holes are burnt through layers of our atmosphere causing lasting effects for years to come.

Despite the evident damage that wildfires cause, many people, organisations and governments use prescribed, controlled burning as a tool for managing their land. Why? The short term effects of a controlled burn seem beneficial at the surface level. The fire, if kept under control, slowly spreads through the dead undergrowth of forests, grasslands etc. The old, dry grasses are burnt away. This removes the amount of dead matter that would go up if a wildfire started, limiting the speed and spread of the wildfire and perhaps protecting taller shrubs and trees from burning. In the aftermath of the burning, the ground is a good environment for plants to grow once more. The nutrients of the dead plants have been returned to the soil surface instead of being slowly broken down by weathering and oxidisation. The soil has a coating of a fine, spongy ash which can be better at absorbing water. By all means, a controlled ‘cool’ burn does what it’s meant to. Short term.

However, as with most tools we use to manage land, there are unintended consequences. I will explain these in more detail in this article.

First, some history. Millenia ago, the incidence of fire was low. It happened infrequently. The cause could have been lightning, volcanic activity or spontaneous combustion igniting some dry plant material, as still happens today. Lightning would have been the most common cause but lightning is of course usually followed by a rain, therefore limiting the speed and spread of these fires in the wild.

Wild herds of animals, vast in numbers and diverse in population, migrated across continents, grazing as they moved. An understanding of their impact is crucial in understanding fires and their impact on ecosystems. Herding animals had several positive effects on these grasslands. They would graze, reducing the mass of plant material susceptible to burning. Their dung and urine, in turn, would help cap the soil surface therefore keeping it moist and cool. Their trampling as they milled and moved around would knock down dead plant matter, returning it to the soil surface where it can be biologically broken down.

Very infrequent, periodic fires would not spread far, or burn hot in these conditions. Lush green grasslands do not burn. The rare incidence of a fire would, in places, help create better diversity, giving every plant a fresh start. I suspect that the nutritious, young growth emerging after a fire would attract more animals, therefore beneficially disturbing the soil surface, and leaving it cool and covered as they moved on.

This cycle of events, heavily influenced by herding animals, occurred for a long long time before humans showed up. Even then, it was a long time until we started proactively using fire as a tool to clear brush, making it easier to hunt animals.

With no knowledge of how fire impacts ecosystems, our early ancestors used fire excessively. Used as a hunting technique, this of course declined animal populations over the centuries. More importantly, the impact on the land and the soil of frequent fires was vast. Let me detail some of the most notable:

Frequent burning reduces biodiversity. Fire-resilient and even fire-dependent species of grasses, shrubs or trees start to dominate the environments. The soil surface becomes inhospitable for other species. By reducing this diversity, animals stay away from fibrous, unpalatable species and severely graze any young shoots that try to grow; therefore killing them, further reducing diversity.

Fire exposes the soil surface. Again, this gives potential to new seedlings. But it takes a long time to produce enough litter to re-cover the soil surface, especially in dry environments. Ash is better than bare soil at absorbing rain water but it blows or washes away very easily and there is no plant matter to slow the process. The subsequent bare soil is worse at utilising what little rainfall these dry environments get, further slowly the regrowth.

The term ‘cool’ burn is misleading. Fire is hot, no matter how slowly it spreads. The heat kills organisms in the soil. Organisms that would have helped to build more soil and grow more plants.

A recent trend is the idealisation of indigenous / native practices of food production and land management. In north America and Australia in particular, the use of fire was common. We cannot presume that the practices of indigenous or native people were correct. It is the overuse of fire over the last few centuries that has had perhaps the biggest impact of the degradation of much of the worlds soils, turning thriving ecosystems into deserts.

Even If fire had a more beneficial effect on plants and soils, the atmospheric pollution created by forest or grassland fires should be enough to stop us considering their use as a tool. The emissions of any fire, hot or ‘cool’ are devastatingly high.

Fire is a very unique process that cannot easily be replicated by animals or technology. For that reason it must be considered a tool in our toolkits of land management. However we, as society, evidently do not understand all the implications of using fire, and knowledge of these must be gained before we look to use it. Considering the damage we know burning causes and the emissions we have measured, wide scale use must be seen as a last-resort tool. 1.85 billion acres of the worlds grasslands are deliberately set on fire each year. Reduction of that number needs to be a priority.