The Ecological Effects of Fires
When the topic of forest fires is ever referred to, it is in the context of the bush fires in Australia and they’re reacted to in the same way as natural disasters such as earthquakes or tidal waves, i.e. they are considered unpredictable, however on the contrary, forest fires can be predictable and with strict, proper planning and management, the effects of fires can be hugely reduced.
As is the custom, the public’s view of fire in a stand would be one of an aesthetic nature; this quite is relevant but the fallout of a fire stretches beyond the “look” of the forest but the future the development and being of the trees and the ever important ecological make up of the soil come into question.
In this essay, I will look into ways in which fire affects not only humans, but our surroundings and also the other co-inhabitants of earth, i.e. animals and other organisms.

Occurrence
If a fire is to start, within the same locality there must exist the combination of a heat source, a fuel and an oxidizing agent. The heat source causes the general temperature of the fuel to rise; it eventually reaches a certain point, called the ignition threshold. At this temperature the fuel (vegetation) releases a flammable gas that is highly consumable as fuel. This fuel the reacts with the oxygen from the oxidizing agent in a process known as “flaming combustion”, a releasing a large quantity of heat, so all in all, the fire can only spread when ignition has already occurred and the heat of the pre-existing fire is high enough to ignite the neighbouring fuel. Further spread of the fire and the rate at which it spreads, rely on two factors, the amount of fuel available and the topography of the land that the fire is expected to affect. The latter is a major factor in predicting the rate and the speed of the fire spreading. It is widely known that fire grow quicker whilst “travelling” uphill and spread slower while moving down a slope. As the height of fire relates to the height of the fuel, heated air from the fire is expelled forward from the flames which further dries the fuel ahead and gradually warms it, increasing the rate of spread. Also, when a fire is reaching the bottom and top of the hill, fires have been known to increase 4 times their original height.
While the topography of the land has much to do with the spread of fire, the climate also plays a key role. Forest fires are most common in areas that possess enough moisture to sustain vegetation growth but ones that also experience extensively hot and dry periods (Pyne). As Ireland’s climate is constantly moisture filled, one where hot and dry spells are very rare, the odds of a hugely damaging fire occurring is large. Fires are much more common in places such as mainland Europe, Australia and western America and other forested parts of the U.S.A. and Canada. In these places, the risk of fire increases sharply during the summer and autumn months as fallen dead branches, leaves and grasses, dry out and become one big reservoir of fuel.
Adding to the already high occurrence of fires, the ever present topic of global warming may also increase the chances. As the number and the length of hot spells increase, drought occurs, leading to bigger and bigger fires that happen more frequently. As a by-product of this, California has seen a severe decrease in numbers of native tree and plant species and almost simultaneously a large increase in the numbers of foreign invasive species such as the snake fern(Lygodium microphyllum) and the drooping brome (Bromus tectorum), that occupy the scorched bare soil.
The climate is not always the factor to blame. It has been recorded in the Mediterranean that 90% of all fires relate directly and indirectly to human activities and behaviours. Such activities include agriculture and forestry (ironically), recreational activities, delinquency and poor general awareness and education. Lightening storms play a lesser role (Birot 2009).

Effects of fire on physical properties of soil
Fire has a significant effect on the properties of soil due to the burning of organic matter located on the soil surface. The changes in organic matter directly have an effect on multiple chemical, physical and biological characteristics of the soil below.
Physical properties of soil that depend on organic matter, include soil structure and pore space and are all sensitive to the heating of the soil during a fire. Clay content, another physical property of soil is not easily affected, except for on the exposed soil surface during an intense burn. An essential soil property that is affected by fire, a property that balances the hydrology of a soil, is water repellence.
During a fire, the organic matter within the litter layer is burnt up, most of it evaporated in the form of smoke but a small percentage of it sinks downwards, following a temperature gradient in the upper level of the soil. It then condenses, forming a water-tight layer that obstructs infiltration, this layer is known as the “water repellent layer”.

Effects of fire on chemical properties of soil
A forest fire planned or not, mainly decreases the amount of nutrients located within the soil, usually through the combined methods of volatilization, oxidation, leeching and erosion. While the overall level of nutrients may be reduced, it is important to remember that the amount of nutrients found on a site and the term nutrient availability to remember that the amount of nutrients found on a site and the term nutrient availability are not the same thing. Although fire decrease nutrient pool sizes, alternatively it has been seen that nutrient availability increase. This is also the case with soil fertility. Soil fertility usually increases after a low intensity burn as fire can chemically convert nutrients locked within dead organic material and the soil surface to more accessible forms.
Closely linked to fire intensity, is site productivity. Following the trend as above, after a high intensity fire, the level of site productivity decreases but site productivity has been seen to increase after a low intensity fire.
Effects of fire on living organisms
Fire has a contrasting effect on a variety of animal communities. The type of effect usually relates to the intensity of the fire, the type of fire and the species of animal. The responses animals’ show from fire includes injury, death, immigration and emigration. Animals with low mobility, very young/old, are more susceptive to damage from fire. The post-fire reactions of a forest, i.e. habitat change, vegetative growth, can have more of an impact on population sizes than the direct damage of the fire itself.
Raptors and other forms of bird of prey are amongst the most successful reactors to a fire, as their prey is more vulnerable due to the loss of hiding cover above. Land based carnivores respond to the effects of fire on small mammal populations, so it can have either a positive or negative effect. Insect populations tend to decrease after fire but sharply increase as new, fresh vegetation grows.
The relationships that people and fire hold are far from simple ones. They vary greatly from community to community and are constantly changing. The effect fire has carries right along the board in the lives of humans, affecting the biology, psychology, technology, economy and politics. Alternatively, people also affect the ways of fire. People increase and decrease the numbers and sizes of fires, they disrupt natural fire systems to suit population and settlement change and also to change the use of the land, for example the “slash and burn” technique that is seen greatly in the developing world, where farmers would clear huge areas of forest through the means of fire to create new sites for agriculture.

Conclusion
It is my belief, as a student of forestry and also a human, that the ways in which forest fires are dealt with and the research that is put into the topic must be constantly held at a high regard. I can say this with confidence due to the plain and simple fact that fire is always going to be a constant factor within the environment in the future as it has been in the past. Although it will be a constant factor, it doesn’t mean it should be a negative one. There are lots of uses for fire, and ways in which people can evolve with and within the controls of future fires.