Sri Lanka's forests are one of the country's richest natural resources, supporting a huge diversity of plant and animal species providing forest products to support local livelihoods. Over the years the forested lands have been deceased drastically due to number of causes. These include clearing for agriculture and large development projects, selective felling of timber, and recently, introduction of invasive species. apart from these factors forest fires can be considered as an agent for forest degradation.
Tropical rain forests in their undisturbed state are nearly fire proof. The stratification structure of the forest helps to keep wetness inside the forest. As tropical forests are opened up for logging and agriculture, they become very fire prone, and produce more died wood than under natural condition and provide fuel for future fires. After a forest is burnt, more light and space is available for grasses and other vegetation to grow on the fores floor. This vegetation dries out more quickly and easily burns. Creating conditions for annual fires.
Knowledge on effect of fire to the forest to the forest is very important for managing degraded forest and plantations. Generally it affects the composition, structure and pattern of vegetation of the landscape. The forest manager faces a complex challenge in managing fire to achieve beneficial effect and avoid unwanted results. Even attempts to eliminate harmful fire can cause undesirable consequences such as increased risk of fire and declining ecosystem health. Thus. it is important that the immediate and long term effects of fire be understood and integrated into forest restoration program.
Causes of Forest Fire
Forest fires are caused by natural as well as man made caused. Many forest fire starts from natural causes such as lighting which set trees on fire. High atmospheric temperatures and dryness offer favorable conditions for a fire to start. Man made fire is caused when a source of fire like naked flame, cigarette, electronic spark or any source of ignition comes into contact with inflammable material.
Even though natural forest fires are not common in Sri Lanka, there are some forest fires which are created by human. These human activities are significant in savanna grasslands because it is an effective tool to prepare lands for agricultural activities. Other than this, some cattle farmers set fire to the grassland for obtaining young leaves to feed their cattle. Not only grassland but also forest plantations such as Pinus and Eucalyptus in dry and low humidity areas are very sensitive to fire. The number of fires reported annually ranges from 50-200 depending on the prevailing weather conditions in Sri Lanka.
Types of Forest Fire
There are to type of forest fires:
1 Surface fire, and
2. Crown fire.
Surface Fire
A forest fire may burn primarily as a surface fire, spreading along the ground as the surface litter on the forest floor and is engulfed by the spreading flames.
Crown Fire
The other type of forest fire is crown fire in which the crown of trees and shrubs burn. Often sustained by a surface fire. A crown fire is particularly very dangerous in a coniferous forest because resinous material given off burning logs burn furiously. On hill slopes, if the fire starts downhill, it spreads up fast as heated air adjusted to a slope tends to flow up the slope spreading flame along with it. If the fire starts uphill there is less likelihood of it spread in downwards.
Damage of the fire to the ecosystem and their subsequent recovery depend on various factors such as fire behavior, fire duration, the pattern of fuel consumption, and subsurface heating. Fire can damage or kill trees through effects on tree species has different vulnerability to fire, which can vary on different site.
fire have both positive an negative effects to the environmental. Most of the public attention inclines to its negative effects. These include the destruction of vegetation, the loss of plants and animal, threats to biodiversity, and erosion in mountain areas when soil is exposed. Moreover fires can create favorable sites for invasive plant species to become established and flourish.
The positive impacts of fire and less widely appreciated. In place where decay is constrained by dry and cold climates, fire plays a dominant role in recycling plant debris. apart from that, fire can induce germination of dormant seeds of some species. Germination of some hand seeds can occur only after fire ruptures seed coat., allowing water to enter. Some seeds require dry heat to induce germination, but are killed by low temperatures if they have imbibed moisture.
Managing forest fire
Wildfire prevention refers to the preemptive methods of reducing the risk of fires as well as lessening its severity and spread.Effective prevention techniques allow supervising agencies to manage air quality, maintain ecological balances, protect resources, and to limit the effects of future uncontrolled fires.Policies may permit naturally-caused fires to burn to maintain their ecological role, so long as the risks of escape into high-value areas are mitigated.However, prevention policies must consider the role that humans play in wildfires, Sources of human-caused fire may include arson, accidental ignition, or the uncontrolled use of fire in land-clearing and agriculture.
Wildfires are caused by a combination of natural factors such as topography, fuels, and weather. Other than reducing human infractions, only fuels may be altered to affect future fire risk and behavior. Wildfire prevention programs around the world may employ techniques such as wildland fire use and prescribed or controlled burns. Wildland fire use refers to any fire of natural causes that is monitored but allowed to burn.Controlled burns are fires ignited by government agencies under less dangerous weather conditions.Vegetation may be burned periodically to maintain high species diversity, and frequent burning of surface fuels limits fuel accumulation, thereby reducing the risk of crown fires. Using strategic cuts of trees, fuels may also be removed by hand crews in order to clean and clear the forest, prevent fuel build-up, and create access into forested areas. Chain saws and large equipment can be used to thin out ladder fuels and shred trees and vegetation to a mulch. Multiple fuel treatments are often needed to influence future fire risks, and wildfire models may be used to predict and compare the benefits of different fuel treatments on future wildfire spread. However, controlled burns are reportedly "the most effective treatment for reducing a fire’s rate of spread, fireline intensity, flame length, and heat per unit of area" according to Jan Van Wagtendonk, a biologist at the Yellowstone Field Station. Additionally, while fuel treatments are typically limited to smaller areas, effective fire management requires the administration of fuels across large landscapes in order to reduce future fire size and severity.
Building codes in fire-prone areas typically require that structures be built of flame-resistant materials and a defensible space be maintained by clearing flammable materials within a prescribed distance from the structure. Communities in the Philippines also maintain fire lines 5 to 10 meters (16 to 33 ft) wide between the forest and their village, and patrol these lines during summer months or seasons of dry weather.Fuel buildup can result in costly, devastating fires as new homes, ranches, and other development are built adjacent to wilderness areas. Continued growth in fire-prone areas and rebuilding structures destroyed by fires has been met with criticism. However, the population growth along the wildland-urban interface discourages the use of current fuel management techniques. Smoke is an irritant and attempts to thin out the fuel load is met with opposition due to desirability of forested areas, in addition to other wilderness goals such as endangered species protection and habitat preservation. The ecological benefits of fire are often overridden by the economic and safety benefits of protecting structures and human life.For example, while fuel treatments decrease the risk of crown fires, these techniques destroy the habitats of various plant and animal species. Additionally, government policies that cover the wilderness usually differ from local and state policies that govern urban lands.
The Larva
The Pupa
Adult moth
The Leaves damaged by larvae
Typical Leaf web made by larva
Early stage of attack
Bushy appearance of crown due to larval feeding
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