Effects of Fire on Trees & Forest

The branch of ecology, which deals with the effects of fire on the ecosystem, is called “Fire ecology” or Ecopyrology. Plants having the ability to withstand fire with little or no damage are referred to as pyrophytes.

It is a major environmental factor. It influences the distribution and development of vegetation. Fire in natural forests is divided into three main types. They are ground fire, surface fire, and crown fire.

The ground fire usually takes place where there is a heavy accumulation of litter.  In dry litter, fire is rapid and extinguishes quickly while in the moist litter, the fire is slow and with its heat, the inner parts also get dried and the fire continues for a longer period.

In-ground fire all herbaceous plants die, but some woody shrubs and trees survive because of their thick protective bark and deep roots. 

Less destructive are faster sweeping surface fire. The flames burn the surface litter and the herbaceous plants. It scorches the tree and shrub by the heat of the surface fire.  Soil also gets scorched at the surface only and after the fire, lots of new seedlings and new shoots emerge by penetrating underground parts.

The crown fire is a forest fire affecting the crown of trees most. It spreads in the top layer from the canopy of one tree to the canopy of another and so on. It kills the trees, shrubs, and herbs most devastatingly. In most soil surfaces, the underground plant parts and buried seeds escape death.

Adaptation of Trees and Wildlife Against Fire

The traits of forest species that enable them to compete effectively in fire-dependent communities may be grouped in four general headings on the basis of their life history features related to fire and site. They are preventing fire damage, recover from fire damage, colonizing sites after the fire, and promoting fire occurrence.

Some tree species like Pinus, Larix, and Quercus, etc.  Develop deep rooting taproot and fire-resistant thick bark with an insulating effect against heat. These trees have tall trunks with self-pruning ability.  Hence, the crown is restricted to the upper zone only.  This helps in escaping the damages against surface fire and ground fire.

Open grown stands (pine) decrease the probability of crown fire and also afford less fuel. Some of the tree species (hardwood) have fire-resistant foliage with lots of water and very little resin or oil content. Rapid litter decomposition reduces the opportunity for fire ignition and spread (sugar maple, basswood, etc.).

Many trees of frequent fire-prone areas like Eucalyptus in Australia have dormant buds, which escape the killing effect of fire and get activated to produce new branches after the fire is over. These buds may be located on the lower part of the trunk and under the soil surface stem and root parts. Some tree species like oaks and hickories develop deep root systems, which escape the killing effect of fire and provides food reserves for rapid regeneration of new shoots after the fire is over.

Seed of certain tree species (pine) has a hard coat, which effectively protects the embryo against the heat of sub-surface soil during the fire. Thus, germination is favored in the favorable seasons by fire, which cracks the seed coats. Certain tree species like Pinus, Arctostaphylos, Ceanothus, and Rhus species have no true dormancy of seeds and germinate at any favorable time following post-fire rains which rapidly grow, elongated, and produce new fruits quickly.  

Some tree species like pine and conifer have flammable foliage and bark. Also, needles of pine and conifers decompose slowly and form and readily fuel the source of the surface fire. Retention of foliage promotes crown fire (firs, cedar, and oaks). Short stature tree species such as jack pine bring flammable foliage close to the ground where a surface fire may spread to the crown.

Fire alters the soil organic matter, total nutrients, pH, and water holding capacity. Soil fungi are reduced while bacteria increase. Nitrogen loss is due to volatilization.

Wildlife Habitat and Fire Forest is influenced more or less by fire which in turn affecting the evolution and behavior of wildlife.

Fire has less effect on mammals and birds than on plants. So, have less attention. Birds have the ability to fly or run quickly for long-distance. Some mammals have the ability to live underground and store food. Due to this functional adaptation of animals, they can survive against fire. However, death among mammals and birds is attributed to smoke inhalation and suffocation than do burning. Soil fauna such as earthworms, snails, spiders, ants, and nematodes, etc are reduced markedly by burning but increase thereafter.

Forestry Bloq
Forestry Bloq
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