In the northern hemisphere, where annual average rainfall is around 100 kg per square meter in cold and dry regions, boreal forests, with needle-leaf trees, dominate. The southern hemisphere is dominated by savanna; bushes and meadows occupy millions of hectares.. In these regions, natural fires can be the most important factor of ecosystem changes. When looking at the results of these fires, it sometimes seems they were preprogrammed as to when, where, and how they spread.
Examples of fire dependent ecosystems
The cone of the Jack Pine species (Pinus banksiana), which is widely distributed throughout North American forests, requires absolute forest fire in order to release its seeds. The cone of this species can remain on the trees without releasing seeds for years because of climate and the resin layer covering it. Seeds preserved in the cones wait for the next fire; the cone’s scales open with the heat generated during such a fire. The seeds then start their journey towards a piece of soil that they can grow into. Here the role of fire is very important, not only for the dispersal of seeds but also in preparation of germination. The high humidity and low temperatures in the forests of these regions delays the decomposition of fallen leaves. This layer of dead material over the mineral soil is another hindrance for seeds to meet the soil. When scales of the cones open with the help of forest fire, this thick layer of dead leaves is also removed, having burned down to create fertile new soil.
Another example of fire benefiting plants is the chaparral vegetation of the North American forest. This type of plant cover is composed of short, perennial wooden plants and annual non-woody plants. During the hot, dry weather of summer, this vegetative cover becomes particularly vulnerable to fire. A dark black cover composed of unburned parts, frames, and ashes of the plants is left behind. This sight, which is saddening at first, actually hides various beauties in it, and these beauties only emerge after a series of events.
Figure 1: The overview of a chaparral type vegetation after a fire. Figure 1a: Right after the fire Figure 1b: 2-3 years after the fire.
Golden eardrops (Dicentra chrysantha), which is a member of the perennial Chaparral family, is deeply affected by fire. The seed of this plant requires a fire event in the germination season and should be exposed to smoke for at least 10 minutes.
The positive effects of forest fires can also be seen in the healthy survival of an ecosystem. Due to its thick bark, the widely distributed Ponderosa pine (Pinus ponderosa), of North America, is minimally affected by the low, medium level cover fires that happen every five to twenty years. The weak and unhealthy individuals in this dense forest get burned as a result of natural forest fires, leaving healthy, thick barked trees. This way, possible epidemics of harmful forest organisms, via these unhealthy trees, is prevented. In the meantime, due to periodic fires, dead cover, or fallen and dead trees are removed, thus preventing bigger fires.
In the eastern Mediterranean, brutia pine, yellow pine, black pine, aleppo pine, and stone pine can are widely distributed. Among these, brutia pine is spread across a wide area, especially in most fire sensitive regions. It is created with a thicker bark around the trunk compared to other pines. This species can be minimally impacted from low and medium level cover fires. On the other hand, seeds in the cones of brutia pine are thrown far away by the heat of the fire, reaching fertile germinating grounds, thus helping to spread the forest.
Fuller, M. 1991. Forest Fires: An Introduction to Wildland Fire Behavior, Management, Firefighting, and Prevention, SD421.F84, Wiley & Sons, Inc., NY, pp. 238.
Keeley, J. E. 2007. “Chaparral and Fire,” Fremontia, Volume 35:4, pp. 16-21.
Bond, W. J., Wilgen, B.W. 1996. Fire and Plants, SE18HN, UK, Chapman & Hall, UK, pp. 259.