In details

Fire and the Ecological Succession


As in all tropical savannas, fire has been an important environmental factor in Brazilian savannahs for many millennia and has, therefore, acted in the evolution of living beings of these ecosystems, selecting plants and animals with characteristics that protect them from the rapid burns that there they occur.

In plants, one of these features that perhaps catches our attention is the cork thick tree and shrub (woody), which acts as a thermal insulator during the passage of the fire.

However, a close observer will notice several other responses of vegetation to fire, such as intense flowering of the herbaceous stratum and rapid regrowth of plants, days after burning, synchronized fruit opening and intense seed dispersal, seed germination. seeds of species that are stimulated by fire.

Still, fire promotes a whole process of recycling of organic matter When burned, it becomes ashes, which are deposited on the soil and, with the rain, have their chemical elements solubilized and made available as nutrients to the roots of plants.

So, contrary to what many people think, the low or moderate intensity fire does not kill most of the Cerrado plants, which are adapted to this ecological factor. In contrast, for many species, especially herbaceous species, fire is beneficial and stimulates or facilitates various stages of its life cycle, as mentioned above.

Also the animals of the Cerrado are adapted to face the burnings: among the vertebrates, many take refuge in burrows or holes and are protected from high temperatures, because, a few inches deep, the soil does not get hot, due to the speed with which the fire goes through the thickets.

But why do savannas - and even savannahs among them - catch fire?

The sparse distribution of trees and woody elements, which characterize the savannas, allows the arrival of insolation at ground level and promotes the development of large herbaceous stratum, forming a grassy "carpet".

Due to their life cycle, these grasses have their leaves and floral parts desiccated in the dry season - which, in the cerrados region, usually goes from May to September. This thin, dry material becomes a highly flammable fuel. Lightning as well as flames and sparks from human actions (burning of agricultural debris, bonfires, etc.) can start combustion of the vegetation and from then on the fire spreads rapidly.

The burns caused by raysSo-called “natural”, usually occur in September, this being the month that marks the beginning of the rainy season in the Cerrados region. This is when heavy, lightning-heavy rains occur, and also when herbaceous biomass is at the peak of desiccation, with its leaves and branches becoming easily flammable material.

Man-made (anthropogenic) burns are often accidental, but can also be intentional.
Compared to natural burnings, anthropogenic ones are usually brought forward to July or August, as this is when most farmers burn the crop remains and prepare their land for new crops, causing the fire to "escape", or when ranchers deliberately burn native pasture to promote regrowth of desiccated grasses and thus provide fresh leaves to cattle at this time of scarcity.