The soil, the great victim of forest fires

14/02/2017

Fires are part of the plant communities and constitute a phenomenon that is in full study, especially in the case of volcanic soils, called andic soils, as is the case in most of Chile's soils.

The loss of soil caused by erosion after forest fires is the most serious ecological damage, without a doubt. It is not about denying the other consequences of the disaster. The loss caused by fires in forests, crops, properties or people is undeniable, but the soil is the source of nutrients from vegetation and fauna, it is its natural support and its recovery process is very slow. In such a way that the destruction or degradation of its physical, biological or chemical qualities make it the great victim of forest fires.

One of the consequences is erosion, which in the burning grounds appears mainly with the first rains, that is, two or three months after the fire season. After the fire passes, the normal ground cover, which is generally composed of several layers of vegetation (trees, bushes, shrubs, grass, etc.) is literally reduced to ashes, which then disappear with the wind and the first rains of autumn. As a consequence, the surface runoff of the soil increases considerably, doubling the normal values.

The impermeability of the soil surface doubles due to the loss of vegetation cover. The water washes the elevated parts of the topography, laminating it, and at low or broken areas it reaches high speed, building erosion grooves in its path. This physical erosion, visible to human sight, is only one of the consequences, the most serious is chemical erosion, due to the loss of nutrients and loss of soil fertility.

It is true that after the fires, the organic vegetable matter mineralizes and enriches the soil in the form of nutrients, increasing the initial fertility of the soil several times. Because in the first moments there is a greater contribution due to the death of roots and the lower consumption of the surviving vegetation. But this phenomenon is very temporary. Most of the nutrients incorporated are lost in a very short time. The vast majority of nutritional elements are lost in the atmosphere because combustion transforms them into volatile and others are lost dissolved in running water.

Therefore, the loss of nutrients is greater the more intense the fire.

Fires also alter bacterial and fungal activity, which are responsible for biological processes of great importance in the soil. In the case of bacteria there is an initial sterilization, due to the effects of the heat wave and the desiccation of the soil, only later, with the fertility and the increase of the pH (when the acidity levels decrease) its recovery is favored. In the case of fungi the same does not happen and they are negatively affected because they adapt better to acidic soils and the increase in pH after the fire hurts them greatly. Mycorrhizae are the most affected.

As if this were not enough, the infiltration of rainwater is prevented by the destruction or deformation of the surface structure of the soil, because as a result of the dragging of ashes and other fine particles, a soil compaction results, which obstructs its porosity, preventing water penetration.

This lack of penetration of the water in the soil and the drag produced by the waterproofing of the soil, lacking a vegetal layer, has a high erosive potential. In addition to being very sedimented waters product of the drag of particles and ash, which makes them very polluting.

Finally, when many organisms die from the action of heat, it causes an evident decrease in the biological activity of the soil. This, of course, can negatively affect the biogeochemical cycles of numerous elements, which depend on the biological activity of the soil.

However, not everything is negative as far as forest fires are concerned.

When the fires are due to natural causes, something that is less frequent, they help maintain the health of the forest thanks to the mobilization of nutrients and the controlling action that the fire exerts on the pests. In the case of low intensity fires, these contribute to maintaining carbon in the soil, thus preventing its volatilization and loss in the form of carbon dioxide.

In short, fires are part of the plant communities and constitute a phenomenon that is under study, especially in the case of volcanic soils, called andic soils, as is the case in most of Chile's soils. , since these soils behave in a very unique way with respect to heat and fire.

Source: BlueberriesChile.cl - BlueberriesConsulting.com