Beneath the Blaze

Soil is the ultimate source of our food and substratum. This valuable earthly resource is affected by burns in many ways. A raging fire might alter the soil beneath at molecular levels.

Baking everyone on its trail, clinging smoke and heat onto everything, a fire rages. It’s troublesome! Clean air, freshwater, enchanting forest, critter, and creatures - we lose everything to a bonfire. Just then the fire settles, embers glow out and we assume the trouble is over. Well, not yet. The soil remembers! The blaze severely affects the soil underneath.

Soil is the mother of all creations. It’s a museum of everything and anything that exists and holds up moisture, carbon, gasses, minerals, and billions of microbes within. Soil is the engine of the integrated biome system. It hosts 25% of our planet’s biodiversity. It diligently acts as a nutrient reserve sourcing all the required macro and micronutrients to plants. Holding up and reserving water, soil keeps vegetation hydrated. With capillary physics and its specific heat capacity, it keeps the earth and vegetation in thermal control. As a filtering element, soil purifies water, and detoxifies wastes. As a buffer medium, it offers a good substratum to vegetation.

Also, it’s a versatile habitat for many organisms. A teaspoon full of soil contains more microbes than the total number of humans on earth. Earth’s soil holds up three times as much carbon as all of the earth’s terrestrial vegetation combined. Soil is thus an important medium for climate rehabilitation. From building blocks to silicon chips, soil has scoured our civilization. Soil is the ultimate source of our food and substratum. This valuable earthly resource is affected by burns in many ways. A raging fire might alter the soil beneath at molecular levels.

Fires are not always annoying. Times before, our forest patches used to burn smooth and regenerate naturally. It was periodic and healthy. It's humans who intervened in the cycle and prevented natural burns. Now as more and more debris collects, a spark burns up a whole forest. The temperature rises, making top-notch conditions for soil mutation. Forest technicians often prescribe controlled burning. This maintains a natural cycle keeping the forest healthy. Prescribed burning has been proved to increase soil nutrients and improve overall soil properties. But flames are not easy to plan. Wildfires have a bigger impact on the soil underneath. The flames burn away all the vegetation and organic matter on the soil surface. Such organic matter plays an important role in nutrient holding and soil aeration. Wildfires accelerate nutrient release from organic matter. The organic debris disintegrates, abruptly releasing the nutrients. Nitrogen in soil is heavily vaporized to the atmosphere. Thus, fire burnt soil enriched with nutrients is nitrogen deficit. Whereas the phosphorus content in soil rises higher than pre-fire levels.

Plant roots and organic matter hold up forest soil. A bonfire, thus, clears all the organic holdfast, catalyzing soil erosion. Intense burns transform clay to sand-sized particles making the soil more coarse and erodible. A burnt-up forest is prone to washing off, landslides, and dust storm. Soil microbes are sensitive to temperature change. The heat kills off the soil organisms that gravely interfere with the future vegetation growth scope of the area. The ashes pile up increasing soil pH and heavy metal content but decreasing soil water permeability. A study by Hoffman et al. (2001) reports the presence of a water repellent layer on soil horizons even after 19 months of burn. Similarly, water quality in the soil, nearby streams, and reservoirs also deteriorate. Fire kills off the plant aboveground. The input of dead roots underneath might affect the soil food web for the duration. A stronger fire may even alter the mineralogical assemblage of the soil. The refractive properties of charred soil materials dominate the soil colors for a long. The presence of iron oxides makes burnt soil appear reddish. Forest fires increase the bulk density of the soil, packing up soil particles. Consequently, root penetration gets tougher. Plant intake of water and minerals is thus affected. Secondary succession on a burnt habitat might drastically transform the original ecosystem of the area. Soil micro and macro invertebrates appear reduced in number following forest fires. Some burns promote invasion as well.

A fire thus brings several physical, biological and chemical changes onto the ground. About 50,000 different wildfire incidents burnt millions of acres of forest last year. Recent mega Forest fire caused a loss worth of $100 billion USDs to Australia. These fire incidents transform billions of tonnes of soil around the world. Some transformations lead to desertification. Few studies do indicate the positive influence of fire on vegetation regeneration and forest management. Whatever the outcome, the management of a newly burnt area is essential. Placing commercially available mats and fiber rolls or spraying hydro mulches prevents the immediate risk of erosion. Testing of the soil properties after a fire helps in finding the immediate structure, properties, and nutrient content in the soil. The nitrogen content can be replenished by adding fertilizers, green manures, and planting nitrogen-fixing plants. Fast-growing nitrogen-fixing crops might rehabilitate soil health and nutrition. Plantation of native species helps in quicker regeneration. Similarly, invasive species should be prevented from spreading by using herbicides or by weeding. Using heavy equipment and contouring the landform reduces the risk of erosion. Some countries like the USA spend millions annually on these burnt area rehabilitation programs. Nepal, with 40% of its area under forest cover, should be emphasizing more on burnt area rehabilitation.

Forest fires thus have latent effects on the soil underneath. Proper reforestation and care of a wild ecosystem need good post-fire management. If manipulated well, a forest fire can result in better vegetation and successive growth within a forest biome. Post-fire management is thus vastly important, though underrated.