Wildfire contribution to desertification at local, regional, and global scales [Chapter 8]

Abstract

Wildfire is a natural phenomenon that began with the development of terrestrial vegetation in a lightning-filled atmosphere of the Carboniferous Period (307-359 million years before the present). Sediment deposits from that era contain evidence of charcoal from post-fire ash slurry flows. As human populations developed in the Pleistocene and Holocene epochs, mankind transformed fire into one of its oldest tools. Human and naturally ignited fires from lightning altered and steered the trajectories of ecosystem development in most parts of the world. Humans are now the primary source of forest and grass fire ignitions throughout the world. As human populations have increased and industrialized in the past two centuries, fire ignitions and burned areas have increased due to both sheer numbers of people and anthropogenic changes in the global climate. Recent scientific findings have bolstered the hypothesis that climate change is resulting in fire seasons starting earlier, lasting longer, burning greater areas, and being more severe. Computer models point to the Western U.S., Mediterranean nations and Brazil as “hot spots” that will get temperature extremes at their worst. The climatic change to drier and warmer conditions has the potential to aggravate wildfire conditions, resulting in longer fire seasons, larger areas of vegetation consumed, and higher fire severities. Wildfire is now driving desertification in some of the forest lands in the western United States. The areas of wildfire in the Southwest USA have increased dramatically in the past two decades from <10,000 ha yr-1 in the early 20th Century to over 230,000 ha yr-1 in the first decade of the 21st Century. Individual wildfires are now larger and produce higher severity burns than in the past. A combination of natural drought, climate change, excessive fuel loads, and increased ignition sources have produced the perfect conditions for fire-induced desertification. Desertification is about the loss of the land’s proper hydrologic function, biological productivity, and other ecosystem services as a result of human activities and climate change. It now affects 75% of the earth’s land surface and over a billion people. In the past, desertification was considered a problem of only arid, semi-arid, and dry subhumid areas. However, humid zones can undergo desertification with the wrong combination of human impacts. The Amazon region is an example of where forest harvesting, shifting cut and burn agriculture, and large-scale grazing are producing desertification of a tropical rain forest on a large scale. Some of the environmental consequences of wildfires are vegetation destruction, plant species and type shifts, exotic plant invasions, wildlife habitat destruction, soil erosion, floods, watershed function decline, water supply disruption, and air pollution. All of these are immediate impacts. Some impacts will persist beyond the careers and lifetimes of individuals. Small, isolated areas of fire produce noticeable localized desertification. But, the cumulative effect of multiple, large area, and adjacent fires can lead to landscape-level desertification.

Citation

Neary, D. G. 2018. Wildfire contribution to desertification at local, regional, and global scales [Chapter 8]. In: Squires, Victor Roy; Ariapour, Ali, eds. Desertification: Desertification: Past, Current and Future Trends. Hauppauge, NY: Nova Science Publishers, Inc. p. 199-222.