Post-Wildland Fire Desertification: Can Rehabilitation Treatments Make a Difference?

Abstract

Desertification, caused by land degradation as opposed to the immediate creation of classical deserts, is of prime concern in the 21st century. As a result of human activities and climate change, the land loses its proper hydrologic function and biological productivity. Desertification affects 33 % of the earth's surface and over a billion people. Fire-related desertification has a number of environmental, social, and economic consequences. The two key environmental consequences are soil erosion and non-native plant invasions. Erosion after wildland fires can be in the range of <1 Mg ha -1 to 370 Mg ha -1 , depending on fire severity, degree of water repellency, slope, and post-fire rainfall events. Soil losses in the high end of that range definitely exceed soil loss tolerances and contribute to desertification. Non-native plants are typically ten times as abundant on landscapes burned by wildland fires than on unburned lands. Seeding has been used for many years as a prime Burned Area Emergency Response (BAER) treatment. Until recently, this seeding contributed to non-native plant invasions because fast-growing but non native plant seeds were used. The use of native plant seeds and sterile hybrids has reduced this problem somewhat. However, even certified weed-free seed lots have low percentages of non-native plant seeds. Recent use of wet and dry mulches have contributed to reduced postwildland fire erosion rates, but they are quite expensive. This paper examines post-wildland fire desertification and the capabilities of BAER treatments to deal with this growing problem.

FORMATION OF POST-FIRE WATER-REPELLENT LAYERS IN MONTERREY PINE (pinus radiata D. DON) PLANTATIONS IN SOUTH-CENTRAL CHILE

“…Those results suggest the incorporation of post-fire mitigation activities within Chilean policies, focused on the destruction of the water repellent layer, if any, to minimize erosion and maximize soil water infiltration (Leighton-Boyce et al, 2007;Neary 2009). Such activities could consist simply of the mechanical disaggregation by scarification of the first few centimeters of the mineral soil surface or deeper ripping (King, 1981;Robichaud et al, 2000) or increasing soil pH (Karnok et al, 1993).…”

“…Such activities could consist simply of the mechanical disaggregation by scarification of the first few centimeters of the mineral soil surface or deeper ripping (King, 1981;Robichaud et al, 2000) or increasing soil pH (Karnok et al, 1993). However, some land managers use wetting agents such as polyacryl-amide (PAM), a synthetic, high molecular weight organic polymer, to increase the wettability of the hydrophobic soil layer and improve infiltration into the soil (Letey et al, 1962;Wohlgemuth and Robichaud, 2007;Neary, 2009). Additionally, preventive pre-fire activities such as avoiding the accumulation of large amounts of organic matter are as effective as the ones mentioned above (Chan, 1992).…”

Formation of Post-Fire Water Repellent Layers on Nothofagus glauca (Hualo) Forests, After the Historical “Las Máquinas” Wildfire in South-Central Chile

“…The presence of a surface water repellent layer (Pine site) has tremendous implications on runoff production. Considering the same return period for a storm occurring over an area, the magnitude of peak-flow rates after a wildfire can be hundreds of times higher than the ones generated before the burn, when vegetation covered the site (e.g., DeBan et al, 1998;Neary, 2009;Neary et al, 2012). In 4 other words, a surface water repellent layer increases the risk of flooding events, putting in danger human lives and infrastructure.…”

“…As a consequence, it is important to understand the post-fire flood and desertification potential of Chilean ecosystems after the passage of wildfires. Post-fire water repellency (hydrophobicity) is the most relevant variable determining the hydrological effects of a burnt area (DeBan et al, 1998;Garcia-Chevesich, 2005;Neary, 2009).…”

Impacts of Wildfire Severity on Hydraulic Conductivity in Forest, Woodland, and Grassland Soils

“…The development of water repellency has received the most attention and is a test that is frequently carried out as part of wildfire Burned Area Emergency Response assessments (Keeley 2009, Neary 2009). Other mechanisms that have been suggested as major causes of K sat reduction include pore clogging with fine ash and organic horizon destruction.…”