Spatial models for monitoring the spatio-temporal evolution of ashes after fire – a case study of a burnt grassland in Lithuania

Abstract

Abstract. Ash thickness is a key variable in the protection of soil against erosion agents after planned and unplanned fires. Ash thickness measurements were conducted along two transects (flat and sloping areas) following a grided experimental design. In order to interpolate data with accuracy and identify the techniques with the least bias, several interpolation methods were tested in the grided plot. Overall, the fire had a low severity. However, the fire significantly reduced the ground cover, especially on sloping areas, owing to the higher fire severity and/or less biomass previous to the fire. Ash thickness depended on fire severity and was thin where fire severity was higher and thicker in lower fire severity sites. The ash thickness decreased with time after the fire. Between 4 and 16 days after the fire, ash was transported by wind. The greatest reduction took place between 16 and 34 days after the fire as a result of rainfall, and was more efficient where fire severity was higher. Between 34 and 45 days after the fire, no significant differences in ash thickness were identified among ash colours and only traces of the ash layer remained. The omni-directional experimental variograms showed that variable structure did not change significantly with time. The ash spatial variability increased with time, particularly on the slope, as a result of water erosion.

How wildfires affect soil properties. A brief review

“…A heterogeneous pattern of soil protection is obtained after fire, which varies with compaction and redistribution of ash. This means that soil is differentially exposed to erosion agents and other processes (Pérez-Cabello et al, 2012;Pereira et al, 2013b). The thickness of the ash layer depends on fire severity: thin ash layers are observed after low-severity fire, while thick ash layers are observed after highseverity fire due to the consumption of larger amounts of fuel.…”

“…Studies carried out by Pereira et al (2013aPereira et al ( , 2013b in Lithuania show that the greatest loss occurred in the first days after fire, as a result of rainfall. They also found that loss of ash was more important in high-severity burned areas, and was caused by erosion and compaction ash layer (Pereira et al, 2013b). In Mediterranean areas, a significant ash layer has been observed during periods ranging between a few days (Cerdà and Doerr, 2008;Zavala et al, 2009) …”

“…Several authors (Hajdas et al, 2007;Eckmeier et al, 2010Eckmeier et al, , 2013Pereira et al, 2013aPereira et al, , 2013b have shown that black colour in burned soils is a consequence of charred litter and black char (black ash produced by incomplete combustion; Robinson, 1991). The dark color reduces the albedo of the soil surface, so burned soils have a high tendency to heat and therefore increase the evaporation rate.…”

“…The study of the thickness of the ash layer shows the degree of soil protection in the period immediately after the fire, and how it changes in space and time (Pereira et al, 2013c). Several studies have been conducted on the effects of ash on soil properties in burned areas which consider the thickness of the ash layer as a key to understand the impact on soil fertility on the evolution of ecosystems in the post-fire (Mallik et al, 1984;Leighton-Boyce et al, 2007;Cerdà and Doerr, 2008;Gabet and Sternberg, 2008;Onda et al, 2008;Balfour, 2008, 2010;Larsen et al, 2009;Zavala et al, 2009;Pereira et al, 2013bPereira et al, , 2013c. The spatial variability of the thickness of the ash layer may be affected by factors such as soil properties and ash texture.…”

Short-term changes in soil Munsell colour value, organic matter content and soil water repellency after a spring grassland fire in Lithuania

“…Incomplete fuel combustion produces black ash (Úbeda et al, 2009), especially in low-severity fires, as in the present one, where the temperatures do not reach high values (Keeterings and Bigham, 2000). Normally, black ash is incorporated into the soil or can be eroded in the weeks following the fire (Pereira et al, 2013b), contributing to the darkening of the soil following the fire and the reduction of Munsell value as observed in this study and in previous reports (Ulery and Relative frequency of SWR for composite and sieved soil fractions, (a) unburned, after the fire; (b) burned, after the fire; (c) unburned, 2 months after the fire; (d) burned, 2 months after the fire; (e) unburned, 5 months after the fire; (f) burned, 5 months after the fire; (g) unburned, 7 months after the fire; (h) burned, 7 months after the fire; (i) unburned, 9 months after the fire; and (j) burned, 9 months after the fire. Graham, 1991).…”