Abstract

We measured soil heating and subsequent changes in soil properties between two forest residue disposal methods: slash pile burning (SPB) and air curtain burner (ACB). The ACB consumes fuels more efficiently and safely via blowing air into a burning container. Five burning trials with different fuel sizes were implemented in northern California, USA. Soil temperature was measured at 1, 2, 3, 4, 6, and 8 cm depth. Immediately after burning, soil samples from two depths (0–10 and 10–20 cm) and ash samples were collected for analyzing organic matter; carbon and nitrogen content; and calcium, magnesium, and potassium concentrations. The highest temperature observed was 389 °C at 1 cm depth under the SPB. Mean peak temperatures were 133.2 °C and 162.2 °C for ACB and SPB, respectively. However, there were no significant differences in peak temperatures and duration of lethal soil temperatures (total minutes over 60 °C) between ACB and SPB. Heat transfer decreased rapidly as the soil depth increased. There is little evidence that any subsequent changes in soil chemical properties occurred, concluding that these small-scale burns had few negative impacts at our study site. Therefore, given the lack of extreme soil heating and more efficient and safer woody residue reduction, the ACB may be more effective than open SPB, especially where fire escape or long-term fire damage to soils are of concern.

Highlights

  • Fire suppression and drought have led to a significant amount of land that must be treated to reduce wildfire risk [1], in California, USA

  • Given the lack of extreme soil heating and more efficient and safer woody residue reduction, the air curtain burner (ACB) may be more effective than open slash pile burning (SPB), especially where fire escape or long-term fire damage to soils are of concern

  • Data from the 1 cm depth under the ACB were lost due to mechanical malfunction. It is likely the 1 cm depth ACB temperature would be similar to the SPB with a similar fuel since the peak temperature at 2 cm depth reached 315.6 ◦ C

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Summary

Introduction

Fire suppression and drought have led to a significant amount of land that must be treated to reduce wildfire risk [1], in California, USA. There are many ecological benefits of forest residue disposal through burning [2,3], but selecting the most appropriate method is important for sustainable forest management [4]. Piling residues is the preferred method for disposal of woody residues among land managers. As an effective fuel reduction tool, slash pile burning (SPB) has been widely used in western USA forests as one method to reduce fire risk and extreme fire behavior [3,5]. SPB has often been selected as the most economically feasible option for disposing forest residues, especially at the wildland—urban interface or areas without local bioenergy facilities [3]

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