Wood Decomposition After an Aerial Application of Hydromulch Following Wildfire in a Southern California Chaparral Shrubland

Martin F Jurgensen,Chris A Miller,Deborah S Page-Dumroese

doi:10.3389/ffgc.2020.00093

Abstract

Severe wildfire can affect many soil properties, and organic mulches are often applied to the soil surface to mitigate these changes and reduce erosion, particularly on steep slopes. After the southern California Cedar Fire burned 110,000 ha in 2003, hydromulch was applied to reduce sediment losses. In 2004 we established a study to assess the effect of hydromulch on organic matter decomposition at the soil surface and in the mineral soil using aspen (Populus tremuloides Michx.) and pine (Pinus taeda L.) wood stakes as standard substrates. Mass loss of both aspen and pine stakes in this dry Mediterranean ecosystem was lowest on the soil surface and increased with mineral soil depth. Wood stake decomposition appeared to be lower in the hydromulched soil than in the untreated control, but variability of subterranean termite activity in study replicates and the possible loss of hydromulch soon after application make this result questionable. Termites were clearly shown to have a major role in belowground wood decomposition, and could affect slope stability after wildfire. They also should be considered in planning OM decomposition studies in soils where they are present.

Highlights

High-severity wildfires on steep terrain increase soil erosion and negatively impact water quality in adjacent streams and lakes (Robichaud, 2000; Spigel and Robichaud, 2007; Neary et al, 2012)
Many studies in the United States and in Europe have shown that surface organic mulches generally improve soil chemical and physical properties and moderate soil microclimate after highseverity wildfires (e.g., Dodson and Peterson, 2010; Berryman et al, 2014a,b; Prats et al, 2016; Lucas-Borja et al, 2018b), leading us to hypothesize that hydromulch applied after the Cedar Fire would increase organic matter (OM) decomposition
A soil erosion study conducted near our study site indicated that much of the hydromulch was lost from the soil surface during several large storm events the first year after application (Hubbert et al, 2012)

Summary

Introduction

High-severity wildfires on steep terrain increase soil erosion and negatively impact water quality in adjacent streams and lakes (Robichaud, 2000; Spigel and Robichaud, 2007; Neary et al, 2012). Hydromulch, and Wood Decomposition wildfires in areas with steep slopes (Radeloff et al, 2001; Bautista et al, 2009; Bento-Gonçalves et al, 2012) Such high-severity wildfires remove large amounts of OM from the litter layer and surface mineral soil horizons (Doerr and Cerdà, 2005; Mataix-Solera et al, 2009, 2011), which cause many changes in soil chemical and physical properties (e.g., Baird et al, 1999; Gray and Dighton, 2006; Page-Dumroese and Jurgensen, 2006; Homann et al, 2011). These fires generally have short-term impacts on soil microbial populations but can alter microbial diversity and community structure that affect soil OM decomposition (e.g., Guerrero et al, 2005; Hebel et al, 2009; Page-Dumroese et al, 2019)

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Conclusion