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Low-intensity frequent fires in coniferous forests transform soil organic matter in ways that may offset ecosystem carbon losses.

Published version
Peer-reviewed

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Authors

Pellegrini, Adam FA  ORCID logo  https://orcid.org/0000-0003-0418-4129
Finnegan, Colin 

Abstract

The impact of shifting disturbance regimes on soil carbon (C) storage is a key uncertainty in global change research. Wildfires in coniferous forests are becoming more frequent in many regions, potentially causing large C emissions. Repeated low-intensity prescribed fires can mitigate wildfire severity, but repeated combustion may decrease soil C unless compensatory responses stabilize soil organic matter. Here, we tested how 30 years of decadal prescribed burning affected C and nitrogen (N) in plants, detritus, and soils in coniferous forests in the Sierra Nevada mountains, USA. Tree basal area and litter stocks were resilient to fire, but fire reduced forest floor C by 77% (-36.4 Mg C/ha). In mineral soils, fire reduced C that was free from minerals by 41% (-4.4 Mg C/ha) but not C associated with minerals, and only in depths ≤ 5 cm. Fire also transformed the properties of remaining mineral soil organic matter by increasing the proportion of C in a pyrogenic form (from 3.2% to 7.5%) and associated with minerals (from 46% to 58%), suggesting the remaining soil C is more resistant to decomposition. Laboratory assays illustrated that fire reduced microbial CO2 respiration rates by 55% and the activity of eight extracellular enzymes that degrade cellulosic and aromatic compounds by 40-66%. Lower decomposition was correlated with lower inorganic N (-49%), especially ammonium, suggesting N availability is coupled with decomposition. The relative increase in forms of soil organic matter that are resistant to decay or stabilized onto mineral surfaces, and the associated decline in decomposition suggest that low-intensity fires may promote mineral soil C storage in pools with long mean residence times in coniferous forests.

Description

Funder: Sequoia Parks Conservancy


Funder: Gordon and Betty Moore Foundation; Id: http://dx.doi.org/10.13039/100000936

Keywords

Sierra Nevada, carbon, coniferous forest, extracellular enzymes, fire frequency, nitrogen, soil organic matter, soil respiration, Carbon, Ecosystem, Fires, Forests, Soil, Tracheophyta

Journal Title

Glob Chang Biol

Conference Name

Journal ISSN

1354-1013
1365-2486

Volume Title

Publisher

Wiley
Sponsorship
National Institute of Food and Agriculture (2018‐67012‐28077)