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International Journal of Wildland Fire International Journal of Wildland Fire Society
Journal of the International Association of Wildland Fire
RESEARCH ARTICLE

How interactions between wildfire and seasonal soil moisture fluxes drive nitrogen cycling in Northern Sierra Nevada forests

Mary K. Brady A , Erin J. Hanan https://orcid.org/0000-0001-6568-2936 A * , Matthew B. Dickinson B , Jessica R. Miesel https://orcid.org/0000-0001-7446-464X C D , Laura Wade A and Jonathan Greenberg A
+ Author Affiliations
- Author Affiliations

A Department of Natural Resources and Environmental Science, University of Nevada - Reno, Reno, NV, USA.

B US Forest Service, Northern Research Station, Delaware, OH 43015, USA.

C Department of Plant, Soil and Microbial Sciences, Michigan State University, East Lansing, MI, USA.

D Ecology, Evolution, and Behavior Program, Michigan State University, East Lansing, MI, USA.

* Correspondence to: ehanan@unr.edu

International Journal of Wildland Fire 31(8) 786-798 https://doi.org/10.1071/WF21064
Submitted: 14 May 2021  Accepted: 2 June 2022   Published: 8 July 2022

© 2022 The Author(s) (or their employer(s)). Published by CSIRO Publishing on behalf of IAWF.

Abstract

As wildfires become larger and more severe across western North America, it grows increasingly important to understand how they will affect the biogeochemical processes influencing ecosystem recovery. Soil nitrogen (N) cycling is a key process constraining recovery rates. In addition to its direct responses to fire, N cycling can also respond to other post-fire transformations, including increases or decreases in microbial biomass, soil moisture, and pH. To examine the short-term effects of wildfire on belowground processes in the northern Sierra Nevada, we collected soil samples along a gradient from unburned to high fire severity over 10  months following a wildfire. This included immediate pre- and post-fire sampling for many variables at most sites. While season and soil moisture did not substantially alter pH, microbial biomass, net N mineralisation, and nitrification in unburned locations, they interacted with burn severity in complex ways to constrain N cycling after fire. In areas that burned, pH increased (at least initially) after fire, and there were non-monotonic changes in microbial biomass. Net N mineralisation also had variable responses to wetting in burned locations. These changes suggest burn severity and precipitation patterns can interact to alter N cycling rates following fire.

Keywords: fire, nitrogen cycling, post-fire soil properties, pre- and post-fire sampling, Sierra Nevada, soil, soil biogeochemistry, soil timeseries, Walker Fire, wildland fire.


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