Long-term fire effects on soil and vegetation nitrogen cycling: potential links to persistent stream nitrate export
| Authors: | Allison E. Rhea, Timothy P. Covino, Charles C. Rhoades |
| Year: | 2026 |
| Type: | Scientific Journal |
| Station: | Rocky Mountain Research Station |
| DOI: | https://doi.org/10.1071/WF25145 |
| Source: | International Journal of Wildland Fire |
Abstract
Soil and stream nitrate (NO3−) concentrations often increase after severe fire from elevated nitrogen (N) mineralization and reduced plant uptake. However, it is unclear how long these effects persist and contribute to stream N export.
We examined the contribution of soil N supply and vegetation N demand to 19-fold higher stream NO3− export that has persisted since the 2002 Hayman Fire in Colorado, USA.
We compared soil N pools, inorganic N production, subsurface (0–100 cm) NO3− concentrations, vegetation cover, productivity and N demand 17 years post-fire. We sampled along burned and unburned hillslopes to evaluate whether near-stream vegetation and soils attenuated N loss during downslope transport.
Mineral soil, leachate and groundwater NO3− concentrations were higher in burned than unburned hillslopes, despite similar mineralization rates. Burned uplands showed 62% lower productivity and 28% lower N demand relative to unburned forests. Riparian recovery exceeded uplands but remained incomplete relative to unburned conditions. Burned uplands acted as N sources, with slight reductions in soil NO3− in downslope riparian soils.
Sustained NO3− export was driven by reduced vegetation N demand and subsurface transport, not increased mineralization.
Revegetation of severely burned uplands and riparian zones may enhance long-term N retention.