Foliar nitrogen patterns following stand-replacing fire in lodgepole pine ( Pinus contorta var. latifolia) forests of the Rocky Mountains, USA

Abstract

Little previous work has been conducted on effects of natural, high-severity wildfires on nitrogen (N) dynamics. We measured aboveground plant biomass, foliar N, and net N mineralization 2 years after stand-replacing fires in lodgepole pine ( Pinus contorta var. latifolia) forests in Grand Teton National Park, Wyoming, USA. We detected a five-fold difference in foliar N (% dry weight) among 14 species, from 0.77% in the native grass Calamagrostis rubescens, to 3.4% in the native N-fixer Lupinus argenteus and the non-native forb Lactuca serriola. We also observed higher foliar N in the burned stands for four of six species that occurred in both burned and unburned areas. Mean net N mineralization ranged from −23 to +27 mg-N kg soil −1 year −1, and was predominantly NO 3 −. However, total biomass and foliar N, for all species combined, showed no relationships with site, fire severity, or net N mineralization—possibly because of (i) lack of inorganic N limitation, (ii) methodological shortcomings, (iii) spatial structure existing at different scales than we measured, or (iv) insufficient plant biomass at this early stage of post-fire development to respond to local variation in N availability.