title: Slow carbon and nutrient accumulation in trees established following fire exclusion in the southwestern United States.
abstract: Increasing tree density that followed fire exclusion after the 1880s in the southwestern United States may have also altered nutrient cycles and led to a carbon (C) sink that constitutes a significant component of the U.S. C budget. Yet, empirical data quantifying century-scale changes in C or nutrients due to fire exclusion are rare. We used tree-ring reconstructions of stand structure from five ponderosa pine-dominated sites from across northern Arizona to compare live tree C, nitrogen (N), and phosphorus (P) storage between the 1880s and 1990s. Live tree biomass in the 1990s contained up to three times more C, N, and P than in 1880s. However, the increase in C storage was smaller than values used in recent U.S. C budgets. Furthermore, trees that had established prior to the 1880s accounted for a large fraction (28-66%) of the C, N, and P stored in contemporary stands. Overall, our century-scale analysis revealed that forests of the 1880s were on a trajectory to accumulate C and nutrients in trees even in the absence of fire exclusion, either because growing conditions became more favorable after the 1880s or because forests in the 1880s included age or size cohorts poised for accelerated growth. These results may lead to a reduction in the C sink attributed to fire exclusion, and they refine our understanding of reference conditions for restoration management of fire-prone forests.
authors.affiliation: Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
authors.forename: Jason P
authors.initials: JP
authors.lastname: Kaye
authors.affiliation: Department of Ecosystem Science and Management, The Pennsylvania State University, University Park, Pennsylvania, 16802, USA.
authors.forename: Margot W
authors.initials: MW
authors.lastname: Kaye
authors.affiliation: School of Natural Sciences and Sierra Nevada Research Institute, University of California, Merced, California, 95344, USA.
authors.forename: Stephen C
authors.initials: SC
authors.lastname: Hart
authors.affiliation: Ecological Restoration Institute and School of Forestry, Northern Arizona University, Flagstaff, Arizona, 86011, USA.
authors.forename: W Wallace
authors.initials: WW
authors.lastname: Covington
authors.affiliation: School of Forestry, Northern Arizona University, Flagstaff, Arizona, 86011, USA.
authors.forename: Peter Z
authors.initials: PZ
authors.lastname: Fulé
mesh_terms: D001130:Arizona; D002244:Carbon; D017753:Ecosystem; D005390:Fires; D015206:Southwestern United States; D014197:Trees
chemical_list: D002244:Carbon
keywords: Arizona; carbon; fire exclusion; nitrogen; phosphorus; ponderosa pine; tree-rings