Effects of fire at two frequencies on nitrogen transformations and soil chemistry in a nitrogen-enriched forest landscape

Abstract

This study reports results of the application of dormant-season prescribed fire at two frequencies (periodic (two fires in 4 years) and annual) at four southern Ohio mixed-oak (Quercus spp.) forest sites to restore the ecosystem functional properties these sites had before the onset of fire suppression and chronic atmospheric deposition. Each forest site comprised three contiguous watershed-scale treatment units: one burned in 1996 and 1999, one burned annually from 1996 through 1999, and an unburned control. Soil organic matter, available P, net N mineralization, and nitrification were not significantly changed by fire at either frequency, though values for the latter two properties increased 4-to 10-fold from the period 1995-1997 to the period 1999-2000. Fire at both frequencies resulted in increased soil pH and exchangeable Ca 2+ . Exchangeable Al 3+ was reduced by fire at two of four sites, and the molar ratio of Ca/Al was increased by fire at three of four sites. In contrast to results in most studies of fire, N transformations and availability were not increased by fire in this N-enriched region (deposition of N averaged about 6 kg·ha -1 ·year -1 over the last 20 years). We hypothesize that the large observed increase in nitrification is an indication of the onset of N saturation. Although fire appears to offset the effect of atmospheric deposition in this region by increasing soil pH, Ca 2+ , and Ca/Al ratio and reducing available Al 3+ , increased NO 3 -fluxes through the soil from continued N deposition may negate the positive effect of fire.Résumé : Cet article présente les résultats d'essais de brûlage dirigé pendant la période de dormance dans quatre stations occupées par une forêt mixte de chêne (Quercus spp.). Deux fréquences (périodique (deux fois en 4 ans) et annuelle) de brûlage dirigé ont été utilisées dans le but de restaurer les propriétés fonctionnelles de l'écosystème anté-rieures à la suppression des feux et aux dépôts atmosphériques chroniques. Chaque station forestière était constituée de trois unités correspondant à trois bassins versants contigus ayant chacun reçu un traitement : un bassin a été brûlé en 1996 et 1999, un autre a été brûlé à chaque année de 1996 à 1999 et le dernier a servi de témoin. Peu importe la fré-quence, le feu n'a pas significativement affecté la matière organique du sol, le P disponible, la minéralisation nette de N et la nitrification même si la minéralisation nette de N et la nitrification ont augmenté de 4 à 10 fois de 1995-1997 à 1999-2000. Les deux fréquences de brûlage ont entraîné une augmentation du pH du sol et de la quantité de Ca 2+ échangeable. Le feu a fait diminuer la quantité de Al 3+ échangeable dans deux des quatre stations et augmenté le rapport molaire Ca/Al dans trois des quatre stations. Contrairement à la plupart des études sur le feu, le brûlage n'a affecté ni la transformation ni la disponibilité de N dans cette région enrichie en N où les dépôts atmosphériques ont atteint en moyenne 6 kg N·ha -1 ·an -1 au cours des 20 dernières années. ...

Impacts of Fire and Fire Surrogate treatments on forest soil properties: a meta‐analytical approach

“…Increases in net N mineralization are often attributed to the alteration of organic matter by fire in such a manner as to render it more susceptible to microbial attack, to increases in microbial activity, and to changes in microclimate . However, Boerner et al (2000Boerner et al ( , 2004 quantified soil organic matter contents and net N mineralization rates in four southern Ohio mixed-oak forests subjected to annual or periodic burning and found no consistent or persistent change in any index of microbially mediated net N mineralization at the full watershed scale. In that study, pre-fire conditions and landscape characteristics were more important in explaining changes in soil C and N dynamics than was fire behavior (Boerner et al 2000).…”

Effects of repeated prescribed fires on the structure, composition, and regeneration of mixed-oak forests in Ohio

“…As studies, such as ours, are continued, we will understand more about the efficacy of using prescribed fire to sustain eastern oak forests. Our multidisciplinary study has shown that prescribed fire application can have other beneficial short-term effects, including the amelioration of acidic deposition (Boerner et al, 2004), increasing native plant diversity (Hutchinson et al, 2005), and sustaining rare plant populations (Hutchinson, 2004). hemispherical photography data.…”

Prescribed burning and understory composition in a temperate deciduous forest, Ohio, USA

“…Such fires typically remove a portion of the leaf litter and increase calcium available in the soil (Boerner et al, 2003;Hutchinson et al, 2005). Herb species richness, diversity, and cover have been shown to increase following fire in the region (Nuzzo et al, 1996;Arthur et al, 1998;Hutchinson and Sutherland, 2000;Kuddes-Fischer and Arthur, 2002).…”