Soil Nitrogen Transformations Under Alternative Management Strategies in Appalachian Forests

Abstract

Once subject to frequent fi re and strongly N limited, the forests of the Appalachian Mountain region of eastern North America have experienced almost a century of fi re suppression, and changes in tree species composition, understory density and composition, and accumulations of detritus have paralleled the changes in fi re frequency. In an effort to restore these ecosystems and reduce wildfi re hazard, alternative management strategies (prescribed fi re, mechanical fuel reduction, and a combination of both) were implemented at study sites in Ohio and North Carolina as part of the Fire and Fire Surrogate Network Study. As changes in N cycling resulting from these treatments could have potential negative impacts on forest health that might limit their usefulness as management alternatives, we monitored treatment effects on extractable total inorganic N (TIN), net N mineralization, net nitrifi cation, and proportional nitrifi cation during the growing season before treatment, the fi rst growing season after treatment, and the third or fourth growing season after treatment. Mechanical treatment resulted in increases in extractable TIN, N mineralization, and nitrifi cation during the fi rst post-treatment year in Ohio and TIN was greater in the mechanical treatment and the mechanical + fi re treatment during the third post-treatment year in North Carolina. Net N mineralization was reduced by fi re alone in Ohio, but not in North Carolina. Nitrogen transformation rates were 2-to 10-fold higher in Ohio than North Carolina, a difference that may partly result from of the ericaceous shrub understory present in North Carolina but not in Ohio. Impacts of these treatments on N transformations were modest and for the most part transient, and would therefore not eliminate these treatments as viable management strategies for wildfi re hazard reduction or ecosystem restoration.Abbreviations: FFS, Fire and Fire Surrogate; IMI, integrated moisture index; LEC, landscape ecological classifi cation system; TIN, total inorganic nitrogen.

A meta-analysis on the response of microbial biomass, dissolved organic matter, respiration, and N mineralization in mineral soil to fire in forest ecosystems

“…As expected, fire had significant negative impacts overall on soil respiration and N mineralization. Consistent with the results of the current study, many previous studies also noted that fire decreased soil C and N mineralization (Choromanska and DeLuca, 2001;Coates et al, 2008;Hamman et al, 2008;Antunes et al, 2009). The decrease in soil organic C and the increase in recalcitrant materials likely caused the decrease in C and N mineralization.…”

Restoration of shortleaf pine (Pinus echinata)-hardwood ecosystems severely impacted by the southern pine beetle (Dendroctonus frontalis)

“…Some studies have reported no response or a transient increase in plant available nutrients following prescribed fire in mixed-hardwood forests in Appalachian forests Boerner et al, 2000Boerner et al, , 2004Hubbard et al, 2004;Coates et al, 2008). Others have reported significant increases in available nutrients following burning Boerner and Brinkman, 2005).…”

Evaluating forest biomass utilization in the Appalachians: A review of potential impacts and guidelines for management

“…They found that the already high rates of N mineralization were increased significantly by whole-tree harvest treatments, and the addition of N, Ca, and Mg fertilization with whole-tree harvesting resulted in the highest rates of nitrification. Coates et al (2008) showed that mechanical thinningfrom-below treatments resulted in increases in extractable total inorganic N, net N mineralization, and nitrification during the first post-treatment year. Elevated leaching of Ca and Mg often occurs with increased nitrification.…”