Soil responses to management, increased precipitation, and added nitrogen in ponderosa pine forests

Bruce A. Hungate, Stephen C. Hart, Paul C. Selmants, Sarah I. Boyle, Catherine A. Gehring

Research output: Contribution to journalArticle

20 Scopus citations

Abstract

Forest management, climatic change, and atmospheric N deposition can affect soil biogeochemistry, but their combined effects are not well understood. We examined the effects of water and N amendments and forest thinning and burning on soil N pools and fluxes in ponderosa pine forests near Flagstaff, Arizona (USA). Using a 15N-depleted fertilizer, we also documented the distribution of added N into soil N pools. Because thinning and burning can increase soil water content and N availability, we hypothesized that these changes would alleviate water and N limitation of soil processes, causing smaller responses to added N and water in the restored stand. We found little support for this hypothesis. Responses of fine root biomass, potential net N mineralization, and the soil microbial N to water and N amendments were mostly unaffected by stand management. Most of the soil processes we examined were limited by N and water, and the increased N and soil water availability caused by forest restoration was insufficient to alleviate these limitations. For example, N addition caused a larger increase in potential net nitrification in the restored stand, and at a given level of soil N availability, N addition had a larger effect on soil microbial N in the restored stand. Possibly, forest restoration increased the availability of some other limiting resource, amplifying responses to added N and water. Tracer N recoveries in roots and in the forest floor were lower in the restored stand. Natural abundance δ15N of labile soil N pools were higher in the restored stand, consistent with a more open N cycle. We conclude that thinning and burning open up the N cycle, at least in the short term, and that these changes are amplified by enhanced precipitation and N additions. Our results suggest that thinning and burning in ponderosa pine forests will not increase their resistance to changes in soil N dynamics resulting from increased atmospheric N deposition or increased precipitation due to climatic change. Restoration plans should consider the potential impact on long-term forest productivity of greater Nlosses from a more open N cycle, especially during the period immediately after thinning and burning.

Original languageEnglish (US)
Pages (from-to)1352-1365
Number of pages14
JournalEcological Applications
Volume17
Issue number5
DOIs
StatePublished - Jul 1 2007

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Keywords

  • Climatic change
  • Forest restoration
  • Microbial biomass
  • N isotope tracer
  • Nitrification
  • Nitrogen fertilization
  • Nitrogen mineralization
  • Precipitation
  • δ N

ASJC Scopus subject areas

  • Ecology

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