Fire can alter a multitude of ecosystem properties that have the potential to affect rates of litter decomposition and nitrogen dynamics. In this study, we examined the effect of long-term variation in fire frequency in Minnesota oak savanna on rates of litter mass loss of a common tree species (Quercus ellipsoidalis) to determine how site and intraspecific litter characteristics impacted by variation in fire frequency affect rates of decomposition, litter N dynamics, and litter microbial biomass. Although an increase in fire frequency resulted in higher litter temperatures, lower litter moisture, and decreased soil N and P availability, site characteristics had no net effect on rates of mass loss. Rather, litter C:N ratio, which increased with increased fire frequency, was the dominant predictor of rates of decomposition and litter N dynamics. Increased litter C:N led to decreased rates of decomposition and N immobilization, regardless of the characteristics of the site of decomposition. Therefore, it is the indirect effects of long-term variation in fire frequency on litter characteristics rather than fire's direct effects on site characteristics that determine fire effects on decomposition and N dynamics in this system. Slower rates of decomposition and increased N immobilization of litter produced in frequently burned sites may enhance fire-induced N losses, further decelerating rates of N cycling in frequently burned sites.
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Acknowledgments The authors would like to acknowledge P. Reich, J. Powers, L. Kinkel, J. Pastor, and two anonymous reviewers for helpful comments on this manuscript. Megan Ogdahl provided invaluable assistance in the Weld and laboratory. Funding was provided by the National Science Foundation (DEB-0080382 and DEB-9977047). Experiments in this paper comply with the current laws of the country in which they were performed.
Copyright 2009 Elsevier B.V., All rights reserved.
- Mass loss
- Microbial biomass
- Nitrogen immobilization
- Oak savanna
- Quercus ellipsoidalis