Research PapersCarbon Fluxes on North American Rangelands
Section snippets
INTRODUCTION
There is considerable interest in potential effects of increasing atmospheric carbon dioxide (CO2) on global climate, and consequently in maximizing terrestrial and oceanic sinks for carbon (C) as a means of ameliorating negative impacts. Attempts to balance known sources and sinks of the global C cycle often result in a “missing sink” of 1.3 Gt C · yr−1 to 1.4 Gt C · yr−1 (Woodwell et al. 1998). Carbon sequestration by terrestrial ecosystems may account for a portion of the missing C, although
Study Sites
Eight individual sites were used in this study. Specific location, vegetation type, dominant species, and general site characteristics are presented in Tables 1 and 2. The sites were selected to represent native rangeland in the area. All sites were considered to be in good ecological condition (based on species composition) and were not managed (grazed by livestock, burned, or fertilized) during the course of the study. The one exception was the tallgrass prairie in Temple, Texas, which was
RESULTS AND DISCUSSION
Five of the eight rangeland sites that we studied typically functioned as sinks for atmospheric CO2 during the study period, but sink strength varied among biomes and years (Table 6). The sagebrush steppe sites in the northwestern United States were surprisingly strong sinks for C during the study period (Fig. 1; Table 6). Grassland sites on the US Great Plains were variable, with most sites either weak or moderate sinks for atmospheric CO2 (Figs. 2 and 3; Table 6). In the sagebrush steppe,
MANAGEMENT IMPLICATIONS
Although we did not test the impact of management practices on rangeland NEE, there are some important points to be gleaned from the annual NEE patterns. Because NEE and vegetation productivity are linked, these patterns have implications for managing rangelands. Most of the sites exhibited rapid CO2 uptake for a short period (2 mo to 4 mo) and a longer period of low CO2 loss (where ecosystem respiration exceeded photosynthesis). Drought reduced the period and magnitude of positive NEE.
ACKNOWLEDGMENTS
The authors wish to thank the many individuals who provided technical and administrative support to this project. We also thank Joel Brown, Wayne Polley, several anonymous reviewers, and Associate Editor Robert Nowak for comments that improved the manuscript.
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Authors are listed in alphabetical order after senior author.