Net carbon exchange and evapotranspiration in postfire and intact sagebrush communities in the Great Basin
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Invasion of non-native annuals across the Intermountain West is causing a widespread transition from perennial sagebrush communities to fire-prone annual herbaceous communities and grasslands. To determine how this invasion affects ecosystem function, carbon and water fluxes were quantified in three, paired sagebrush and adjacent postfire communities in the northern Great Basin using a 1-m3 gas exchange chamber. Most of the plant cover in the postfire communities was invasive species including Bromus tectorum L., Agropyron cristatum (L.) Gaertn and Sisymbrium altissimum L. Instantaneous morning net carbon exchange (NCE) and evapotranspiration (ET) in native shrub plots were greater than either intershrub or postfire plots. Native sagebrush communities were net carbon sinks (mean NCE 0.2–4.3 μmol m−2 s−1) throughout the growing season. The magnitude and seasonal variation of NCE in the postfire communities were controlled by the dominant species and availability of soil moisture. Net C exchange in postfire communities dominated by perennial bunchgrasses was similar to sagebrush. However, communities dominated by annuals (cheatgrass and mustard) had significantly lower NCE than sagebrush and became net sources of carbon to the atmosphere (NCE declined to −0.5 μmol m−2 s−1) with increased severity of the summer drought. Differences in the patterns of ET led to lower surface soil moisture content and increased soil temperatures during summer in the cheatgrass-dominated community compared to the adjacent sagebrush community. Intensive measurements at one site revealed that temporal and spatial patterns of NCE and ET were correlated most closely with changes in leaf area in each community. By altering the patterns of carbon and water exchange, conversion of native sagebrush to postfire invasive communities may disrupt surface-atmosphere exchange and degrade the carbon storage capacity of these systems.
KeywordsArtemisia tridentata Bromus tectorum Invasion Carbon flux Water flux
We gratefully acknowledge G. Bollero for assistance with the experimental design and statistical analyses, S.P. Long for his guidance in calculating gas-exchange fluxes, D. Schorran for technical assistance in calibration and operation of field equipment, and E. Barrett, L. Beers, R. Bergin, C. Bowman, K. Reodica, J. Rosta, L. Sotoodeh, L. Tarnay, M. Van, H. Weatherly and B. Williams for invaluable logistical support. We thank O. Dermody, R. Knepp, A. Leakey, D. Moore, J. Tang and anonymous reviewers for thoughtful criticisms of the manuscript. This research was funded by grants from the International Arid Lands Consortium (Project 00R-05 and 02R-03), with additional support provided by the University of Illinois Graduate College and the Francis M. and Harlie M. Clark Research Support Grant.
- Anderson EW (1986) A guide for estimating cover. Rangelands 8:236–238Google Scholar
- D’Antonio CM, Vitousek PM (1992) Biological invasions by exotic grasses, the grass/fire cycle, and global change. Annu Rev Ecol Syst 23:63–87Google Scholar
- Hooper DU, Cardon ZG, Chapin III FS, Durant M (2002) Corrected calculations for soil and ecosystem measurements of CO2 flux using the LI-COR 6200 portable photosynthesis system. Oecologia, pp 1–18Google Scholar
- Kolb KJ, Sperry JS (1999) Differences in drought adaptation between subspecies of sagebrush (Artemisia tridentata). Ecology 80:2373–2384Google Scholar
- Lacey JR, Olson BE (1991) Environmental and economic impacts of noxious range weeds. In: James LF, Evans JO, Ralphs MH, Child RD (eds) noxious range weeds. Westview, San Francisco, pp 5–16Google Scholar
- Law BE, Falge E, Gu L, Baldocchi DD, Bakwin P, Berbigier P, Davis K, Hollinger D, Janssens IA, Jarvis P, Jensen NO, Katul G, Mahli Y, Matteucci G, Meyers T, Monson R, Munger W, Oechel W, Olson RA, Pilegaard K, Paw U KT, Thorgeirsson H, Valentini R, Verma S, Vesala T, Wilson K, Wofsy S (2002) Environmental controls over carbon dioxide and water vapor exchange of terrestrial vegetation. Agric For Meteorol 113:97–120CrossRefGoogle Scholar
- Link SO, Gee GW, Thiede ME, Beedlow PA (1990) Response of a shrub-steppe ecosystem to fire: Soil water and vegetational change. Arid Soil Res Rehabil 4:163–172Google Scholar
- Miller RF, Shultz LM (1987) Development and longevity of ephemeral and perennial leaves on Artemisia tridentata Nutt. ssp. wyomingensis. Great Basin Nat 47:227–230Google Scholar
- Pellant M (1994) History and Applications of the Intermountain Greenstripping Program. In: proceedings-ecology and management of annual rangelands, General Technical Report INT-GTR-313 edn. USDA Forest Service, Intermountain Research StationGoogle Scholar
- Raich JW, Schlesinger WH (1992) The global carbon dioxide flux in soil respiration and its relationship to vegetation and climate. Tellus 44B:81–89Google Scholar
- Young JA, Evans RA, Eckert RE Jr, Kay BL (1987) Cheatgrass Rangelands 9:266–270Google Scholar