When vegetation change alters ecosystem water availability

Russell L. Scott, Travis E. Huxman, Greg A. Barron-Gafford, G. Darrel Jenerette, Jessica M. Young, Erik P. Hamerlynck

Research output: Contribution to journalArticle

37 Scopus citations

Abstract

The combined effects of vegetation and climate change on biosphere-atmosphere water vapor (H2O) and carbon dioxide (CO2) exchanges are expected to vary depending, in part, on how biotic activity is controlled by and alters water availability. This is particularly important when a change in ecosystem composition alters the fractional covers of bare soil, grass, and woody plants so as to influence the accessibility of shallower vs. deeper soil water pools. To study this, we compared 5 years of eddy covariance measurements of H2O and CO2 fluxes over a riparian grassland, shrubland, and woodland. In comparison with the surrounding upland region, groundwater access at the riparian sites increased net carbon uptake (NEP) and evapotranspiration (ET), which were sustained over more of the year. Among the sites, the grassland used less of the stable groundwater resource, and increasing woody plant density decoupled NEP and ET from incident precipitation (P), resulting in greater exchange rates that were less variable year to year. Despite similar gross patterns, how groundwater accessibility affected NEP was more complex than ET. The grassland had higher respiration (Reco) costs. Thus, while it had similar ET and gross carbon uptake (GEP) to the shrubland, grassland NEP was substantially less. Also, grassland carbon fluxes were more variable due to occasional flooding at the site, which both stimulated and inhibited NEP depending upon phenology. Woodland NEP was large, but surprisingly similar to the less mature, sparse shrubland, even while having much greater GEP. Woodland Reco was greater than the shrubland and responded strongly and positively to P, which resulted in a surprising negative NEP response to P. This is likely due to the large accumulation of carbon aboveground and in the surface soil. These long-term observations support the strong role that water accessibility can play when determining the consequences of ecosystem vegetation change.

Original languageEnglish (US)
Pages (from-to)2198-2210
Number of pages13
JournalGlobal change biology
Volume20
Issue number7
DOIs
StatePublished - Jul 2014

    Fingerprint

Keywords

  • Carbon dioxide
  • Ecosystem water-use
  • Eddy covariance
  • Evapotranspiration
  • Mesquite (Prosopis velutina)
  • Net ecosystem production
  • Riparian
  • Sacaton semiarid (Sporobolus wrightii)
  • Vegetation change
  • Water-use efficiency
  • Woody plant encroachment

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

Cite this

Scott, R. L., Huxman, T. E., Barron-Gafford, G. A., Darrel Jenerette, G., Young, J. M., & Hamerlynck, E. P. (2014). When vegetation change alters ecosystem water availability. Global change biology, 20(7), 2198-2210. https://doi.org/10.1111/gcb.12511