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When vegetation change alters ecosystem water availability
Author(s) -
Scott Russell L.,
Huxman Travis E.,
BarronGafford Greg A.,
Darrel Jenerette G.,
Young Jessica M.,
Hamerlynck Erik P.
Publication year - 2014
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/gcb.12511
Subject(s) - environmental science , shrubland , evapotranspiration , grassland , eddy covariance , riparian zone , vegetation (pathology) , ecosystem , hydrology (agriculture) , ecosystem respiration , climate change , woodland , primary production , ecology , geology , biology , medicine , geotechnical engineering , pathology , habitat
The combined effects of vegetation and climate change on biosphere–atmosphere water vapor (H 2 O) and carbon dioxide ( CO 2 ) 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 H 2 O and CO 2 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 ( R eco ) 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 R eco 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.