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Abstract Carbon flux in arid and semiarid area shrublands, especially in old‐growth shrub ecosystems, has been rarely studied using eddy covariance techniques. In this study, eddy covariance measurements over a 100‐year old‐growth chamise‐dominated chaparral shrub ecosystem were conducted for 7 years from 1996 to 2003. A carbon sink, from −96 to −155 g C m −2 yr −1 , was determined under normal weather conditions, while a weak sink of −18 g C m −2 yr −1 and a strong source of 207 g C m −2 yr −1 were observed as a consequence of a severe drought. The annual sink strength of carbon in the 7‐year measurement period was −52 g C m −2 yr −1 . The results from our study indicate that, in contrast to previous thought, the old‐growth chaparral shrub ecosystem can be a significant sink of carbon under normal weather conditions and, therefore, be an important component of the global carbon budget.
Luo et al. (Wed,) studied this question.