Law, B. E.; Goldstein, A. H.; Anthoni, P. M.; Unsworth, M. H.; Panek, J. A.; Bauer, M. R.; Fracheboud, J. M.; Hultman, N. 2001. Carbon dioxide and water vapor exchange by young and old ponderosa pine ecosystems during a dry summer. Tree Physiology. 21: 299-308.