The delta C-13 of tree rings in full-bark and strip-bark bristlecone pine trees in the White Mountains of California

Dendrochronological work at Sheep Mountain in the White Mountains, CA has d emonstrated that bristlecone pine trees in two forms, full-bark and strip-b ark, have experienced different cambial growth rates over the past century or longer. The strip-bark trees showed a greater growth increase than the f ull-bark ones. A calculation of the plant water-use efficiency (W) in respo nse to anthropogenic CO2 released into the atmosphere shows that W of trees in both forms has increased for the past 200 years. However, there is no s ignificant difference between the two tree forms in the rate of increase in W. This implies at least two possibilities with respect to the CO2 fertili zation effect. First, the biomass in both tree forms might have increased, but carbon distribution among different parts of a tree was different. Seco nd, the biomass may increase without causing any corresponding change in th e plant water-use efficiency.