1. Evidence of recovery of Juniperus virginiana trees from sulfur pollution after the Clean Air Act.
- Author
-
Thomas, Richard B., Spal, Scott E., Smith, Kenneth R., and Nippert, Jesse B.
- Subjects
EASTERN redcedar ,JUNIPERS ,ENVIRONMENTAL protection ,SULFUR & the environment ,AIR pollution laws ,EMISSION standards ,AIR quality - Abstract
Using dendroisotopic techniques, we show the recovery of Juniperus virginiana L. (eastern red cedar) trees in the Central Appalachian Mountains from decades of acidic pollution. Acid deposition over much of the 20th century reduced stomatal conductance of leaves, thereby increasing intrinsic water-use efficiency of the Juniperus trees. These data indicate that the stomata of Juniperus may be more sensitive to acid deposition than to increasing atmospheric CO
2 . A breakpoint in the 100-y δ13 C tree ring chronology occurred around 1980, as the legacy of sulfur dioxide emissions declined following the enactment of the Clean Air Act in 1970, indicating a gradual increase in stomatal conductance (despite rising levels of atmospheric CO2 ) and a concurrent increase in photosynthesis related to decreasing acid deposition and increasing atmospheric CO2 . Tree ring δ34 S shows a synchronous change in the sources of sulfur used at the whole-tree level that indicates a reduced anthropogenic influence. The increase in growth and the δ13 C and δ34 S trends in the tree ring chronology of these Juniperus trees provide evidence for a distinct physiological response to changes in atmospheric SO2 emissions since ∼1980 and signify the positive impacts of landmark environmental legislation to facilitate recovery of forest ecosystems from acid deposition. [ABSTRACT FROM AUTHOR]- Published
- 2013
- Full Text
- View/download PDF