title: Radial growth rate increases in naturally occurring ponderosa pine trees: a late-20th century CO2 fertilization effect?
abstract: The primary objective of this study was to determine if gradually increasing levels of atmospheric CO2, as opposed to 'step' increases commonly employed in controlled studies, have a positive impact on radial growth rates of ponderosa pine (Pinus ponderosa) in natural environments, and to determine the spatial extent and variability of this growth enhancement. We developed a series of tree-ring chronologies from minimally disturbed sites across a spectrum of environmental conditions. A series of difference of means tests were used to compare radial growth post-1950, when the impacts of rising atmospheric CO2 are best expressed, with that pre-1950. Spearman's correlation was used to relate site stress to growth-rate changes. Significant increases in radial growth rates occurred post-1950, especially during drought years, with the greatest increases generally found at the most water-limited sites. Site harshness is positively related to enhanced radial growth rates. Atmospheric CO2 fertilization is probably operative, having a positive effect on radial growth rates of ponderosa pine through increasing water-use efficiency. A CO2-driven growth enhancement may affect ponderosa pine growing under both natural and controlled conditions.
authors.affiliation: Department of Geography and Planning, Appalachian State University, Boone, NC 28608, USA. soulept@appstate.edu
authors.forename: Peter T
authors.initials: PT
authors.lastname: Soulé
authors.forename: Paul A
authors.initials: PA
authors.lastname: Knapp
mesh_terms: D001272:Atmosphere / Q000737:chemistry*; D002140:California; D002245:Carbon Dioxide / Q000502:physiology*; D005308:Fertilizers; D009922:Oregon; D041604:Pinus ponderosa / Q000254:growth & development*; D014867:Water / Q000502:physiology
chemical_list: D005308:Fertilizers; D014867:Water; D002245:Carbon Dioxide