title: Drought responses of conifers in ecotone forests of northern Arizona: tree ring growth and leaf delta13C.
abstract: We sought to understand differences in tree response to meteorological drought among species and soil types at two ecotone forests in northern Arizona, the pinyon-juniper woodland/ponderosa pine ecotone, and the higher elevation, wetter, ponderosa pine/mixed conifer ecotone. We used two approaches that provide different information about drought response: the ratio of standardized radial growth in wet years to dry years (W:D) for the period between years 1950 and 2000 as a measure of growth response to drought, and delta13C in leaves formed in non-drought (2001) and drought (2002) years as a measure of change in water use efficiency (WUE) in response to drought. W:D and leaf delta13C response to drought for Pinus edulis and P. ponderosa did not differ for trees growing on coarse-texture soils derived from cinders compared with finer textured soils derived from flow basalts or sedimentary rocks. P. ponderosa growing near its low elevation range limit at the pinyon-juniper woodland/ponderosa pine ecotone had a greater growth response to drought (higher W:D) and a larger increase in WUE in response to drought than co-occurring P. edulis growing near its high elevation range limit. P. flexilis and Pseudotsuga menziesii growing near their low elevation range limit at the ponderosa pine/mixed conifer ecotone had a larger growth response to drought than co-occurring P. ponderosa growing near its high elevation range limit. Increases in WUE in response to drought were similar for all species at the ponderosa pine/mixed conifer ecotone. Low elevation populations of P. ponderosa had greater growth response to drought than high-elevation populations, whereas populations had a similar increase in WUE in response to drought. Our findings of different responses to drought among co-occurring tree species and between low- and high-elevation populations are interpreted in the context of drought impacts on montane coniferous forests of the southwestern USA.
authors.affiliation: School of Forestry, Northern Arizona University, Flagstaff, AZ, 86011-5018, USA.
authors.forename: Henry D
authors.initials: HD
authors.lastname: Adams
authors.forename: Thomas E
authors.initials: TE
authors.lastname: Kolb
mesh_terms: D001130:Arizona; D002247:Carbon Isotopes / Q000032:analysis*; D004190:Disasters; D008137:Longitudinal Studies; D028223:Pinus / Q000254:growth & development*; D018515:Plant Leaves / Q000737:chemistry*; D012987:Soil / Q000032:analysis; D013045:Species Specificity; D014197:Trees
chemical_list: D002247:Carbon Isotopes; D012987:Soil