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Tree growth response to drought and temperature in a mountain landscape in northern Arizona, USA


Thomas Kolb, School of Forestry, Northern Arizona University, Flagstaff, AZ 86011-5018, USA.


Aim  To understand how tree growth response to regional drought and temperature varies between tree species, elevations and forest types in a mountain landscape.

Location  Twenty-one sites on an elevation gradient of 1500 m on the San Francisco Peaks, northern Arizona, USA.

Methods  Tree-ring data for the years 1950–2000 for eight tree species (Abies lasiocarpa var. arizonica (Merriam) Lemm., Picea engelmannii Parry ex Engelm., Pinus aristata Engelm., Pinus edulis Engelm., Pinus flexilis James, Pinus ponderosa Dougl. ex Laws., Pseudotsuga menziesii var. glauca (Beissn.) Franco and Quercus gambelii Nutt.) were used to compare sensitivity of radial growth to regional drought and temperature among co-occurring species at the same site, and between sites that differed in elevation and species composition.

Results  For Picea engelmannii, Pinus flexilis, Pinus ponderosa and Pseudotsuga menziesii, trees in drier, low-elevation stands generally had greater sensitivity of radial growth to regional drought than trees of the same species in wetter, high-elevation stands. Species low in their elevational range had greater drought sensitivity than co-occurring species high in their elevational range at the pinyon-juniper/ponderosa pine forest ecotone, ponderosa pine/mixed conifer forest ecotone and high-elevation invaded meadows, but not at the mixed conifer/subalpine forest ecotone. Sensitivity of radial growth to regional drought was greater at drier, low-elevation compared with wetter, high-elevation forests. Yearly growth was positively correlated with measures of regional water availability at all sites, except high-elevation invaded meadows where growth was weakly correlated with all climatic factors. Yearly growth in high-elevation forests up to 3300 m a.s.l. was more strongly correlated with water availability than temperature.

Main conclusions  Severe regional drought reduced growth of all dominant tree species over a gradient of precipitation and temperature represented by a 1500-m change in elevation, but response to drought varied between species and stands. Growth was reduced the most in drier, low-elevation forests and in species growing low in their elevational range in ecotones, and the least for trees that had recently invaded high-elevation meadows. Constraints on tree growth from drought and high temperature are important for high-elevation subalpine forests located near the southern-most range of the dominant species.

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