Journal Article

Effect of irrigation on needle morphology, shoot and stem growth in a drought-exposed <i>Pinus sylvestris</i> forest

Matthias Dobbertin, Britta Eilmann, Peter Bleuler, Arnaud Giuggiola, Elisabeth Graf Pannatier, Werner Landolt, Patrick Schleppi and Andreas Rigling

in Tree Physiology

Volume 30, issue 3, pages 346-360
Published in print March 2010 | ISSN: 0829-318X
Published online January 2010 | e-ISSN: 1758-4469 | DOI:
Effect of irrigation on needle morphology, shoot and stem growth in a drought-exposed Pinus sylvestris forest

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In Valais, Switzerland, Scots pines (Pinus sylvestris L.) are declining, mainly following drought. To assess the impact of drought on tree growth and survival, an irrigation experiment was initiated in 2003 in a mature pine forest, approximately doubling the annual precipitation. Tree crown transparency (lack of foliage) and leaf area index (LAI) were annually assessed. Seven irrigated and six control trees were felled in 2006, and needles, stem discs and branches were taken for growth analysis. Irrigation in 2004 and 2005, both with below-average precipitation, increased needle size, area and mass, stem growth and, with a 1-year delay, shoot length. This led to a relative decrease in tree crown transparency (−14%) and to an increase in stand LAI (+20%). Irrigation increased needle length by 70%, shoot length by 100% and ring width by 120%, regardless of crown transparency. Crown transparency correlated positively with mean needle size, shoot length and ring width and negatively with specific leaf area. Trees with high crown transparency (low growth, short needles) experienced similar increases in needle mass and growth with irrigation than trees with low transparency (high growth, long needles), indicating that seemingly declining trees were able to ‘recover’ when water supply became sufficient. A simple drought index before and during the irrigation explained most of the variation found in the parameters for both irrigated and control trees.

Keywords: leaf area index; needle size; ring width; Scots pine; shoot length

Journal Article.  8458 words.  Illustrated.

Subjects: Plant Sciences and Forestry

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