title: Timing and duration of European larch growing season along altitudinal gradients in the Swiss Alps.
abstract: The 2007 European larch (Larix decidua Mill.) growing season was monitored along two elevational transects in the Lötschental valley in the Swiss Alps. Phenological observations and weekly microcore sampling of 28 larch trees were conducted between April and October 2007 at seven study sites regularly spaced from 1350 to 2150 m a.s.l. on northwest- and southeast-facing slopes. The developmental stages of nearly 75,000 individual cells assessed on 1200 thin sections were used to investigate the links between the trees' thermal regimes and growth phases including the beginning and ending of cell enlargement, wall thickening and maturation of the stem wood. Needles appeared approximately 3-4 weeks earlier than stem growth. The duration of ring formation lasted from mid-May to the end of October, with the length of the growing season decreasing along elevation from 137 to 101 days. The onset of the different growing seasons changed by 3-4 days per 100 m elevation; the ending of the growing season, however, appeared minimally related to altitude. If associated with the monitored altitudinal lapse rate of -0.5 degrees C per 100 m, these results translate into a lengthening of the growing season by approximately 7 days per degree Celsius. This study provides new data on the timing and duration of basic growth processes and contributes to quantification of the impacts of global warming on tree growth and productivity.
authors.affiliation: Institute of Geography, Climatology and Meteorology Research Group, University of Bern, Hallerstrasse 12, CH-3012 Bern, Switzerland.
authors.forename: Lea
authors.initials: L
authors.lastname: Moser
authors.forename: Patrick
authors.initials: P
authors.lastname: Fonti
authors.forename: Ulf
authors.initials: U
authors.lastname: Büntgen
authors.forename: Jan
authors.initials: J
authors.lastname: Esper
authors.forename: Jürg
authors.initials: J
authors.lastname: Luterbacher
authors.forename: Julia
authors.initials: J
authors.lastname: Franzen
authors.forename: David
authors.initials: D
authors.lastname: Frank
mesh_terms: D000531:Altitude; D002454:Cell Differentiation; D028221:Larix / Q000166:cytology* / Q000254:growth & development*; D012621:Seasons; D013557:Switzerland; D013696:Temperature