title: Cambial activity and xylem cell development inPinus cembraandPinus sylvestrisat their climatic limits in the Eastern Alps in 2007.
abstract: It has been frequently stressed that at distributional boundaries, like at the Alpine timberline and within dry inner Alpine environments, tree growth will be affected first by changing climate conditions. Climate in 2007 was characterized by the occurrence of exceptionally mild temperatures in spring (3.4 and 2.7 °C above long-term mean (LTM) at timberline and the valley sites, respectively) with an almost continuous drought period recorded in April and slightly warmer than average temperatures throughout summer (1.3 °C above LTM at both sites). We compared temporal dynamics of cambial activity and xylem cell development inPinus cembraat the Alpine timberline (1950 m a.s.l.) andPinus sylvestrisat a xeric inner Alpine site (750 m a.s.l.) by repeated cellular analyses of micro-cores (n = 5 trees/site). While onset of wood formation inP. sylvestrisandP. cembradiffered by about two weeks (12 and 27 April, respectively), maximum daily growth rates peaked on 6 May at the valley site and on 23 June at timberline. At both sites maximum tracheid production was reached prior to occurrence of more favourable climatic conditions during summer, i.e. an increase in precipitation and temperature. Xylem formation ended on 31 August and 28 October at the xeric site and at timberline, respectively. This study demonstrates the plasticity of tree-ring formation along an altitudinal transect in response to water availability and temperature. Whether early achievement of maximum growth rates is an adaptation to cope with extreme environmental conditions prevailing at limits of tree growth needs to be analysed more closely by taking belowground carbon allocation into account.
authors.affiliation: Institut für Botanik, Leopold-Franzens-Universität Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria.
authors.forename: Irene
authors.initials: I
authors.lastname: Swidrak
authors.forename: Andreas
authors.initials: A
authors.lastname: Gruber
authors.forename: Walter
authors.initials: W
authors.lastname: Oberhuber
keywords: Alpine timberline; Scots pine; Stone pine; cambium; dry inner Alpine valley; intra-annual growth; wood anatomy; xylogenesis