Climate response in dominant and suppressed spruce trees, Picea abies (L.)Karst., on a subalpine and lower montane site in Switzerland

In most dendroclimatological reconstructions, cores are usually taken from the biggest and oldest trees in a stand. The objective of the present study was to investigate the possible influence of such a subjective sampling te chnique in climate reconstructions using tree ring data. In order to assess the implications of any influence, the study was carried out in two stands with different site elevations and different climate data was used for one of the sites. Twenty-seven spruce trees from an upper timberline site and 18 spruce trees from a lower montane site were investigated. On both sites, subsets of nine doininant and nine suppressed trees were established on th e basis of social status and stem diameter. Four additional subsets were ma de up of trees from the timberline site. The subsets ''winner", "loser" and "indifferent" were based on cumulative basal increment growth, and the sub set "damaged" only; contained trees with strong stem wood injuries. The cli mate response of each subset was calculated using bootstrap response functi ons over the investigation period 1901-1995. Mean monthly temperature and m onthly precipitation sums were used as independent variables. For the subal pine site, response function models with measured and modelled climate data were calculated. On the subalpine site, the results indicate significant p ositive correlation of tree-ring growth to monthly mean temperatures in lun e (r = 0.294) and July (r = 0.305), and on the lower montane site, signific ant negative correlation to June temperatures (r = -0.234). Shifts in the c orrelation values of single months between the subsets as well as between t he models with measured and modelled climate data series were small. The la rgest difference in the tree-ring growth - climate relationship was found b etween the subalpine: and lower montane sites. The results reveal that the common sampling strategy in dendroclimotology (oldest, largest and dominant trees) hardly affects the results in annual climate response. The results also confirm that ecological site conditions are the most determining facto rs in the growth models. The selection of meteorological stations can also affect the results but this is of secondary importance. The social status o f the toe is of less importance for tree ring growth compared to site eleva tion and the weather stations used for the regression model. Thus, restrict ing sampling to the biggest and oldest trees does not seem to be a major pr oblem for dendroclimatological reconstructions.