Radial growth response of coniferous forest trees in an inner Alpine environment to heat-wave in 2003

The record-breaking heat-wave in summer 2003 was expected to have a strong impact on tree growth, especially where trees occur at their ecological limits. We studied radial growth response of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) exposed to dry inner Alpine climate (Tyrol, Austria) to extreme hot and dry conditions in 2003. Tree ring chronologies from two stands comprising different social status, i.e. dominant, co-dominant and suppressed trees, on a south- and north-facing slope, which represent xeric and dry-mesic site conditions, respectively, were analysed. Growth–climate relationships were explored using response function analysis and Pearson correlation coefficients. Major findings of our study were: (i) radial growth in 2003 was strongest reduced in suppressed P. sylvestris growing on a xeric site and in dominant Picea abies growing on the dry-mesic site, (ii) median reductions in annual increments reached 35% compared to previous years (1998–2002) and were caused by early stop of cambial activity as indicated by pronounced decrease in latewood width and (iii) April through June precipitation was the environmental factor most strongly associated with growth of both species. Ring width of P. sylvestris and Picea abies was additionally limited by hot late spring and hot late spring/summer months, respectively. The minor impact of the 2003 summer heat-wave on growth of drought exposed forest trees might find its explanation in strong dependency of radial stem growth on precipitation during late spring and preconditioning of tree vigor in previous years. Results demonstrate that impact of climate extremes on radial tree growth can vary within site and canopy position and strongly depend on species-specific response to climate factors.