Radial growth of Pinus sylvestris growing on alluvial terraces is sensitive to water-level fluctuations.

Along the Alpine river Lech (Tyrol, Austria), poorly grown Scots pine (Pinus sylvestris) stands dominate on dry alluvial terraces, which are made up of coarse calcareous gravel. Here we evaluated the impact of environmental factors, such as precipitation, temperature and water table, on annual variability of radial growth. Tree-ring chronologies from six stands comprising different age classes were developed by extracting two core samples from more than 15 trees per plot. Pearson correlations were applied to determine the influence of environmental factors. Close inverse correlations (r2 > 0.35) between maximum water table during the growing period and annual increments of adult stands indicated that water surplus in the rooting zone was the primary growth-limiting factor. Drought stress reduced growth only in some extremely dry years. Results provide evidence that dominance of P. sylvestris on gravelly alluvial terraces is caused not only by tolerance of soil dryness and nutrient deficiency, as previously assumed, but also by a dynamic multilayered root system which allows adaptation to highly variable soil-moisture conditions.