Wind Resistance of Eastern Baltic Silver Birch (Betula pendula Roth.) Suggests Its Suitability for Periodically Waterlogged Sites

Abstract

Storms and wind damage are the main cause of biomass loss in forests of Northern Europe, as well as they are synergic with the disturbances causing intense water and temperature stress. This highlights the necessity for climate-smart management at landscape level coupling ecological demands of forestry species with their wind resistance. Silver birch (Betula pendula Roth.), which is highly plastic species, appears to be promising for a wider application under such conditions, as it is believed to tolerate wide range of weather conditions. Though silver birch can be sensitive to water deficit and windthrow, local information on its wind tolerance in sites with different moisture regimes is advantageous. Mechanical stability of 71 mid-aged silver birches (Betula pendula Roth.) growing in seven dry (Hylocomiosa) and five periodically waterlogged (Myrtilloso-sphagnosa) sites with mineral soils in Latvia (hemiboreal lowland conditions) were assessed by the destructive static pulling tests. Site type had a significant, yet intermediate effect on the stability of silver birch. As expected, trees under periodically waterlogged conditions were more prone to collapse under static loading, however, they showed a better resistance to primary failure (beginning of wood structure deformation). Uprooting was the most common form of tree collapse. Surprisingly, considering similar root depths, stem breakage was more frequent in the periodically waterlogged than dry sites (21.9 vs. 5.1%, respectively), indicating high loading resistance of roots, supporting high plasticity and wind resistance of the studied metapopulation of silver birch. Nevertheless, in the periodically waterlogged sites, the difference between forces needed to cause primary and secondary (collapse) failures of stem decreased with age/size, implying necessity for optimization of rotation length. Accordingly, quantification of wind resistance can aid climate-smart selection of species for forest regeneration depending on landscape, suggesting birch as wind resistant option under periodically waterlogged conditions.