Frost sensitivity of Fagus sylvatica and co-occurring deciduous tree species at exposed sites

Abstract

In Central-European forest stands on southerly to south-westerly exposed slopes of hills with shallow soil, European beech ( Fagus sylvatica L.) loses its predominance over other deciduous tree species such as oak ( Quercus spp.) or whitebeam ( Sorbus aria [L.] Cr.) due to limited availability of water. To test whether winter frost is an additional factor affecting the performance of beech at such exposed sites, we measured the minimum air temperatures between the sampling dates, and determined the frost sensitivity of F. sylvatica and of co-occurring tree species ( Quercus petraea [Matt.] Liebl., Quercus pubescens Willd., Quercus robur L., S. aria [L.] Cr.) eight times during the winter months, from October to March, at two sites in the low mountain ranges of Central Germany, which share the same climatic, topographic and edaphic conditions. At each site, two localities (stand margins and the interior of the stands) were compared. The frost sensitivity was determined in twigs of the trees using the electrolyte leakage method. Throughout the winter, frost sensitivity of F. sylvatica was higher at the stand margin than in the forest interior at one of the sites. At the other one, the frost sensitivity of S. aria was lower at the stand margin than within the stand. No consistent differences between the localities were detected in the Quercus species. Generally, the differences in frost sensitivity between the localities were only small; this was probably due to the slight differences in the minimum air temperature. Thus, it appears unlikely that, in exposed localities, the performance of the investigated tree species is limited by winter frost. More consistent differences were found among species, with F. sylvatica proving to be the most frost-sensitive, and S. aria, the least frost-sensitive species, particularly at the stand margins. The role of frost for the occurrence and performance of F. sylvatica should be further studied at the limit of its distribution along the boundary to the semihumid areas of Central Europe.