Minor European broadleaved tree species are more drought-tolerant than Fagus sylvatica but not more tolerant than Quercus petraea

More frequent and intensive droughts are projected to affect the vitality of major European tree species. Therefore, it is important to search for alternative, more drought-tolerant species to ensure ecological stability, biodiversity, and productivity of forests in future. Based on their relative abundance at very dry and warm sites, the otherwise rare and little-known, minor broadleaved species like Sorbus torminalis, S. domestica, Acer cam-pestre, and A. platanoides are thought to be drought-tolerant. However, there is so far only limited scientific evidence to support that notion. Here we quantified the effect of extreme droughts (1947, 1976, and 2003) on radial growth of mature trees of the minor broadleaves in relation to the common companion species Quercus petraea and Fagus sylvatica in southwest Germany. Based on tree-ring analyses with a commensurate sample size for such rare species, the ability to resist and recover from drought, as well as the medium-term resilience of mature trees was studied. Likewise, the sensitivity of the species to temperature and precipitation was assessed. Radial growth was positively related to spring and summer precipitation for all species, whereas high summer temperatures led to decreased growth rates for A. platanoides, S. domestica, and F. sylvatica. Whereas S. torminalis appeared to be resistant and resilient in relation to drought, S. domestica and A. platanoides were also resilient but less resistant to drought stress. A synoptic ranking of the drought tolerance of all tree species suggests that the minor broadleaved tree species are not more drought-tolerant than Q. petraea, except for A. campestre. We conclude that cultivation of these minor species as well as Q. petraea should be expanded on xerix sites, where F. sylvatica reaches its growth limits.