Soil and forest floor properties of silver fir and European hop hornbeam forests (Ostryo-Abietetum /Fukarek 1963/Trinajstić 1983) on Biokovo Mountain

Climate change is affecting the availability of resources and conditions critical to the life and survival of forest communities and the species that inhabit them, especially at the edges of their distribution. Numerous studies indicate that fir forests are threatened by climate change, especially at the southern edges of their range where the negative effects of warming are more pronounced. The aim of this study was to determine for the first time the soil and forest floor properties in thermophilic, southernmost fir forests (Ostryo-Abietetum /Fukarek 1963/ Trinajstić 1983) in Croatia. These forests grow from 850 m to 1150 m a.s.l. on the continental slope of Biokovo Mountain on a characteristic sinkhole relief, which influences the mosaic arrangement of the soil, vegetation and forest floor. At the bottom of the sinkholes, fir trees dominate, rockiness is less pronounced and Mollic Leptosol and Leptic Cambisol alternate. The forest floor mass (load) is higher. On the other hand, at the edges of the sinkholes, rockiness is more pronounced, the soil is either very shallow (Mollic Leptosol) or absent, and the forest floor mass is lower. Thermophilic tree species dominate, while firs are sporadic or absent. The determined soil and forest floor properties were compared with those of other fir communities in Croatia. In a number of sinkholes, it was found that in summer (the dry and hot period) cold air flows in from caves and cracks, creating specific microclimatic conditions in sinkholes that are favourable for fir and could be a key factor for its survival.