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ŠUMARSKI LIST 11-12/2012 str. 26     <-- 26 -->        PDF

Gorski kotar and Lika, we established that in the area of Učka Nature Park the following plant associations of beech forests occure: Seslerio autumnali-Fagetum M. Wraber ex Borhidi 1963, Seslerio autumnali-Fagetum allietosum ursinii subass. nova hoc loco, Ranunculo platanifoliae-Fagetum Marinček et al. 1993.
Seslerio autumnali-Fagetum is widely distributed across investigated area and forms a continuous vegetation belt from 800 to 1150 m. Here it occurs on all aspects and slopes. On lower altitudes (700–800 m) it occurs in separate stands on mesophilous habitats (ditches, karst depressions) surrounded by vegetation of Ostryo-Carpinion. Moreover, it is present in separate stands on altitudes up to 1350 m, on thermophilous habitats within ass. Ranunculo platanifoliae-Fagetum.
They are typical stands of this association characterized by a large number of thermophilic species (Sesleria autumnalis, Ostrya carpinifolia, Sorbus aria, Acer obtusatum, Cornus mas etc.) but still with significant number of mesophilic species of beech forests such as – Acer pseudoplatanus, Daphne mezereum, Corylus avellana, Lonicera xylosteum, Cardamine enneaphyllos, C. bulbifera, Aremonia agriomonoides, Anemone nemorosa, Euphorbia amygdaloides (Trinajstić 1996, 2008; Vukelić et al. 2008).
As opposed to stands of this association on other areas (Trinajstić 1996; Dakskobler 1990, 1996, 1997), stands from the investigated area are characterized by smaller number of species (26,1 on average). The primary reason for this is great abundance of Sesleria autumnalis which prevents the growth of other species. Furthermore forests of Učka and Ćićarija occure in a broad and continuous complex and the influence of neighboring vegetation types is weaker. On other areas this plant community often occurs in a narrow zone or is intermittent by other vegetation types, therefore species from neighbouring vegetation types to some extent enter in its floristic composition (Vukelić et al. 2008).
Some relevés of this association have significantly higher number and abundancy of thermophilic species such as Ostrya carpinifolia, Acer obtusatum, Sorbus aria, Tanacetum corymbosum, etc. These stands usually occure on lower altitudes, they have more open tree layer cover with higher average EIV values for temperature, light and soil reaction. They have developed due succession of ass. Seslerio-Ostryetum. It is a secondary association which has occupied large areas in the past. In the last decades on the area of Istria there have been great changes in management practices (absence of pasture and mowing) and different migration changes resulting in the secondary succession towards Seslerio-Fagetum or Ostryo-Quercetum pubescentis, depending on the habitat (Šugar 1992; Čarni 1999; Marinček and Čarni 2002; Trinajstić 2008). On such areas by termination of management activities tree layer cover gradually closes, which creates mesophilous conditions for occurrence of beech and progressively other mesophilous species of beech forests.
In the southernmost part of the Učka Nature Park (locality Bukovo) on a very small area specific stands of beech forest are developed surrounded by the thermophilous vegetation of Ostryo-Carpinion. This is a ditch protected from the sea by high ridge. These beech stands are situated on altitudes from 500 m up to 720 m. According to average EIV values these are the warmest habitats of beech forests in the investigated area with high moisture and nutrient content. Such specific habitat features as well as proximity of Ostryo-Carpinion vegetation lead to interesting combination of thermophilous (Ostryo-Carpinion) and mesophilous (Lamio orvalae-Fagenion) species. As a result of all the above-mentioned, a new subassociation is described (Seslerio autumnali-Fagetum allietosum ursinii subass. nova hoc loco). It is characterized by presence and high coverage of mesophilous differential species – Allium ursinum, Daphne laureola, Corydalis cava, Ilex aquifolium and Leucojum vernum. Besides, it differs by high coverage of other mesophilous species such as – Lamium orvala, Erytronium dens-canis, Mercurialis perennis and others. Sesleria autumnalis as well as some other thermophilous species (Ostrya carpinifolia, Fraxinus ornus, Cornus mas and Acer obtusatum) acts as a connection towards the typical association.
Ass. Ranunculo platanifolii-Fagetum is developed in the highest parts of the Park. On Vojak it forms more or less compact complex intermittent by patches of ass. Seslerio-Fagetum on thermophilous microlocalities, while on other sites it occurs in isolated stands with more humid and colder microclimate on higher altitudes within the ass. Seslerio-Fagetum (V. Planik, M. Planik). In general, this association occurs on the highest altitudes, largest terrain slopes and on the coldest habitats with high EIV values for humidity. Stands of the association on investigated area are very poor in their floristic composition (on average 18,2 species per relevé) in comparison to other areas where this association occurs. This can be explained by the fact that Učka is a mountain which rises directly from the sea and is subjected to influence of Mediterranean climate from almost all directions. Besides, mountain massif above 1100 m is very small and simply there is not enough space which could by its size support harsh climate conditions and longer snow maintenance and therefore creating by these means favourable conditions for growth of higher number of high-mountain species (Šugar 1970).
KEY WORDS: Učka Nature park, beach forests, floristic composition, ecological factors, Istria, Croatia