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ŠUMARSKI LIST 1-2/2017 str. 42     <-- 42 -->        PDF

(FOREST EUROPE, 2015). They are especially endangered and almost disappeared (Leibundgut, 1993; Ellenberg 1996; Parviainen 2005; Matić et al., 2008). Due to outstanding economic value of oak forests, passive, no-intervention conservation faces huge difficulties. They are poorly represented in strict forest reserves networks (Diaci, 1999; Parvainen et al., 2000). Consequently there are rather few opportunities to study their natural dynamics, which makes the adaptation of close-to-nature forestry methods more difficult.
Hüttl et al. (2000) highlighted a lack of knowledge about dynamics of old-growth (semi)-natural forests. Unmanaged forests, regarded as best possible substitutes for natural forests, are popular objects of research (Brang, 2005). Strict forest reserves often have outstanding conservational value (Wesolowski, 2005) as they are biodiversity hotspots, important nature protection sites, considered consequently as conservation baselines (Schmidt, 2005) and as sources of reference data for close-to-nature silviculture (Parviainen et al., 2000). Such old-growth floodplain oak forests are e.g. the March-Thaya (Morava-Dyje) region in the Austrian-Bohemian-Slovak border (Hager et al. 2007 in Hobza 2007; Miklin and Cizek 2014); Prasnik, Stupnički Lug-Cret, Motovunska šuma, Loze and Radiševo, as „special forest reserves” in Croatia (Leibundgut, 1993, Matić 1999, Vukelic et al. 1999). More old-growth pedunculate oak stands („natural forests”) are reported from Transcarpathian Ukraine (Drescher et al., 2003, and Roumania (Borlea, 1999 in Diaci, 1999). Network of strict forest reserves – by definiton: unmanaged forests -- in Germany consists of more than 700 reserves of 31 000 ha; of this Ulmus-Alnus floodplain forest reserves cover only cca. 1000 ha; moist and mesophilous Quercus-Carpinus forests (not necessarily floodplain) cca. 1500 ha (Meyer et al., 2007).
Presumably the best-studied near-natural floodplain hardwood forests in Europe are situated in the March-Thaya (Morava-Dyje) wetland region, at the tristate border of Austria, Czech and Slovak republic, a set of unique forest ecosystems in Central Europe. Parts of it was declared as a Ramsar Site (Hager et al., 2007 in Hobza, 2007) and UNESCO Biosphere Reserve; it includes Ranspurk and Cahnov-Soutok strict forest reserves, woodland pastures and also other sites of Community Importance and Special Protection Areas (Miklin and Cizek, 2014). Its area is cca 200 km2, a cca 65 km long corridor along the rivers, down to the March-Danube confluence. Forests are mainly azonal floodplain forests within zonal Subpannonian mixed oak ones. The two largest continuous forest complexes are cca 1000 ha each. Main species are Quercus robur and Fraxinus angustifolia.
The Austrian part of the March-Thaya region has been studied since the 1970’s. Wendelberger (1973) and Drescher (1985) published phytosociological studies on hardwood forests consisting of Quercus robur, Fraxinus angustifolia and Ulmus laevis, discussing also abiotic factors (flood dynamics, soil characteristics), zonation and successional conditions which are very similar to our sites, as pointed out by Hager et al. (2007). Most of the oak stands are under high forest management with artificial regeneration, although coppice-with standards method is also used based on natural regeneration. On the contrary, Cahnov-Soutok National Natural Reserve, situated at the convergence of Dyje and Morava in the Czeh Republic, is left unmanaged since the 1930s. Whole-area measurement of stand structure had been executed in 1973 (Prusa, 1985). It was repeated in 1994 (Vrska, 1997), and 2006 (Janik et al., 2008; Král et al., 2014). Representation of Quercus robur decreased according to all monitored indicators (number of trees, basal area and volume); at the same time Acer campestre, Tilia cordata and Carpinus betulus increased. An expansion of Crataegus spp. among trees was also noted. A recent publication (Miklin and Cizek, 2014) reports on the perilous disappearance of old-growth forest stands, especially of open woodlands, contrary to conservational accreditations. According to this authors, closed canopy hinders oak regeneration, as closed forests were never naturally dominant in this region.
According to Leinbundgut’s description, the Prašnik „virgin forest” (Croatia, near the Sava river) has 40 m heigh upper canopy layer, dominated by Quercus robur (20-50 individuals/ha – at least partly forest-pasture). Many other species (Fraxinus angustifolia, Ulmus minor, Alnus glutinosa, Carpinus betulus, Acer campestre, Pyrus pyraster, Tilia cordata, T. tomentosa, Fagus sylvatica) occurs sporadically. In the middle and lower canopy layers there are less individuals (20-30/ha), because of the strong shading of wide-crowned oaks in the upper layer. In gaps formed by the death of old trees, dense, species rich (Crataegus monogyna and C. laevigata, Viburnum opulus, Prunus spinosa) shrub layer developed, but apparently it did not hinder oak regeneration (Leibundgut, 1993).
Dister (1985) presents an old-growth oak-ash forest from the upper Rhine, near Darmstadt. Its upper layer is 25-30 m high; consists mostly of Quercus robur of 150-190 years, low branching points to former coppice-with-standard management; and of some huge Fraxinus excelsior trees. In the lower levels Fraxinus dominates, due to its better regeneration and less sensitivity to game damage. Oaks are almost totally missing from the lower layers, but can be observed growing up in more enlight ened edges, protected by Crataegus.
Drescher et al. (2003) publishes three relevés from „ancient” oak forests (160-170 years, but coppice-with-standards, except the Atak site) from the Upper Tisza floodplain (Northeastern Pannonian Plain, Transcarpathian Ukraine). Oak regeneration is not discussed explicitly, but Quercus robur is documented in the herb and shrub layer and also from second canopy. Our own unpublished data also prove natural regeneration of Q. robur in this geographic area.
Quercus robur is dominant native species of alluvial hardwood forests, but in closed stands it has a rather poor