Narrow-leaved ash (Fraxinus angustifolia V a h l) in the structure of floodplain forests of Croatian Posavina

The research was conducted in the area of Croatian Posavina, in the floodpl ain belt of the river Sava. The structural features, and economic and non-m arket values of narrow-leaved ash stands in relation to site conditions wer e analysed. In terms of principal tree species. the sites in Posavina can b e divided into oak and ash sites. The differentiation between these, and especially the transitional ones, is of primary importance for forestry, as management goals and methods, parti cularly the method of regeneration, depend on the properties of the sites. Narrow-leaved ash grows in three groups of sites called wet micro-depressio ns, unsoaked micro-depressions and micro-elevations, with characteristic so ils consisting of amphigleys, hypogleys and semigleys. The local names of t hese sites (bara, niza and greda), in fact reflect the water regime and the micro-relief with minimal relative height differences of occasionally only 10 cm. Narrow-leaved ash grows successfully in all the above-mentioned sit es, but forms pure ash stands only in wet micro-depressions. The changing micro-relief in micro-depressions cause stands to have differe nt properties. So, there are wet, humid and dry types of pure narrow-leaved ash stands in a micro-depression. In an unsoaked micro-depression, narrow- leaved ash grows in mixed stands with pedunculate oak. On a micro-elevation , it is mixed with pedunculate oak and common hornbeam. The least favourabl e site conditions for the growth of forest trees are found in wet micro-dep ressions, slightly better ones are in unsoaked micro-depressions, while the most favourable ones exist on micro-elevations, Due to its ecological char acteristics and biological properties, narrow-leaved ash is capable of tole rating various sites. As highly unfavourable swampy conditions can be toler ated only by narrow-leaved ash, this is the reason why wet micro-depression s are inhabited by pure ash stands. In other sites, more favourable conditi ons allow the growth of other tree species, in particular of pedunculate oa k, which results in the establishment of mixed stands. Stands of narrow-lea ved ash growing in wet micro-depressions have very low economic value compa red to other stands in which it occurs. However, their ecological and socia l value is high.