River Re-naturalisation in the Tisza River Basin after Forest Cutting Activities

Forest cutting is a typical kind of economic activity in the Ukrainian Carpathians. Forest cutting within a river basin and especially timber transportation downstream the rivers leads to almost complete de- struction of the river habitats. River re-naturalisation actions, taken by the authors included clearing of timber remains, restoration of natural conditions by means of building rapids, spits and capes from local stones, and creation of depth drops and areas with different flow velocity and turbulence in the Skorodniy stream. These works were followed by stocking the stream with invertebrates and fish. The hydrobionts for stocking were collected in an undisturbed river, similar to the Skorodniy stream by its size, underly- ing rock and altitude. Mechanical destruction of habitats and excessive amount of timber residues lead to the condition when rivers, influenced by intensive forest exploitation, face replacement of litorheophilic fauna by xylophytous and perophilic species. After wide development of xylophytous shredders (Amphipoda), some eurybiontic predators (Hirudinea) appear, then come gatherers (larvae of Chironomidae), etc. Under conditions where the whole riverbed suffers, such "defective" communities can exist for years. In such cases, the general abundance rates, biodiversity and the functional activity of bottom fauna remain rather low, while even little efforts for re-naturalisation may lead to fast restoration of the river biota.