Oecesis of White Willow Communities in the Nature Reserve Vestonicka nadrz reservoir

Abstract

Maděra P., Svobodova I., Packova P.: Oecesis of white willow communities in the Nature Reserve Věstonicka nadrž reservoir. Ekologia (Bratislava), Vol. 28, No. 1, p. 7–21, 2009. The construction of Nove Mlýny water reservoir has caused the break of floodplain corridors connectivity between alluviums of Dyje, Svratka and Morava rivers. The Czech Ministry of Environment adopted the ecologisation policy of Nove Mlýny middle water reservoir after 1989. Within this policy the water level was lowered by 85 cm in July of the 1996 (to the spot height 169.5 m a. s.l.). Two artificial islands were built up to perform as a part of regional biological corridor running through middle water reservoir. After the lowering of water surface level in the reservoir 80 ha of banks arised and in the Jihlava and Svratka rivers confluence in process of intensive sedimentation formed a new island. The viable seeds of anemochorous willow and poplar trees could not show up in the air in July, at the time of water surface level lowering, because a rain of seeds is present only in May and June. Nevertheless in September the depositions without vegetation were covered by the white willow and black poplar seedlings. The population density reached as many as 45 specimens per square meter. The paper describes the way of white willow communities oecesis in nature reserve Věstonicka nadrž reservoir. The phenology of Salix alba, seeds rain and seeds germination in dry environment and in water were observed. The seeds of Salix alba had the germinative activity in dry environment most 17 days (2,5% of seeds). In water seeds germinated promptly and seedlings lived on more than 40 days. The oecesis was made thanks to „a seedlings waterbank“. The seedlings were washed up on the uncovered depositions and lakesides. The white willow behaves in juvenile phase in water as a natant or submerged hygrophyte species and prolongs its ability to occupy a new territory.