White willow (Salix alba L.) woods are the most common wood extensions along the water courses in the plains of Northern Italy; they are mostly included in Habitat 91E0 or in Habitat 92A0, in areas with Mediterranean influence. At present Salix alba woods show a bad state of preservation because of the die-back of the trees of the dominant species which causes a regression of the community that can be schematized in the following phases: (1) death of terminal branches and thinning out of the canopies, (2) tree death and subsequent fall with creation of gaps, (3) persistence of herbaceous or shrubby coenoses with only a few spaced willow trees. The same happens to riparian willow curtains which become more and more fragmented. It is not possible to identify a single cause of this regressive dynamics and we assume that several possible factors are involved in this process: (1) lowering of the water table level in summer due to the deepening of the riverbed, to the withdrawal of water to be used for agriculture and to critical metereological conditions in recent years, (2) to natural senescence of existing wood communities, (3) to phytotoxic effects. The reduction of willow tree cover produces wide open areas in which alien invasive species establish and successfully grow. Moreover no willow renewal takes place due to the peculiar way in which Salix alba wood establish and to the lack of the suitable sites built by natural river geomorphological processes. The management aimed to the preservation of this Habitat must guarantee the conservation of natural geomorphological mechanisms which make spontaneous renewal possible and must avoid an excessive lowering of river water in summer due to agricultural uses.

Elementi di criticità nella conservazione dei saliceti a Salix alba in Pianura Padana.

BRACCO, FRANCESCO;ASSINI, SILVIA PAOLA
2013-01-01

Abstract

White willow (Salix alba L.) woods are the most common wood extensions along the water courses in the plains of Northern Italy; they are mostly included in Habitat 91E0 or in Habitat 92A0, in areas with Mediterranean influence. At present Salix alba woods show a bad state of preservation because of the die-back of the trees of the dominant species which causes a regression of the community that can be schematized in the following phases: (1) death of terminal branches and thinning out of the canopies, (2) tree death and subsequent fall with creation of gaps, (3) persistence of herbaceous or shrubby coenoses with only a few spaced willow trees. The same happens to riparian willow curtains which become more and more fragmented. It is not possible to identify a single cause of this regressive dynamics and we assume that several possible factors are involved in this process: (1) lowering of the water table level in summer due to the deepening of the riverbed, to the withdrawal of water to be used for agriculture and to critical metereological conditions in recent years, (2) to natural senescence of existing wood communities, (3) to phytotoxic effects. The reduction of willow tree cover produces wide open areas in which alien invasive species establish and successfully grow. Moreover no willow renewal takes place due to the peculiar way in which Salix alba wood establish and to the lack of the suitable sites built by natural river geomorphological processes. The management aimed to the preservation of this Habitat must guarantee the conservation of natural geomorphological mechanisms which make spontaneous renewal possible and must avoid an excessive lowering of river water in summer due to agricultural uses.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11571/823552
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