Paesaggi vegetali, biodiversità cenotica e funzionalità fluviale. Il caso del fiume Tagliamento.

2011/2012Analisi delle unità di paesaggio fitocenotico lungo il fiume Tagliamento.XXIV Ciclo197

Conservation of plant diversity of karst dry grasslands by the reintroduction of grazing. The case study of Basovizza/Bazovica in the Italian Karst

Floristic and vegetation studies were conducted in an experimental area of the Italian Karst at Basovizza/Bazovica included in the Natura 2000 site \u201cCarso Triestino e Goriziano\u201d to assess the effects of the reintroduction of grazing on plant species and communities. In the area, partially deforested in 2006, cattle, sheep and goats were introduced in the summer of 2007. A monitoring programme for plant populations was performed focusing on four target species typical of the karst dry grasslands: Rock Knapweed Centaurea rupestris, Green-winged Orchid Orchis morio, Toothed Orchid Orchis tridentata and Mountain Pasqueflower Pulsatilla montana. Three exotic invasive species, detrimental to grazing, were also included: Tree of Heaven Ailanthus altissima, Narrow-leaved Ragwort Senecio inaequidens and Common Ragweed Ambrosia artemisiifolia. For each species, the GPS position was taken both for individuals and large groups of plants; a count of the individuals present at each measured point was performed too. In order to verify the process of re-colonization by species of calcareous dry grasslands, phytosociological relev\ue9s were carried out in areas previously occupied by Black Pine (Pinus nigra) plantations, woods with Downy Oak (Quercus pubescens) and Hop Hornbeam (Ostrya carpinifolia) and thermophilous scrub of Common Juniper (Juniperus communis), documented from vegetation maps made in 2005. For each vegetation type 6 permanent plots were selected, in which phytosociological relev\ue9s were carried out to. The study shows that in the areas of the original karst dry grassland more widely distributed species typical of the habitat remain. In overgrazed areas the grassy turf is discontinuous, segetal terophytic species of the class Stellarietea mediae entering into the gaps. Cover of the Musk Thistle (Carduus nutans) has increased significantly, as spiny species are not palatable to animals. The occasional presence of neophytes such as Daisy Fleabane (Erigeron annuus) and Canadian Horseweed (Conyza canadensis) was also found. In undergrazed areas, however, the natural processes of succession and scrubbing over are taking place. In the areas formerly occupied by pine plantations and woods with Quercus pubescens and Ostrya carpinifolia, Autumn Moor Grass (Sesleria autumnalis) and Rock Tor-grass (Brachypodium rupestre) are still able to become covered by a compact herbaceous sward. An abundant presence of Carduus nutans and the entry of Senecio inaequidens, the latter especially abundant on wood chips derived from tree clearing, were encountered as well as the spread of Ailanthus altissima favoured by the opening up of the scrubland