The Nature 2000 Site ‘Selva Pisana’ (Parco Regionale di Migliarino, San Rossore, Massaciuccoli) includes three habitats distributed in a continuum: riparian forests (91F0 Habitat code), alluvial forests (91E0), and small patches of sub-Atlantic and medio-European forests (9160). Detailed floristic and vegetation inventories are available for this site from the second part of the last century (1,2,3). According to them, riparian forests can be attributed to the association Fraxino-Quercetum roboris Gellini, Pedrotti and Venanzoni 1986, with the subass. carpinetosum betuli, and alluvial forests to the association Carici-Fraxinetum angustifoliae Pedrotti, 1970, with the subass. alnetosum Gellini, Pedrotti and Venanzoni 1986. Around year 2000, the former association was still the most diffused broadleaved vegetation in the area, while the latter was restricted to very humid soils, often flooded also in spring and summer (2,3). In the last two decades, treefall increased dramatically, with Quercus robur being the most affected species. Trees underwent both trunk crash and uprooting, which was generally ascribed to extreme summer drought (Fig. 1). To confirm this hypothesis, historical data were compared with floristic inventories carried out in the corresponding forest stands from 2023 to 2025. The Ecological Indicator Values of Ellenberg (EIV) were attributed to species according to the adaptation to the Italian flora made by Pignatti and were weighted according with the ordinal method transforming the Braun-Blanquet cover values in figures from 1 to 9. The analysis of vegetation in a stand which was once attributed to the association Fraxino-Quercetum roboris with an abundant layer of Ruscus aculeatus (1,3), showed today a marked shift towards species indicating increased soil humidity and higher solar radiation (Fig. 2). The occurrence of hygrophilous species like Limniris pseudacorus and Carex riparia in the understory, so as the rare presence of Quercus robur in the tree layer, indicate a shift of vegetation towards the association Carici-Fraxinetum angustifoliae. These results support the hypothesis that the primary cause of tree dieback is increased soil humidity rather than drought, which was probably caused by the abandonment of drainage-channel management. The expansion of alluvial forests to the expense of more mesophile riparian forests is occurring in several parts of the forest of San Rossore and should deserve special attention. Indeed, riparian forests are High Conservation Value habitats in the Mediterranean region and host extra-zonal species like Quercus robur, Carpinus betulus, Veronica montana, Cardamine apennina, Digitalis micrantha, and Lilium bulbiferum, which cannot ‘move’ to drier soils following natural dynamics, because these soils are occupied by farmland, and industrial and urban settlements.
Ellenberg Indicator Values demonstrate community shift and habitat loss in the forest of San Rossore (Nature 2000 Site ‘Selva Pisana’)
Iduna Arduini
;Matteo Diana;Riccardo Lenci
2025-01-01
Abstract
The Nature 2000 Site ‘Selva Pisana’ (Parco Regionale di Migliarino, San Rossore, Massaciuccoli) includes three habitats distributed in a continuum: riparian forests (91F0 Habitat code), alluvial forests (91E0), and small patches of sub-Atlantic and medio-European forests (9160). Detailed floristic and vegetation inventories are available for this site from the second part of the last century (1,2,3). According to them, riparian forests can be attributed to the association Fraxino-Quercetum roboris Gellini, Pedrotti and Venanzoni 1986, with the subass. carpinetosum betuli, and alluvial forests to the association Carici-Fraxinetum angustifoliae Pedrotti, 1970, with the subass. alnetosum Gellini, Pedrotti and Venanzoni 1986. Around year 2000, the former association was still the most diffused broadleaved vegetation in the area, while the latter was restricted to very humid soils, often flooded also in spring and summer (2,3). In the last two decades, treefall increased dramatically, with Quercus robur being the most affected species. Trees underwent both trunk crash and uprooting, which was generally ascribed to extreme summer drought (Fig. 1). To confirm this hypothesis, historical data were compared with floristic inventories carried out in the corresponding forest stands from 2023 to 2025. The Ecological Indicator Values of Ellenberg (EIV) were attributed to species according to the adaptation to the Italian flora made by Pignatti and were weighted according with the ordinal method transforming the Braun-Blanquet cover values in figures from 1 to 9. The analysis of vegetation in a stand which was once attributed to the association Fraxino-Quercetum roboris with an abundant layer of Ruscus aculeatus (1,3), showed today a marked shift towards species indicating increased soil humidity and higher solar radiation (Fig. 2). The occurrence of hygrophilous species like Limniris pseudacorus and Carex riparia in the understory, so as the rare presence of Quercus robur in the tree layer, indicate a shift of vegetation towards the association Carici-Fraxinetum angustifoliae. These results support the hypothesis that the primary cause of tree dieback is increased soil humidity rather than drought, which was probably caused by the abandonment of drainage-channel management. The expansion of alluvial forests to the expense of more mesophile riparian forests is occurring in several parts of the forest of San Rossore and should deserve special attention. Indeed, riparian forests are High Conservation Value habitats in the Mediterranean region and host extra-zonal species like Quercus robur, Carpinus betulus, Veronica montana, Cardamine apennina, Digitalis micrantha, and Lilium bulbiferum, which cannot ‘move’ to drier soils following natural dynamics, because these soils are occupied by farmland, and industrial and urban settlements.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
