Remnants of naturalness in a reclaimed land of central Italy

Wetlands are among the most fragile habitats on Earth and have often undergone major environmental changes. As a study case in this context, the present work aims at increasing the floristic knowledge of a reclaimed land now turned into an agricultural lowland with scarce patches of natural habitats. The study area is named Piana di Rosia, and it is located in southern Tuscany (Italy). The compiled checklist consists of 451 specific and subspecific taxa of vascular plants. The life-form spectrum shows a predominance of hemicryptophytes, followed by therophytes. The chorological spectrum highlights a co-dominance of Euri-Mediterranean and Eurasian species along with many widely distributed species. The checklist includes seven species of conservation concern, three Italian endemics (Crocus etruscus Parl., Polygala vulgaris L. subsp. valdarnensis (Fiori) Arrigoni, and Scabiosa uniseta Savi), 41 alien species, 21 segetal species, and 11 aquatic macrophytes of which five helophytes and six hydrophytes. This study suggests that irreversible land-use changes in wetlands can lead towards a simplification of the flora. However, despite the deep transformations that the former wetland has undergone, the presence of some aquatic and protected taxa is interesting. From a conservation point of view, the natural value of this agricultural area could be enhanced and its current management partly reconsidered, thus preserving the remnants of naturalness present.


Introduction
Wetlands are acknowledged to be among the most biologically productive ecosystems (Ramsar Convention on Wetlands 2018). They play a major role in the water cycle by receiving, storing and releasing water, regulating flows, and supporting life. River channels, floodplains and connected wetlands play a significant role in hydrology. Wetlands work as natural sponges that trap and slowly release surface water, rain, snowmelt, groundwater, and floodwaters. Besides, their holding capacity helps to control floods and prevents water logging of crops (Environmental Protection Agency 2020). Moreover, wetlands contribute to the regulation of microclimate, while wetland vegetation slows the speed of floodwaters and helps in distributing them over the floodplain.
In the Mediterranean Basin, natural wetland habitats decreased in extension by 10% between 1975(Mediterranean Wetlands Observatory 2014. This loss is mainly due to land conversion to agricultural land-use and urbanization (Gardner et al. 2015). Land-use changes and the implementation of artificial water systems have reduced the connectivity in many river systems and floodplain wetlands (Ramsar Convention on Wetlands 2018). The environmental changes that wetlands underwent during the last century significantly depleted their unique biodiversity. Furthermore, human activities often simplified geomorphology, eliminating important environments such as transitional ones that connect wetlands and dryer areas, whose flora and fauna are among the most threatened (Alessandrini 2000).
In Europe, the loss of wetland biodiversity is a consequence of the declining extent and quality of wetland habitats (Janssen et al. 2016). However, in Italy, freshwaters host many threatened species and habitats (Gigante et al. 2016(Gigante et al. , 2018Orsenigo et al. 2020). Consistently with the general trends at larger scales, also many wetlands of southern Tuscany have suffered a decrease in extent. Such reduction has generally caused an overall decline in plant diversity, with the disappearance of native species and an increase of non-native ones Lazzaro et al. 2020;Viciani et al. 2020).
This study concerns a lowland known as Piana di Rosia, located a few kilometers southwest of Siena (Tuscany, central Italy). This former wetland turned into an intensive agricultural area in the 19 th century. Though, land-use change and human impact led to a substantial loss of the humid habitats, relict elements of naturalness, related to more or less humid environments, are present.
In Tuscany, information at the species level is usually easily available as it is embedded in floristic online databases (i.e., Wikiplantbase #Toscana -Peruzzi and Bedini 2015 onwards; Peruzzi et al. 2017a), where data arising from studies on a different scale (Arrigoni 2016(Arrigoni -2018Bonari et al. 2016Bonari et al. -2019Cannucci et al. 2019), as well as herbarium specimens and field observations, are stored. This data availability has also facilitated the study of the patterns of Tuscan floristic richness (D'Antraccoli et al. 2019). However, unlike many well-studied neighbouring areas (Mariotti et al. 1986;Chiarucci et al. 1993;Landi et al. 2002Landi et al. , 2009Landi et al. , 2016, floristic knowledge of the Piana di Rosia is very scarce (Angiolini et al. 2005), except for some recent floristic findings (Peruzzi et al. 2017b(Peruzzi et al. , 2017c(Peruzzi et al. , 2018. Also, only a few herbarium samples and a few literature sources can testify for the diversity of aquatic plants once present (Caruel 1860; Baroni 1908). Therefore, we aim at increasing the floristic knowledge of southern Tuscany in the context of a transformed landscape by providing an inventory of the vascular plants of the Piana di Rosia.

Study area
The Piana di Rosia is a lowland plain of central Italy that covers 23.23 km 2 and is located about 10 km southwest of Siena (southern Tuscany, 43°14'38"N, 11°15'35"E). The average elevation is 190 m a.s.l., ranging between 180 and 250 m a.s.l. The area lies within the municipality of Sovicille, in the administrative province of Siena, and is surrounded by small villages (Fig. 1).
The study area borders the Special Area of Conservation (SAC) "Montagnola Senese" (IT5190003) along its western side, and the SAC "Alta Val di Merse" (IT519006) along its southwestern side. The Nature Reserve "Alto Merse" is also nearby present (in Suppl. material 1: Fig. S1).
The study area is dominated by alluvial and lake deposits. The alluvial deposits occur in the central and southern part and have a mainly gravelly and/or sandy texture. Lake sediments occur along the borders of the study area, at slightly higher elevations. In the eastern part, eluvian-colluvial deposits occur. In the northeastern part, where superficial deposits are missing, marine Pliocene deposits emerge (mudstones and sandstones). An outcrop of Miocene continental breccia (limestone) is present near the village of Malignano (Martini 2011;Martini 2012, 2013). The study area is part of a wide aquifer (Luco aquifer), which extends northwards between the Montagnola Senese area, Pian del Lago area, and the village of Monteriggioni. The aquifer mainly develops within the Breccia di Grotti Formation (Barazzuoli et al. 2020).
The bioclimate of the study area can be classified as Oceanic sub-Mediterranean (Temperate sub-Mediterranean macrobioclimate). The thermotype is lower mesotemperate and the ombrotype is upper sub-humid. Regarding the continentality, the climate is weakly semi-continental (Pesaresi et al. 2014(Pesaresi et al. , 2017. The position of the plain surrounded by hills enhances temperature excursions, both daily and seasonal. According to the nearby weather station of San Rocco a Pilli, in the period 2008-2018 the mean annual temperature was 14.3 °C. January was the coldest month (mean temperature 5.3 °C) and July the hottest month (24.2 °C). Freezing temperatures are common in winter, due to thermal inversion. The recorded temperature extremes are about -10 °C and 40 °C. According to the nearby weather station of Rosia, in the period 1951-1997 the mean annual rainfall was 962 mm. Summer was the driest season (125 mm) and winter the wettest one (252 mm).

Landscape transformation
The Piana di Rosia was formerly an ancient wetland reclaimed in the 19 th century for agricultural purposes. The plain was neither included in the existing inventory of the marshy areas of Tuscany (Arrigoni 1981), nor in the review on the status of geobotanical knowledge of the Tuscan wetlands (Tomei 1982). This testifies that the landscape has been heavily modified and cannot be considered a wetland anymore. The wetland extended along the middle course of the Merse River and some of its tributaries (Favilli et al. 2017). Like elsewhere in Italy, in the 1950s traditional agro-pastoral practices began to be gradually replaced by intensive agriculture. This led to the disappearance of the traditional agricultural landscape, highly diversified and hosting frequent patches of natural and semi-natural vegetation, with a shift towards a simplified agro-ecosystem represented by large arable fields and artificial water channels (Suppl. material 1: Fig. S2). Unlike other lowlands of the Siena territory, Piana di Rosia was cultivated already in the first half of the nineteenth century (Greppi 2014). In the last decades, this territory is experiencing a phase of 'attrition', a stage in the process of fragmentation when only very small and isolated patches of natural vegetation remain (Hunter and Gibbs 2007). Elements such as riparian woods, swampy areas, shrublands, and grasslands, are present (Fig. 2).

Current land-use types
The main land-use types in the study area derive from thematic maps of Regione Toscana (2020) (Suppl. material 1: Fig. S3). About 90% of the study area is devoted to agricultural land use. Arable crops are the main ones, including winter cereals (mainly Triticum sp. pl.), corn (Zea mays L.), sunflower (Helianthus annuus L.), and sorghum (Sorghum bicolor (L.) Moench). Woody crops are much less common and include olive groves (Olea europaea L.), walnut groves (Juglans regia L.) and vineyards (Vitis vinifera L.). The rest is occupied by urban and industrial areas (6.0%), broad-leaved forests (1.6%), an airport (1.0%), transitional forest-shrub formations (0.9%), and inland waters (0.04%). The latter include small lakes and main streams, but not artificial channels, which are mapped as deciduous or transitional shrubs.

Field surveys and data analysis
We carried out floristic surveys from 2017 to 2019 in all the land-use types, but excluding urban and industrial areas, with the exception of the airport area, that are limited in extension and out of our aim. The investigations were performed in all seasons. The collected specimens are stored in the herbarium SIENA (acronym follows Thiers 2020 onwards). Species were mainly identified according to Pignatti (1982), Pignatti et al. (2017-2019), and occasionally by using Fiori (1923)(1924)(1925)(1926)(1927)(1928)(1929). We used other floras or specific publications for critical groups including Tutin et al. (1964Tutin et al. ( -1980, Castroviejo et al. (1984Castroviejo et al. ( -2005, Rameau et al. (1989Rameau et al. ( , 2008, Tison and De Foucault (2014), Arrigoni (2014Arrigoni ( -2018, Di Natale et al. (2020). Taxonomic nomenclature follows the updated Italian checklists of the native ) and alien ) vascular flora and subsequent updates summarised in the Portal to the Flora of Italy (2020 onwards; see also Martellos et al. 2020). The order of families follows  and , whereas species are arranged in alphabetical order.
To highlight chorological novelties, we checked species distribution at the administrative province, region and national levels (Peruzzi and Bedini 2015 onwards; Portal to the Flora of Italy 2020). To verify the conservation concern of each taxon, we checked the Tuscan attention list, the Italian and European Red Lists of vascular plants, the list of rare or threatened European arable plants, and the IUCN Red List of threatened species (Sposimo and Castelli 2005;Bilz et al. 2011;Castelli 2012;Rossi et al. 2013;Storkey et al. 2012;Orsenigo et al. 2020;IUCN 2021). We detected Italian endemic taxa according to Bartolucci et al. (2018a, b, c). Alien species, their introduction time in Italy, and naturalization status categories in the study area follow Galasso et al. (2018a, b, c). With regard to the alien status, we distinguished three categories, i.e., casual (unable to form self-maintaining populations), naturalized (occurring with self-maintaining populations), and invasive (occurring with self-maintaining populations and being able to spread over a large area) . Concerning the introduction time, we distinguished between archaeophytes, introduced before 1492, and neophytes, introduced after 1492 ( ). Since Piana di Rosia is an agricultural area, we checked segetal species, i.e., typical "weeds" of wheat and similar crops, following Fanfarillo et al. (2020a). Within segetal species, we checked the presence of strictly segetal species, i.e., those species strictly dependent on such crops. Life forms and chorotypes follow Pignatti (1982), with the exception of alien species (Galasso et al. 2018a, b, c).
Finally, we calculated a Species-Area Relationship (SAR) strictly based on the extension of the study area according to the formula proposed by D' Antraccoli et al. (2019). This formula provides constants for Tuscany that allow to calculate the expected species in an area. We calculated the expected number of species for all taxa, native taxa and alien taxa.
Graphs were drawn using R Studio v. 3.6.0 (R Core Team 2020).

Floristic inventory
The floristic checklist includes 451 specific and subspecific taxa for the study area (Suppl. material 1: Floristic inventory). The taxa belong to 283 genera and 75 families. We recorded 442 Angiosperms, eight fern and fern allies, and one gymnosperm (Juniperus communis L.).
Overall, we found seven species of conservation concern. One species ( With regard to Amaranthus hybridus subsp. cruentus (L.) Thell., several historical specimens are present in SIENA, but many of these specimens were collected at the Botanical Garden of Siena with no clear indication as to whether they were cultivated plants or not, whereas others have no locality.
We found 16 rare native taxa that represent the second or third recent record in the administrative province of Siena. We found 21 segetal taxa in the study area. Among the segetal species, four are strictly segetal, i.e., strictly related to wheat fields and similar habitats, and they are Alopecurus myosuroides Huds. subsp. myosuroides, Bunium bulbocastanum L., Delphinium consolida L. subsp. consolida, and Legousia speculum-veneris (L.) Chaix subsp. speculum-veneris, the latter being the only segetal species of conservation concern in Europe. The other species are typical for segetal habitats, but commonly occur also in other open and more or less disturbed habitats: Anisantha diandra (

Discussion
We studied a reclaimed land of central Italy that is currently an agricultural area. Our floristic surveys revealed the presence of a relatively rich vascular flora in the study area, thanks to the diversity of the habitats present, although most of them occur as small patches. In particular, wetlands and relict woods represent the most relevant elements. Therefore, our results suggest that, despite the conversion to agricultural land, former wetlands host particular species, especially in particular remnant habitats.
The abundance of Poaceae, Asteraceae, and Fabaceae is similar but not consistent with the pattern known for the Italian flora, as the abundance of the first two families in the Italian flora is reversed. The families with fewer species largely follow the trend of the Italian flora ).
The high proportion of annual species, mostly linked to non-hygrophilous communities as found by Angiolini et al. (2011), is related to the large surfaces used as agricultural areas, especially as arable land. The repeated tillage and the disturbance of the sites promotes therophytes in arable crop fields (Fanfarillo et al. 2020a). Though forests and shrublands are generally rare in the area, we found a relatively high diversity of phanerophytes and nanophanerophytes. The abundance of geophytes is partly related to residual natural and semi-natural habitats (e.g., Anemonoides nemorosa (L.) Holub, Petasites hybridus (L.) G.Gaertn., B.Mey. & Scherb. subsp. hybridus), but also promoted by tillage practices as reflected by species as Cirsium arvense (L.) Scop., Gladiolus italicus Mill., and Sorghum halepense (L.) Pers.). On the contrary, we recorded only few aquatic species due to the limited surfaces of wetlands, nowadays corresponding to artificial water bodies and channels, which, especially these latter, tend to dry out in summer. However, species related to wet or partially wet environments are present, such as Althaea cannabina L., Lysimachia nummularia L., Lythrum tribracteatum Salzm. ex Spreng., and Sparganium neglectum Beeby. This is in accordance with other Tuscan wetlands under a strong anthropogenic pressure (Lastrucci et al. 2010. Palustrine and lacustrine plants and plant communities might respond differently to different environmental factors . The chorological spectrum is in line with the life-form spectrum, highlighting a transition between the Mediterranean and Temperate climate. Both, European and Mediterranean species are abundant, with a slight predominance of the former. The high number of widely distributed species is largely due to the occurrence of synanthropic plants (e.g., Alopecurus myosuroides Huds. subsp. myosuroides, Chenopodium album L. subsp. album, and Poa annua L.) and only partially to aquatic plants (e.g., Alisma plantago-aquatica L., Glyceria fluitans (L.) R.Br., and Schoenoplectus lacustris (L.) Palla). Alien species (e.g., Artemisia verlotiorum Lamotte, Amaranthus retroflexus L., and Datura stramonium L.) are abundant due to the high anthropogenic influence. By contrast, the Italian endemics are scarce. Among them, Crocus etruscus Parl. is included in several lists of threatened plant species. This species is a geophyte endemic to Tuscany, Umbria, and Emilia-Romagna. It grows in forests and at forest edges or, less frequently, on grasslands, from 200 to 800 m a.s.l. It flowers between February and April. In our study area, the species was found in deciduous woods with Castanea sativa Mill., Quercus cerris L., Q. pubescens Willd. subsp. pubescens, and Q. robur L. subsp. robur. The populations are not subjected to particular threats, except for a pressure exerted by wild ungulates or human foraging (Ercole et al. 2016).
The presence of endemics and species of conservation concern, both nationally and locally, is useful to assess the status and quality of a flora and of the environment. As mentioned, in our study area such species are very few. This is predominantly linked to the high human impact but might also be due to the lack of specific substrates, morphology or any other particular environmental features. For example, the Piana di Rosia lacks areas with outcropping rocks. This deficiency is partially compensated by the presence of dry-stone walls, boulders, dirt roads, and road edges. Here, we found characteristic species of outcrops or habitats with low soil formation, such as Cerastium sp. pl., Cymbalaria muralis G.Gaertn., B.Mey. & Scherb., Sedum sp. pl., and Veronica cymbalaria Bodard. Even though such areas are limited and small in size, they host numerous species.
The alien species we found are mostly neophytes and their amount is considerable, with every tenth species being an alien one. The local naturalization status of such taxa mostly matches their status on a regional level, except for a few species that are considered casual or naturalized in the study area, but that are naturalized or invasive in Tuscany, respectively, such as Abutilon theophrasti Medik., Fagopyrum esculentum Moench, Helianthus tuberosus L., Mirabilis jalapa L., and Oxalis articulata Savigny. Despite the relatively high presence of alien species in the Piana di Rosia, not many species behave as invasive when compared with the whole Italian flora . The most invasive herbaceous species are Amaranthus sp. pl., Erigeron sp. pl., and Paspalum distichum L., while the most invasive woody aliens are Ailanthus altissima (Mill.) Swingle, Parthenocissus quinquefolia (L.) Planch., and Robinia pseudoacacia L. Some of them, namely A. altissima, Amaranthus sp. pl., Erigeron sp. pl., and R. pseudoacacia, are very frequent and well-established aliens in Italy, and very common in different plant communities . Moreover, R. pseudoacacia and A. altissima have a heavy impact on natural habitats in the study area, mirroring what is reported at the national scale (Radtke et al. 2013;Lazzaro et al. 2020).
In the study area, we found new alien species for the administrative province of Siena. Among the most invasive ones, there are Amaranthus hybridus subsp. cruentus (L.) Thell. and A. powellii S.Watson. This is consistent with the invasive character of many species of the genus Amaranthus and with their relevance as agricultural weeds (Iamonico 2015). We also found scarcely observed aliens for the administrative province of Siena, such as Abutilon theophrasti Medik., Datura stramonium L., and Erigeron annuus (L.) Desf., and interesting floristic records such as Populus canescens (Aiton) Sm. This species grows in riparian woods and humid environments (Pignatti et al. 2017(Pignatti et al. -2019. The discovery of this new phanerophyte for the province of Siena is relevant in the context of the woody flora of Tuscany (Roma-Marzio et al. 2016). The rediscovery of Allium longispathum Redouté, Bromus commutatus Schrad. subsp. commutatus, and Persicaria maculosa Gray confirms the importance of complete floristic surveys, since these taxa are likely commonly distributed, but scarcely observed. The record of Lythrum tribracteatum Salzm. ex Spreng. is the third record for the province of Siena. Its occurrence was previously known at Chiusi and Montepulciano Lakes (Arrigoni and Ricceri 1981). Similarly, Conium maculatum L. subsp. maculatum was reported in recent times at only a few sites in the south of the Siena province (Selvi 1996). We found other relatively rare species such as Isatis tinctoria L. subsp. tinctoria, rare in Tuscany (Peruzzi et al. 2017c). Some species new to the province of Siena, such as Fragaria viridis Weston subsp. viridis and Spergularia rubra (L.) J.Presl & C.Presl, are common in Tuscany, but not in the province of Siena, where they are, however, likely to be scarcely observed.
The analysis of segetal species revealed that most of the taxa are not of conservation concern in Europe, since all are common and widespread. This is consistent with the fact that agriculture in the area is mostly intensive, and thus there is a lack of the typical species-rich fields common in many traditional agricultural areas of Italy (Fanfarillo et al. 2019b;Fanfarillo et al. 2020b). Practices such as chemical weeding and fertilization, that feature the intensively managed arable fields of Piana di Rosia, cause a reduction of segetal biodiversity (Richner et al. 2015;Fanfarillo et al. 2019a). The only exception is represented by Legousia speculum-veneris (L.) Chaix subsp. speculum-veneris, which is considered of conservation concern at the European level. This species is in fast regression under the pressure of intensive agriculture, like other segetal species (Storkey et al. 2012;Richner et al. 2015). However, L. speculum-veneris (L.) Chaix subsp. speculumveneris is relatively common in the Italian peninsula.

Conclusions and implications for conservation
This work contributes to the knowledge of the vascular flora of a poorly studied area of southern Tuscany, a former wetland of the previous century. Our results suggest that the land-use changes that occurred in the Piana di Rosia have modified the typical wetland flora and caused a general simplification of the plant species present. Further, the overall number of species and the number of native species present is lower than expected, while the opposite is true for alien species. Despite this, remnants of natural or semi-natural vegetation, like residual woods and shrubs, together with the presence of natural and artificial small water bodies, allow the presence of interesting plant species occurring in relatively undisturbed habitats, such as endemics, relatively rare species, protected species, and hydrophytes. We also found some species that have not been reported in the administrative province of Siena for over a century. These features are typical of "type 2" of the High Nature Value farmlands, i.e., "farmlands with a mosaic of low intensity agriculture and natural and structural elements, such as field margins, hedgerows, stone walls, patches of woodland or scrub, small rivers etc." (Keenleyside et al. 2014). However, the Piana di Rosia is currently not qualifiable as a High Nature Value farmland due to the intensive land use. In this context, the most biologically valuable areas are ecological corridors bordering channels, streams, ditches, residual groves, highlighting the problem of the reduced surface of these elements and a generalized habitat fragmentation. Residual wetlands within agroecosystems should be maintained, as they offer fundamental niches for numerous hygrophilous species, suggesting that many relevant species might be commonly overlooked, also in areas with a currently scarce natural importance.
Although this study fills a gap in the floristic knowledge of southern Tuscany, our data also suggest that the knowledge of southern Tuscany is far from complete and further botanical and ecological investigations are generally needed, also in areas with an alleged scarce environmental value. Accordingly, surveying and inventorying plant biodiversity in current agroecosystems is fundamental for what they have represented in the past, but also for a better application of sustainable management in the future, in the perspective of preserving valuable elements and restore ecosystem functioning and services (Zerbe 2019). Our findings suggest that an ecological intensification of the agroecosystem would be feasible in the area thanks to the remnants of naturalness present. Also, native plant material could be used to increase the extent and quality of natural and semi-natural elements in the agricultural mosaic. This would help to make such remnants more valuable, also considering that restoration of these agroecosystems becomes much more difficult once they have disappeared (Strohbach et al. 2015). From a conservation point of view, the natural value of this agricultural area could be enhanced, and its current management partly reconsidered, in order to maintain the remnants of floristic naturalness present, bearing also in mind that almost half of the Piana di Rosia borders on protected areas. Lastly, we recall that floristic surveys should become a basic tool for policymakers to calibrate their environment-related decisions.