Saproxylic beetles of the Po plain woodlands, Italy

Abstract Forest ecosystems play an important role for the conservation of biodiversity, and for the protection of ecological processes. The Po plain woodlands which once covered the whole Plain, today are reduced in isolated highly threatened remnants by modern intensive agriculture. These close to natural floodplain forests are one of the most scarce and endangered ecosystems in Europe. Saproxylic species represent a major part of biodiversity of woodlands. The saproxylic insects are considered one of the most reliable bio-indicators of high-quality mature woodlands and have a very important role in regard to the protection and monitoring of forest biodiversity due to their highly specific living environments. As a result of the dramatic reduction of mature forests and the decreased availability of deadwood most of the saproxylic communities are greatly diminishing. The study was conducted in the Ticino Valley Regional Park and the aim is to contribute to the expansion of knowledge on the saproxylic beetles of Lombardy. We investigated 6 sampling sites belonging to alluvial and riparian mixed forests. For each forest we selected 12 trees. For beetles’ collection we used two different traps: Eclector Traps and Trunk Window Traps (total of 72 traps and 864 samples collected). We determined 4.387 beetles from 87 saproxylic species belonging to 21 families. Of these species 51 were not included in the previous checklist of the Park. By comparing the two different techniques used for catching saproxylic beetles, we found a significantly high difference in species richness between Window Traps (WT) and Eclector Traps (ET) with a higher number of species captured in the Window Traps. However, the combined use of two different types of traps significantly expanded the spectrum of insects captured Among the species reported as Least Concern in the IUCN Red List, we found interesting species such as the Elateridae Calambus bipustulats, the Eucnemidae Melasis buprestoides and the following species never previously found in the Park: Cerambycidae Xylotrechus rusticus, the Cetoniidae Valgus hemipterus, the Elateridae Lacon punctatus, the Mycetophagidae Mycetophagus piceus, Litargus connexus. Although we didn’t find species listed in the Annexes of the EU Habitat Directive, some of the species found are locally threatened because of their rarity, local distribution, and strong linkage to old forests. Among these species there are the Bothrideridae Bothrideres bipunctatus, the Cerambycidae Prionus coriarius and Xylotrechus rusticus, the Dryophthoridae Dryophthorus corticalis, the Eucnemidae Nematodes filum (with only 1 individual captured in Alnus unmanged forest), the Histeridae Aeletes atomarius and Paromalus flavicornis, the Laemophloeidae Cryptolestes duplicatus, the Latridiidae Enicmus rugosus and Latridius hirtus, the Mycetophagidae Mycetophagus piceus, and the Zopheridae Colydium elongatum and Pycnomerus terebrans.


Introduction
Forest ecosystems play an important role for the conservation of biodiversity and for the maintenance of ecological processes. Italian forests make up 34.7% of the country's territory and are among the lushest in Europe (European Environment Agency 2006). North Italy, in particular the area of the Po Plain Valley, was once entirely covered by alluvial floodplain forests. Today these kinds of forests are reduced to small remnants, are considered one of most at risk ecosystems, and are strongly threatened by intensive agriculture and industrial activity (Minelli et al. 2002). Two examples of these ecosystems are the "Bosco Della Fontana" in Mantova and the "Ticino Valley Regional Park".
Saproxylic species represent roughly 20-30% of the invertebrate fauna of the European broad-leaved forests (Wermelinger et al. 2002, Vallauri et al. 2005 and constitute a huge part of woodland biodiversity. Moreover, saproxylic insects are considered one of the most reliable bio-indicators of high-quality mature woodlands (Speight 1989, Fowles et al. 1999, Brustel 2001, Alexander 2004, Johnsson et al. 2005 and have a very important role in regard to the protection and monitoring of forest biodiversity due to their highly specific living environments (Schlaghamerský 2000). The role of insects in the decomposition of deadwood and in the distribution of woody debris is essential (Schlaghamerský 2003, Harmon et al. 1986, and their conservation is strongly needed in order to preserve overall biodiversity. As a result of the dramatic reduction in mature forests and the decreased availability of deadwood, most saproxylic communities are diminishing greatly. Several species are suffering from fragmented distribution, and in some cases, are disappearing from their former strongholds (Geiser 1998).
The ecology and distribution of many saproxyilic species in Mediterranean countries are poorly studied or completely unknown (Buse et al. 2010). Data on the saproxylic fauna of lowland forests, particularly on floodplains, is very limited (Nieto and Alexander 2010). The aim of this study is to expand our knowledge about the Italian saproxylic beetle populations and, more specifically, to gain more information about the species present in the floodplain forests of the Po Valley along a gradient of deadwood consumption within the Ticino Valley Natural Park.

Study area
The study was conducted in the Ticino Valley Natural Park located in Northwest Italy 30 km south of the city of Milan. The park, which was acknowledged as the MAB Biosphere Reserve "Valle del Ticino" (UNESCO 2005), covers an area of 287 km along the banks of the Ticino River from Lake Maggiore to its confluence with the Po River. This particular geographic position crosses the most urbanized area of the country and represents an important ecological corridor between the Alps and the Apennines by creating a biological connection between continental Europe and the Mediterranean area. The Ticino Valley represents an area of high biodiversity with a large variety of habitats: conifer forests, lowland forests, waterways, wetlands, cultivated fields, heathlands, and meadows (Bogliani and Furlanetto 1995). In particular, the valley forests represent what remains of the ancient lowland deciduous forests that once covered the plains of northern Italy. Woodlands cover 195.46 km or 60% of the whole natural park and mainly consist of the two habitat types listed in Annex I of the EU Habitat Directive 92/43/CEE (Falco et al. 2008): 1) 91E0* -Alluvial forests with Alnus glutinosa and Fraxinus excelsior (Alno-Pandion, Alnion incanae, Salicion albae) and 2) 91F0* -Riparian mixed forests of Quercus robur, Ulmus laevis, and Ulmus minor.
This study covers two Sites of Community Importance (SCI): "Boschi Siro Negri e Moriano" (IT2080014) and "Boschi di Vaccarizza" (IT2080019) located on the southern side of the Park (Fig. 1) The SCI "Boschi Siro Negri e Moriano" extends along the Ticino River from the bridge of the Milano-Genova highway to the city of Pavia and covers an area of 13.52 km . The SCI has an elongated shape and is inserted inside a broad valley groove with a low slope that widens as you move from North to South. The river is included in a dense hydrographic network represented by irrigation ditches that constitute an interesting environmental and wetland habitat with a high natural value (Perracino 2010). The forest vegetation includes both habitat types described above with the most common trees being the pedunculated oak (Quercus robur), three species of poplars (Populus alba, P. nigra, P. tremulus), and the locust tree (Robinia pseudoacacia) and the most common high shrubs being hazel ( Corylus avellana), hawthorn (Crataegus monogyna), and bird cherry (Prunus padus). The most interesting area in the SCI is the Integral Nature Reserve "Bosco Siro Negri" (BN10). The Reserve, established in 1973, is characterized by the presence of unmanaged lowland forests that represent the vegetation which covered a large part of the Po Valley before Roman expansion (Tomaselli and Gentile 1971).
The SCI "Boschi di Vaccarizza" covers an area of 4.65 km between the city of Pavia and the Southern border of the park; it is completely included inside the Ticino Valley Regional Park, but it's located in an area subjected to deep transformations by human activities. The SCI is located downstream of the confluence of the Ticino River into Po River. In this stretch, the floodplain is very large when compared to many other waterways in the area and is occupied, for the most part, by poplar plantations which characterize the cultivation of the area. Only in the Northern part of the SCI and in the ranges in close contact with the river did we find a more complex vegetation structure (Perracino 2010). The study area includes only the northern part of the SCI and sampling was only carried out in one type of habitat: the wet forests belonging to type "*91E0: Alluvional forests" (Falco et al. 2008) which featured a prevalence of alder trees, Alnus glutinosa.

Study design
We investigated 6 sampling sites consisting of both managed and unmanaged forests. We considered unmanaged forests those which had not been influenced by direct human disturbance for at least 20 years (Paillet et al. 2010). We analyzed data from 2 riparian mixed forests (habitat code 91F0*) dominated by Quercus robur (called here in this paper " Quercus forests") and 4 Alluvial forests (habitat code 91E0*). The Alluvial forests included 2 riparian forests of Alnus glutinosa (Corine Biotope code 44.3 and called in this paper " Alnus forests") and 2 arborescent galleries of tall Salix alba, S. fragilis, and Populus nigra (Corine biotope 44.13: called in this paper "Populus forests").
In the SCI "Boschi di Vaccarizza", we investigated two Alnus forests. In this case we also investigated 1 unmanged forest (V1) and 1 managed forest (V2).
For each forest, we selected and georeferenced 12 trees, 6 fallen and 6 standing, belonging to three decay classes of wood according to the criteria described in the manual "BioSoil -Biodiversity Project" (Cindolo and Petriccione 2006): Class 1 -hard and compact wood with intact bark, Class 2 -hardwood or initial disintegration (penetrable up to 1cm) with bark partially absent, and Class 3 -soft wood (penetrable up to 3 cm or more) with bark almost totally absent. We placed traps on two trees for each decaying class.
For collecting beetles, we used two different traps: 1) Eclector Traps (Alinvi et al. 2007) used for the quantitative sampling of insects emerging from logs in a moderately advanced stage of decomposition and 2) Trunk Window Traps (Kaila 1993) used to sample the total assemblage of flying saproxylic beetles (Fig. 2). Trunk Window Traps (Kaila 1993) and Eclector Traps (Alinvi et al. 2007).

Saproxylic beetles of the Po plain woodlands, Italy
All traps were checked every two weeks from April 2010 to September 2010 for a total of 12 collections from each forest and 864 samples collected during the study. Of the 68 families identified, 48 were found to be saproxylic and we considered obligate saproxyilics to be those beetles which depend on dead wood in at least part of their lifecycle (Gibb et al. 2006). Among the 48 saproxilic families, we choose only 21 families on the basis of there being a significant number of saproxylic species in the family and the availability of a specialist to identify the specimens.

Data analysis
In the analysis, we used the pooled sample of 72 traps (36 windows traps and 36 eclector traps). As a measure of species richness (α-diversity) (Whittaker 1972) we used the number of species caught in each plot because the sampling effort was the same at all the sites. The number of species was log-transformed to approach a normal distribution. We compared species richness among the tree habitat types using a one-way ANOVA and between managed and unmanaged forests using a T-test.

Notes:
The larva is polyphagous and develops under bark on branches and trunks of various dead broadleaves, mainly oak, and also rarely in conifers. The adult is found from May to August on wood in broadleaves woodland ranging from lowlands to mountains (Alexander 2002, Hůrka 2005

Notes:
The species is widespread from the plains to the mountains. The larva develops in the cambial layer of large sections of freshly dead broadleaves wood. The adult is usually found on oaks, and rarely occur on flowers. Anderson 2012, Pesarini andSabbadini 1994).

Notes:
The species is thermophilic. It is found on many hardwoods as rosa, oak, lime, ash, grape, cercis, chestnut, willow, hornbeam, evonymus, birch, robinia, and hibiscus trees, but is also more rarely found in conifers such as fir trees (Pesarini and Sabbadini 1994).

Notes:
The species develops in the dead branches and dead logs of various broadleaves, mainly oak, and also in conifers. The larva makes characteristic borings in the bark and sapwood. The adult is crepuscular and attracted to light and sweet secretions (Alexander 2002 Notes: The species develops in the thin dead branches of a variety of broadleaves especially in old hedgerows (Alexander 2002

Notes:
The species is widespread in both the plains and the mountains. The larva develops for three years in dead wood, mainly in stumps and their roots, and reaches up to 70mm in size. The adult appears in the summer in broadleaves and mixed forests, and also rarely in conifers. It flies at dusk and during the night. It is a species with a declining population (Hůrka 2005, Pesarini andSabbadini 1994).  (2013)).

Notes:
The larva lives in the soil and feeds on the mycelia of fairy ring champignons. The adult appears from June to August on various flowers, mainly in meadows (Hůrka 2005

Notes:
The larva develops under the bark of the dry branch wood of roses and hawthorns, as well as, blackthorns and other fruit trees. The adult appears beginning in April on the twigs, leaves, and flowers of orchards and forest edges (Hůrka 2005

Notes:
The species is more widespread in the Mediterranean area than in continental regions. The larva develops only in oaks. The adult appears during spring and summer on the logs of the host plants (Pesarini and Sabbadini 1994). Notes: The species is rare but widespread as are the other species of the genus. The larva develops under the bark of various broadleaves, mainly birch, poplar, willow, and aspen. The adults mostly occur on stacks of dry branches or logs of host plants and fly and run around in sunshine (Hůrka 2005

Notes:
The species is very common. The larva develops in the rotten wood of old broadleaves with humus-rich soil. It pupates in late summer and autumn in a cocoon in which the beetle overwinters. The adult appears from April to October on the flowers of various herbs, shrubs, trees, and also sometimes at oozing sap (Hůrka 2005

Notes:
The species inhabits the old relict forests of broadleaves and conifers throughout Europe. Despite their wide distribution, this species is pretty rare probably because of its hidden lifestyle and difficulty to collect. The larva develops in the hard wood of oaks and also in beeches and is often associated with the ant Lasius brunneus (Alexander 2002, Pešić 2011

Notes:
The species is principally associated with ancient oak forests. The larva develops in the dead timber of various broadleaves mainly in heart-rot, but also under the bark of rotten limbs. It is a predator of other beetle larvae, often Dorcus sp. (Alexander 2002). Notes: This species is typical of wetlands, particularly the riparian forests of the Lombardy plains. The larva develops in the stumps of different species including both broadleaves and conifers (Platia 1994

Notes:
The species is found in the winter under the bark of old oak trees such as lindens, elms, poplars, and mulberry trees. The larva is a predator living in the soft rotten wood of stumps and trunks on the same plant as the adult, especially oaks (Platia 1994, Alexander 2002

Notes:
The species lives in conifers, mainly pine, and in broadleaves like oak, beech, chestnut, willow, poplar, pear, and lime. The larva develops under the bark of standing and fallen dead trees and in stumps and trunks invaded by ants of the genus Camponotus. The adult has crepuscular and nocturnal habits and is often found together with the larvae (Platia 1994 Notes: The species is common and widespread. The larva develops mainly in rotted timber, but also in decaying wood. The adult flies after dark and is attracted to light (Alexander 2002

Notes:
The species occurs relatively often and throughout the year on tree fungi, especially on beeches where the larva also develops (Alexander 2002, Hůrka 2005.

Notes:
The species is mostly found on beech, hornbeam, and elm trees. The larva develops in rather hard dead timber, especially boughs, of a wide variety of broadleaves (Alexander 2002, Hůrka 2005.

Notes:
The species lives in ancient wood pastures, in beech, ash, willow, and alder trees. It is usually found in the burrows of stag beetles Dorcus parallelipipedus in the moist crumbly decaying heartwood; although it has also been recorded with Sinodendron cylindricum and ant species such as Lasius brunneus (Alexander 2002 Notes: The species lives in old parks and ancient woodlands. It is found under the preferably dead bark of trees such as poplar, willow, oak, beech, walnut, chestnut, and maritime pine trees. It sometimes lives associated with ants such as Lasius fuliginosus and Formica cunicularia. The larva is a predator of other insect larvae and is often found in the burrows of Bostrychus sp. and Crypturgus pusillus. The adult appears in the spring and at the end of summer (Alexander 2002, Vienna 1980

Notes:
The species living range is from hills to mountains and in various types of decaying wood from both standing and fallen trees. The larva develops in poplars, beeches, oaks, and rarely in conifers (Vienna 1980

Notes:
The species lives under the bark of old forest deadwood, mainly in oak but also in ash, beech, alder, and pine trees. It usually lives associated with fungi of the genus Lycoperdacea, Polyporacea, and myxomycetes (Alexander 2002, Rücker 2004

Notes:
The larva and adults can be found in the galleries of ambrosia beetles, at oozing tree sap, and in various fungi. The larva develops in the nests of bumblebees and the adult occur on flowers and during winter can be found in mole nests (Hůrka 2005).
In the SCI "Boschi di Vaccarizza", we collected 1.077 individuals belonging to 17 families and 48 species of which 29 species have never been reported in the Park (   Mean number of saproxylic species captured with Trunk Window Traps and Eclector Traps. Table 3. Difference in species richness among the three habitat type and between managed and unmanaged forests.  Mean number of saproxylic species captured in the three habitat type with both Trunk Window Traps (dark gray) and Eclector Traps (light gray).

Discussion
Of the 21 families determined, 7 were not included in the previous checklist published in the "Atlas of Biodiversity" (Furlanetto 2002): Cerylonidae, Dryophthoridae, Eucnemidae, Laemophloeidae, Lissomidae, Monotomidae, and Zopheridae. Among these families, we found interesting species such as the Eucnemidae Melasis buprestoides which is an obligate saproxyilic beetle that develops in broadleaved forests both in the plains and in the mountains (Hůrka 2005) and is reported as Least Concern in the IUCN Red List (IUCN Red List, 2010). Another interesting species is the Anthribidae Eusphyrus vasconicus which was caught in the Alnus forests of the SCI "Boschi di Vaccarizza" and is rare and has been only recently reported in Italy (Tryzna andValentine 2011, Cornacchia andColonelli 2012).
Also, the Elateridae Calambus bipustulatus is rare for Italy as well as the 4 Ampedus species that are all classified as Least Concern in the IUCN Red List (IUCN Red List, 2010) and are closely associated with ancient and mature forests (Platia pers. comm.).
It is important to note the presence of other species included as Least Concern in the Red List of the IUCN and never previously found in the Park: the Cerambycidae Xylotrechus rusticus, the Cetoniidae Valgus hemipterus, the Elateridae Lacon punctatus, the Mycetophagidae Mycetophagus piceus, and the most abundant species of our study area, Litargus connexus.
Finally, it is interesting to underline the presence of two invasive species captured during the study: Cerambycidae Neoclytus acuminatus (Fabricius, 1775) and Xylotrechus stebbingi (Gahan, 1906). The latter was recently introduced into Italy but now is widely spread throughout Northern and Central Italy.
The period of field collection was planned in detail to provide a long and exclusive season of work to fully cover the reproductive cycle of a large number of beetles.
The combined use of two different types of traps significantly expanded the spectrum of insects capturable. The Eclector Trap caught a lower number of individuals and beetle species compared to Window Traps as is also described by other authors (Okland 1996, Bakke 1999, Schiegg 2000, Ranius and Jansson 2002, Wikars et al. 2005. However, this trapping method is more efficient in catching truly saproxyilic beetles (Alinvi et al. 2007), and the species were collected exactly where they developed.
The Trunk Window Trap captured a large number of insects also coming from the neighboring plots and/or forests. In this case, the site specific differences (i.e: amount of deadwood) disappeared and the differences became more evident at a landscape level such as habitat type.
Very few saproxylic species are listed in the EU Habitat Directive, but there are many others that should be considered in conservation plans for which we haven't had sufficient information about. The lack of knowledge on the ecology and distribution of these species make it difficult to establish criteria for their protection. Although we didn't find species listed in the Annexes of the EU Habitat Directive, some of the species found are locally threatened anyway because of their rarity, local distribution, and strong linkage to old forests. Among these species there are the Bothrideridae Bothrideres bipunctatus, the Cerambycidae Prionus coriarius and Xylotrechus rusticus, the Dryophthoridae Dryophthorus corticalis, the Eucnemidae Nematodes filum (with only 1 individual captured in Alnus unmanged forest), the Histeridae Aeletes atomarius and Paromalus flavicornis, the Laemophloeidae Cryptolestes duplicatus,, the Latridiidae Enicmus rugosus and Latridius hirtus, the Mycetophagidae Mycetophagus piceus, and the Zopheridae Colydium elongatum and Pycnomerus terebrans.
Thus, studies like this are important for increasing the ecological knowledge of forest beetle species and can provide a starting point for implementing management and conservation actions.