Introduction

Starting from the Middle Ages, chestnut cultivation became a staple resource for fruit and timber production in several European countries, where the chestnut was cultivated up to its ecological limits (Pitte 1986). This cultivation greatly influenced the lifestyle of the mountain populations, giving origin to the so-called “chestnut civilization” (Gabrielli 1994; Arnaud et al. 1997; Conedera et al. 2004).

The traditional European chestnut civilization declined at different times in different countries. The first decline corresponds to the climatic cooling of the eighteenth-century Little Ice Age that caused frost damage on chestnut orchard trees at the exposed sites. The improvement of agricultural cultivation techniques combined with the introduction of alternative crops from abroad (maize, potatoes)—by allowing a greater production of calories with shorter rotation times—also contributed to the progressive substitution of chestnuts as a staple food (Conedera and Krebs 2008). After the mid twentieth century, the depopulation of the mountain countryside (Bonous 2002; Conedera and Krebs 2008) brought about an accelerated decline in chestnut cultivation. At the same time, the appearance and spread of chestnut blight (Chryphonectria parasitica [Murr.] Barr) produced severe damage, threatening the chestnut cultivation, as had already occurred in North America (Biraghi 1946; Griffin 2000). Moreover, ink disease (caused by Phytophthora cambivora [Petri] Buism.), which appeared in Apennine chestnut forests at the start of the twentieth century (Petri 1918), showed a resurgence in recent decades (Vettraino et al. 2005). In many cases, these factors led to both the complete abandonment of traditional chestnut orchards and a rapid post-cultural evolution toward mixed stands based on climate, soil, stand density, pathogen incidence, and time since abandonment (Mondino 1991; Paci 1992; Romane et al. 1995; Arnaud et al. 1997; Paci et al. 2000; Conedera et al. 2001). In other cases, chestnut orchards were coppiced or planted with conifers in order both to control the spread of diseases (Biraghi 1955) and to overcome the decline in economic values, respectively (Conedera et al. 2004). Similarly, coppice stands underwent either an extension of the traditional rotation time or total abandonment (Conedera et al. 2001; Manetti et al. 2001). Figure 1 shows a general framework illustrating the driving factors which affect the chestnut stand dynamics.

Fig. 1
figure 1

Conceptual framework of factors affecting chestnut stands. Arrows indicate one way relationships, segments two way

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The disappearance of the traditional chestnut groves represents a cultural as well as an ecological loss that may be considered equivalent to the consequences of the natural reforestation of abandoned fields and pastures. In European chestnut areas this disappearence represents one of the most significant changes affecting biodiversity over the last 60 years (Piussi and Pettenella 2000). This has also been recognized by the European Community Natura 2000 network (EU Council Directive 1992), which declared both the Castanea sativa-dominated forests and long-established chestnut plantations with semi-natural undergrowth important habitats (9260 Castanea sativa woods) for biodiversity conservation (European Commission 2007). This is of particular relevance for Italy, where chestnut woods still dominate the low and middle mountain landscape both in the Southern Alps and the Apennines.

In the meantime, some of the factors that caused the abandonment of chestnut cultivation have changed. Because of the natural spread of chestnut blight hypovirulence (Turchetti and Maresi 2000) and thanks to increasing market prices for their top quality fruits (marrons) and for their derived products with high added values, chestnut orchards and woods are again playing an economic role in some parts of the European mountain regions (Pettenella 2001). The cultivation of high-value chestnut products (fruit or timber) is being intensified in the best chestnut-growing areas, new plantations are being created on potentially good chestnut sites, and traditional old orchards are being restored as part of a multipurpose landscape (Bonous 2002; Conedera et al. 2004). To this aim, the basic knowledge of the factors affecting both the structure and the biodiversity in managed and unmanaged chestnut groves is needed.

Changes in land use, environmental diversity, socioeconomic scenarios, and the impact of plant diseases are the potential driving factors for the present species composition in chestnut stands.

We analysed these factors in the chestnut orchards of Mt. Vigese, a Site of Community Importance (SCI) (IT4050013) in the Northern Apennines, which may well exemplify similar situation throughout the main European chestnut countries.

Using a multi-scalar, multi-temporal, and multi-source approach, our analysis aimed to:

  • establish a general understanding of the interaction among changes in land use, biodiversity, socio-economic factors, and plant diseases;

  • characterize the structure and typologies of the present chestnut groves;

  • identify suitable future management options in protected areas such as SCIs.

Methods

Study area

Mt. Vigese SCI (IT4050013; 617 ha), lies in the Northern Apennines (lat. N 44° 12′ 46″; long. E 11° 05′ 38″) with an altitudinal range of 495-1089 m a.s.l. (Fig. 2). In 1995 this area became part of the Natura 2000 network and in 2004 it was also classified as a Special Protection Area (SPA) within the Biogeographic Continental Region. The lithological substrate consists largely of sandstone and marl which “float” on a vast clay base. The area, in general, is subject to landslides, which occurred notably in 1852, 1903, and 1950 (Mazzuoli 1903; Biagetti 1997).

Fig. 2
figure 2

View of the Mt. Vigese SCI (IT4050013; Lat. N 44° 12′ 46′′, Long. E 11° 05′ 38′′) and its long-established orchards (right)

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Mixed oak woods largely dominate the vegetation (Pezzi et al. 2005). Long-established chestnut orchards and many chestnut coppices are widespread at an altitudinal range between 495 and 980 m. This Habitat of Community Importance (9260 Castanea sativa woods) is characterized by acidophilic undergrowths with Luzula (L. pedemontana, L. sylvatica, L. forsteri) and Geranium nodosum in the dampest areas. Other Habitats of Community Importance within the SCI (Pezzi et al. 2005; Regione Emilia Romagna 2007) are: 6210 semi-natural dry grasslands and scrubland facies on calcareous substrates (Festuco-Brometalia); 6110 rupicolous calcareous or basophilic grasslands of the Alysso-Sedion albi; 5130 Juniperus communis formations on heaths or calcareous grasslands. From a biogeographic standpoint, a Quercus ilex population on sandy outcrops (Cocconi 1883) is of particular interest as it is included in the habitat 9340 Quercus ilex and Quercus rotundifolia forests.

Land use reconstruction

Data sources on land use consisted of 1:2000 scale geometric-parcel-based cadastres (1807, 1924), panchromatic nadir aerial photographs (1954, 1971, 2000), and a vegetation map (Pezzi et al. 2005) based on the phytosociological approach as proposed by Braun-Blanquet (1964).

The earlier data source was the 1807 revised version of the Boncompagni cadastre (BC) dating back to 1780–1835. This is the first professionally prepared survey, which provides a fairly reliable picture of local land use (Giacomelli 1987; Salterini and Tura 1995). The 1924 maps belong to the Cessato Catasto Terreni (CC) and represent the original geometric-parcel-based cadastre (Bracchi 1956), first established in 1886 for the whole of Italy. Cadastral maps were scanned at 600 dpi and georeferenced by using a number of Ground Control Points (GCPs) recognizable on cadastral maps from the most recent digital orthophotos (IT2000 flight dating back to 1998–1999; 1 m resolution). Selected GCPs produced a co-registration error of about 2 m; bilinear transformation was used as a resampling method. Maps were mosaiced and a vector layer was created by tracing the parcel limits in ArcGIS 9.2 (http://www.esri.com/). The land use of each parcel was identified from the Land Registry (Brogliardi for BC, Tavole censuarie for CC).

Aerial photos from 1954 and 1971 were digitalized (800 dpi) and orthorectified with an orthogonal projection of all the points in the image to a reference surface in order to correct all types of distortion (Jensen 1996; Novak 1992, see Pezzi et al. 2007 for details). Images were visually interpreted and simultaneously digitized with the ArcGIS software.

The comparison of the oldest cadastral maps to the most recent surveys requires a common classification system of land cover units (Dunn et al. 1991). We adopted the CORINE Land Cover legend (European Environment Agency 2000). Except for cadastral maps, where chestnut orchards and mixed oak coppices are distinct, the forest vegetation cover was detailed (Table 1). The change direction was obtained by overlaying the layers of different years.

Table 1 Land use/land cover evolution 1807–2005
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In order to test the influence of topographic features on the land use change (see abiotic template in Fig. 1) a Digital Terrain Model (DTM) of the area was implemented by using contours acquired from 1:5000 Regional Technical Cartography (CTR) of the Emilia Romagna Region. Then slope, elevation, and aspect were derived and overlaid with land cover maps.

For the evaluation of demographic and agroforestry trends in a broader context (see socio-economic factors in Fig. 1) we considered the following statistical data referring to the hill and mountain areas of the province of Bologna:

  • Resident population according to the Italian censuses: starting from 1861, every 10 years up to 2001 (ISTAT 1994, 2003). Data from the municipalities of Grizzana and Camugnano, in which the SCI is situated, were also extracted.

  • Annual surface area (ha) of chestnut woods (orchards and coppices). Local data (ISTAT and the Official Gazette of Italy) were available for coppices from 1947 to 1977, as well as for orchards from 1929 to 1993 with some gaps. The most recent data (2003) derives from a forest map of the province of Bologna.

Characterization of chestnut stands

Twenty-eight randomly selected chestnut forest plots (20 × 20 m) were surveyed by using a design-based probabilistic sampling approach from points placed on a 250 m × 250 m grid (Chiarucci and Bonini 2005). In the summer of 2005, the selected plots were located with a high precision GPS and the total list of woody species was collected. Furthermore, DBH was measured for woody individuals with DBH > 3 cm; the type and frequency of blight infections (Cryphonectria parasitica) and the presence/absence of ink disease (Phytophthora spp.) were also noted.

Blight incidence was evaluated by the ratio between healing and healed cankers compared to virulent and intermediate ones (Turchetti and Maresi 2000; Turchetti et al. 2008). Lethal blight infections were classified as recent where dead foliage persisted on branches and old where branches were already debarked. Trees or stumps killed by ink disease were classified as old (tissues very degraded) or recent (dead foliage, bark and tissue still present or still suffering trees) attacks.

Statistical analyses at the plot level were carried out using the Vegan package (R version 2.9.2.). Dominant woody species basal areas were analyzed with non-metric ordination (Non-Metric Multidimensional Scaling, NMDS) in order to detect the main features and trends of the plot structure. Following Chiarucci and Bonini (2005), we considered as dominant the species with at least 25% of frequency and 5% of total basal area in each plot. Information on topographical features (elevation, slope, aspect), ink disease, continuity of management, landslides, and presence of orchard vestiges were fitted as variables onto the ordination in order to obtain their correlation to species distribution.

Results

Land use reconstruction

Table 1 and Fig. 3 show changes in land use in Mt. Vigese SCI.

Fig. 3
figure 3

Changes in land use/land cover of Mt. Vigese SCI, in the last two centuries (1807–2005). Classification follows CORINE Land Cover nomenclature. Further explanations in the text

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The 1807 map shows that chestnut orchards with agricultural areas and herbaceous vegetation (mainly pastures) cover the largest areas while artificial surfaces are scarce. This map is closely related to extensive human farming activities.

In the 1924 map, the area of chestnut orchards is almost unaltered in extent (24%), with few changes in their distribution. Most changes derive from the extensive landslides registered in 1852 and 1903 (Mazzuoli 1903), which caused the destruction of some orchards and their replacement by open spaces. Unfortunately, there is some confusion between woods and scrubs and herbaceous vegetation cover, probably as a result of the fuzzy criteria used to evaluate the difference between abandoned and wooded pastures.

The largest extent of chestnut orchards was reached in 1954 (151 ha). In the following years the orchard cover decreased to 48 ha in 1971 and to 6 ha in 2005.

Starting from 1954, the chestnut orchards decrease corresponds—in both area and distribution—to a chestnut coppice increase, reaching a cover of 130 ha in 2005. Chestnut orchard abandonment and/or coppicing were similar in all the classes of slope, aspect and elevation although orchards at the highest elevations or on the steepest slopes had first been coppiced and then disappeared.

After the first substantial decrease shown on the 1971 map, a second significant decrease in the extent of chestnut orchards is revealed by the 2005 survey. The few remaining chestnut orchards lie in the more accessible and less steep areas. Small groups of grafted trees for domestic use are found near houses. In general, mixed oak woods increased in the abandoned fields and pastures. It should be noticed that no dead trees or damaged crowns were identified by aerial photos throughout the surveying period and forest types.

The trend of population density (Fig. 4) is almost in line with the temporal pattern of the landscape dynamic and shows: a peak in the mid 1930s followed by a decrease starting in the late 1930s, which abruptly accelerated during the second half of the twentieth century. In the last 20 years (1981–2001) resident populations changed in different ways: Camugnano remained substantially stable while a marked increase was recorded in Grizzana as well as in the whole mountain area of the Province.

Fig. 4
figure 4

Trend of population and chestnut woods in the SCI (above) and in a broader context (province of Bologna)

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In the 1930s, both the population size and chestnut orchards reached their greatest extent in the whole province of Bologna. From 1947 until the late ’70s there was a steady population decrease, but the area of the chestnut woods remained unchanged.

Figure 4 clearly shows that when chestnut orchards decrease, coppices increase. However, the percentage of coppices is not equal to that of chestnut orchards lost in the same period, thus indicating that in some cases chestnut orchards were abandoned and naturally reverted to mixed forest stands.

Disease incidence

Chestnut blight was observed in every plot, but damage was limited. Healed and healing infections made up 84% of the 1850 cankers observed on chestnut trees with a further 11% of intermediate, non-lethal infections. Only 5% of attacks were lethal, but they concerned only branches or small and depressed sprouts. The prevalence of healed and healing infections was clear in all but one plot (plot 26), where intermediate infections predominated, together with a low number of normal cankers. Old attacks on branches were found in 14 plots while new lethal infections were found in 9 plots: in all but one (plot 9) they affected only 1 or 2 branches or small and depressed sprouts.

Stumps killed by ink disease were observed in 9 plots. In two plots there was evidence of previous attacks, and just initial symptoms in one. In 6 plots old and recent damage was evident. Only one or two infected stumps in each plot were evident: however, in the whole area, including all 28 plots, two larger issues affecting several trees were observed during the surveys.

Forest structure and woody species

In total, 3746 stems belonging to 31 different woody species were sampled (Table 2): more than 50% (2014) were Castanea sativa. Ostrya carpinifolia has 592 stems (16%), Corylus avellana and Fagus sylvatica over 200, Fraxinus ornus, Quercus pubescens, and Robinia pseudoacacia over 100. For the 1.1 ha sampled area, the total basal area is 52.57 m2: 67% is covered by Castanea sativa and 12% by Ostrya carpinifolia. Remaining species (with the exception of Fagus sylvatica, Fraxinus ornus, Quercus pubescens, and other few species) cover no more than 0.3%.

Table 2 Total number of stems, basal area, and frequency per plot of the woody species in the 28 plots considered
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The number of stems (stems plot−1; Table 3) ranges between 21 and 232: most of the plots (22) show a stem density >100 (about 40% more than 150); only two plots more than 200. Basal area ranges from 0.86 to 4.90 m2 plot−1. As to Castanea sativa, the number of stems ranges from 5 (plot 8) to 190 (plot 20), while basal area from 0.08 (plot 16) to 4.58 m2 plot−1 (plot 21).

Table 3 The topographic and chestnut stand features considered in the 28 plots sampled
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Castanea sativa is the dominant species in 24 plots (Table 3), in some stands with Quercus pubescens, Prunus avium, Ostrya carpinifolia, and Robinia pseudoacacia. Four plots are clearly dominated by Ostrya carpinifolia or Fagus sylvatica. Table 3 shows also that all the plots but two were coppiced after 1954.

Figure 5 shows the distribution pattern of plots following NMDS. Most plots are along the first axis; they are chestnut coppices with a different Castanea sativa content. Along the first axis the presence of Castanea sativa increases (see Castanea group of plot in the first positive semi axis), while Ostrya carpinifolia, which indicates an evolutionary trend toward mixed deciduous stands, decrease. Plots 2 and 28 have almost completely ousted Castanea sativa. Coppices with Robinia pseudoacacia (plot 4 and 5), Quercus pubescens (plots 7, 9, 11 and 26), or Fagus sylvatica (plot 8 and 16) are clearly separated, in accordance with their different ecological features and the altitude. Q. pubescens is accompanied by shrubs, indicating more light availability or xeric conditions (e.g. Cytisophyllum sessilifolium, Cytisus hirsutus, Genista pilosa, G. germanica, and Teucrium chamaedrys), while R. pseudoacacia is accompanied by Sambucus nigra, Rubus spp., Clematis vitalba, indicating disturbance. Fagus sylvatica plots are located at highest altitude and have almost completely ousted Castanea sativa. In addition, the NMDS clearly distinguishes the abandoned chestnut orchard (plot 21) from the cultivated ones (plot 23).

Fig. 5
figure 5

NMDS (Non-Metric Multidimensional Scaling) Ordination diagram of basal areas showing the gradient and the correlation to topographical features (elevation, slope, aspect), ink disease, continuity of management, landslides, presence of orchard vestiges. Vectors show the direction of the gradient, length of the arrow is proportional to the correlation between the variable and the ordination. Circles indicate group of plot and the main invading tree species (Ostrya carpinifolia, Robinia pseudoacacia, Quercus pubescens, Fagus sylvatica). Stress: 9.738; P = plot

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Among the environmental factors considered, only the elevation and slope have a significant relationship with the changes in species composition.

Discussion

Chestnut forest dynamics on the Mt. Vigese SCI are clearly described by the multi-temporal approach based on highly comparable data sources. In addition, medium–high resolution maps allowed the downscaling of the multi-scalar approach, from the landscape to the stand.

Figure 6 summarizes both the historical evolution of chestnut forests in the SCI Mt. Vigese and its relationship with the different constraints identified. The observed trend (1807–2005) can be considered a good example of the general trend in the Northern Apennines chestnut forests: a continuous increase in orchards through the first half of the twentieth century followed by a sharp decrease up to the present time (Agnoletti 2010). Factors shown by the Fig. 6 can be considered almost representative for the most of the Italian districts and applicable to other Mediterranean mountain areas (Pitte 1986; Conedera et al. 2004). However, local factor, especially competition with other more productive coltures (as in France) could have played an effective role (Fauve-Chamoux 2000), but their influence seem reduced in the mountain context as that examined in this work: chestnut forests had and have no economical alternative.

Fig. 6
figure 6

Summary of historical evolution of chestnut woods within the Mt Vigese SCI and its relationship with the different constraints considered

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In our study area most chestnut orchards have been coppiced quite abruptly since the late 1950s. This is very much in line with a general trend in the whole Italian Peninsula due to the belief that chestnut orchards had no chance of surviving when attacked by the chestnut blight, whereas managed coppice stands displayed an increase in resistance after several coppicing (Biraghi 1955). What Biraghi very likely observed in the chestnut coppices of first introduction of the disease were the first signs of hypovirulence, that he interpreted as an increased chestnut resistance to the blight (Biraghi 1955). According to the eminent pathologist and researcher, the best way to preserve chestnut stands from disappearing was the repeated coppicing regardless of the type of forest (orchard or coppice). He therefore suggested (and the National Forest Service applied) the systematic coppicing of chestnut orchards to preserve chestnut germoplasm and related forest services (Biraghi 1955). This may be the main reason why people just proceeded to a coppicing before or instead of abandoning stand management where the coppicing of chestnut orchards was related to some local economic benefits (such as money obtained from tannin production). As a result, very few big trees are present in the remaining chestnut woods and very few orchards still lie within the SCI under consideration.

Chestnut is still dominant, thus confirming that surveyed areas are an optimal habitat for this species. Over the past 50 years, Fagus sylvatica and Ostrya carpinifolia almost replaced Castanea sativa only at the edge of chestnut area. Fagus sylvatica, Ostrya carpinifolia, Quercus pubescens and Robinia pseudoacacia (these last limited only in disturbed areas) are the invading tree species in our chestnut stands. However, our study shows that in the study area Ostrya carpinifolia may be locally considered the main indicator of Castanea forest dynamics toward mixed deciduous woods. Although the two species show different ecological needs in term of soil acidity and lime content of the soil, the particular characteristics of the sandstone and marl substrate present in the study area allow the coexistence of both species. Elevation and slope seem to act as the most effective site factors. It is likely that they have been immediately affecting the choice between management and abandonment.

It is worthy of note that all the original orchards in this area consisted of local varieties used for chestnut nut and flour production, mainly for self-sufficiency or to exchange with other products. Owners were discouraged from maintaining this cultivation because of its lack of profitability, which can in no way compare to the income possible from wood and timber sales. Probably, parts of nuts were commercialized and could be involved in commercial channel towards cities and foreign countries, but the bulk of the production and especially flour, as everywhere on the Apennines, just covered the family needs. Still now, flour is a secondary product and orchards with flour varieties are mainly abandoned or coppiced due to the very high production costs with respect to the market prices (Pettenella 2001; Conedera et al. 2004). As a consequence, most restoring activities of productive orchards are strictly related to possibility of cultivating the high quality varieties of “marrons”, mainly for the fresh consume (Conedera et al. 2004).

The demographic trend seems to have been the main driver of the landscape changes over the last two centuries: chestnut woods were affected in extent, management, and structure. Population increase meant more orchards; its decrease meant either its abandonment or replacement by coppices. The recent slight mountain repopulation observed in both municipalities considered, as in some other Apennine areas, has not affected chestnut cultivation: the incoming population is not involved in woodland ownership and has no economic interest in chestnut cultivation. Most of the new inhabitants are either from cities or from different cultures and traditions. They have no links to the “chestnut culture” and they cannot contribute to the related cultural landscape. Only one single coppice conversion into a new orchard for “marrons” chestnut production was observed in the study area! It appears highly improbable that all the former orchards will be recovered in the near future. The maintaining of the few old grafted trees close to houses is more plausible.

The predominance of hypovirulence in all the surveyed plots is clear, and the small number of old attacks observed suggests that, probably, the equilibrium between host and parasite was reached early on. At present, in the area considered as well as in the whole Italian chestnut range, blight is not a threat to chestnuts and does not seem to influence forest changes, except as a secondary agent during periods of stress (droughts or windstorms or other climate stress), as observed by Davini et al. (1998) and Turchetti et al. (2008). The greatest negative impact on the landscape dates back to the 1950s, when chestnut coppicing was extensively pursued in order to constrain the blight spread (Biraghi 1946, 1953). It is important to note that oldest trees survive epidemic outbreaks, thus confirming the early appearance of hypovirulence also in this area. There was no historical record of ink disease in the area and, like blight damage, it did not show up in 2003 aerial photographs. It is suggested that only small but widespread attacks appeared during the 1990s, as in other areas of the Apennines (Turchetti and Maresi 2000; Vettraino et al. 2005), without immediate and significant effects on chestnut presence. A more effective action might manifest itself in the future, especially in the two largest foci that were observed in the area. The recent appearance of the chestnut gall wasp (Dryocosmus kuriphilus Yasumatsu) in the Northern Apennines could act as a new disturbance factor but its effects are not yet known or foreseeable (Graziosi and Santi 2008). In addition, dated and recent chestnut parasites and diseases may interact increasing the pressure on the phytosanitary conditions of the stands (Turchetti et al. 2010).

In the near future, the management scenarios may be summarized as follows either for Mt. Vigese or for most of chestnut woods on Mediterranean mountains:

  1. 1

    maintenance of chestnut coppices by regular coppicing. This solution requires a market for chestnut wood. Up to now, the absence of recent coppiced area suggests that no or limited economic values are involved in this kind of product.

  2. 2

    natural dynamics from abandoned coppices to mixed woods. At present, the sampled plots are mainly old abandoned coppices. Increasing changes in the species composition of the abandoned coppices toward mixed oak woods can be foreseen but, as shown by our data, this process has not yet begun and seems to be a long-term process.

  3. 3

    conversion to new orchards—this scenario might involve only small areas, as it is connected mainly to the local population size as well as to market development. In any case, the preservation, as well as the recovery, of big old grafted trees may greatly affect the stability in the local biodiversity.

The Natura 2000 programme offers new resources for maintenance of Mt. Vigese old chestnut woods in the near future. However, without a change in the social and economic context, different appropriate management choices must be sought.

As in many other chestnut areas of Europe, the most promising strategy for enhancing conservation and active management of the chestnut forests includes their marketing as a multipurpose forest type where outputs are not only organic fruits and fruit-derived products, as well as woody products, but also other non-woody products (honey, mushrooms, herbs, etc.) as well as the chestnut landscape, their biodiversity, cultural heritage and eco-touristic potential.