The plant landscape of Monte Pisano is characterized by a predominant forest component, with Pinus pinaster and Castanea sativa, of clear anthropic imprint. Another important component is constituted by dynamically advanced scrubs and woods of evergreen sclerophylls of natural origin, although often differently altered by the anthropic action and/or by fires, and dominated by Quercus ilex. Quercus suber is often found within holm oak woods, and – with lower frequency – inside the pine forests. Cork oak, in some cases, becomes dominant going to constitute the northernmost cork forests in Tuscany. The frequency of fires in Monte Pisano in the last decades seems to have led to an increase in Q. suber surface due to its known resilience to wildfires. The aim of this research is: a) to define the distribution of Q. suber in the area also in relation to repeated fire events in the past; b) to provide an updated characterization of these stands using a phytosociological approach; c) to identify stands and groups of trees that can be used as "seed forests" for post-fire forest restoration purpose, in relation to their marginal population characteristic. The study suggests a relationship between the spread of cork oak and the historical pattern of fires. This wide spread should be protected by forms of forest management unfortunately absent in this territory.

Forest fire, phytosociology, post-fire regeneration, Quercus suber, Quercion ilicis

The cork oak (Quercus suber L.) is a Mediterranean-Atlantic species with a large distribution in the Iberian Peninsula and in the north-western area of Morocco. From here it radiates along the coasts of the north-western Mediterranean up to the western and southern coasts of the Italian peninsula, including Corsica, Sardinia, and Sicily, while along the north-African coasts, it reaches Tunisia at the east (Barberis and Mariotti 1979; Blasi et al. 1997; Caudullo et al. 2017; Pignatti et al. 2017; Badalamenti et al. 2020). In Tuscany, it is widely distributed along the sub-coastal belt, with wide penetrations in the inland areas, from sea level to the hilly-mountain belts, where the climatic conditions allow it (Arrigoni et al.1999; Wikiplantbase #Toscana 2013) (Fig. 1).

Even with this relatively large distribution, significant forests of Q. suber – i.e. continuous wooded areas not less than 0.5 ha – can be found, in Tuscany, only in some areas. From south to north, in the hilly areas and rarely in the plain, between the Ombrone River and the Metalliferous Hills (Selvi and Viciani 1999; Arrigoni et al. 1998; Selvi and Valleri 2012; Angiolini et al. 2021), in the Island of Elba (Foggi et al. 2006), and on Monte Pisano (Bertacchi et al. 2004). For all other reports on the Tuscan territory, these are almost always stations of a few individuals or isolated trees.

In this context, two different types of forest are identified. The open formations, where the cork appears between the dominant tree species, if not exclusive, and the closed formations, where it is co-dominant with or dominated by the holm oak. In any case, the communities where Q. suber is present in a significant way have been ascribed to several associations and sub-associations of Fraxino orni-Quercion ilicis (Arrigoni et al. 1998; Selvi and Viciani 1999; Bertacchi et al. 2004; Foggi et al. 2006; Selvi and Valleri 2012).

Within this syntassonomic classification, the cork oak woods are mainly interpreted as durable phases due to the periodic passage of fires (Selvi and Viciani 1999) or in any case as a more or less temporary replacement of the holm oak wood due to fire (Arrigoni 1998).

However, it should be remembered that the presence and expansion of the Q. suber woods is also favored by the anthropic activity linked to the extraction of cork (Arrigoni et al. 1998).

Thanks to its great resistance to fire and aerial vegetative regrowth, Q. suber, as known from the Iberian peninsula and other areas of the Mediterranean, can often give rise to a "pyroclimax" community (Mètro 1975), i.e. a secondary succession in equilibrium with a regime of repeated fires (Pausas 1997; Silva and Catry 2006; Schaffhauser et al. 2012).

The territory examined in this work is historically affected by forest fires. These, exclusively of anthropic origin, have often been repeated in the same areas and with the same intensity, at a short distance of years (AIB 2022). This has resulted in a constantly changing plant landscape, giving rise to a mosaic of regressive dynamic stages and secondary succession.

From the Vegetation Map of Monte Pisano (Bertacchi et al. 2004), the areas recurrently affected by fire since the last 50 years were covered by pine forests of Pinus pinaster Aiton subsp. pinaster, by evergreen sclerophyllous scrubs with Q. ilex and by post-fire shrub vegetation. In this context, the cork oak has revealed a remarkable resilience by persisting in the areas that were repeatedly burned (Bertacchi and Borgia 2019), and in some cases, even expanding over time (Bertacchi 2022).

The aims of this research were: a) to define the current distribution of Q. suber in the Monte Pisano; b) update the map of cork oak areas; c) characterize the vegetation of the Q. suber communities by mean of the phytosociological approach; d) identify a possible correlation between the current extent of the species and the diachronic trend of the fires in the last fifty years on the mountain. In addition, we wish identify the populations and group of trees of Q. suber that can be used as locally native "seed forests" for post-fire forest restoration.

Figure 1. 

Distribution of Quercus suber L. in Tuscany (light grey circle: single occurrences /few individuals; dark gray circle: woods > 0.5 ha).

Based on our findings about the forest landscape of the Monte Pisano, the cork oak is distributed, with different density, only on the western and south-western sides of the mountain. Here, the environmental and soil conditions that are most suited to the ecology of the species occur. In fact, the microclimate of the area, given the close proximity to the sea, has Mediterranean characteristics with oceanic influences, in which the cork oak finds its climatic optimum. Furthermore, the prevailing lithology of the slope considered is given by acid and sub-acid quartzite rocks.

However, the distribution is not uniform and appears to be linked to different land uses or destructive events such as fires. In the first case, the mountain range that the cork oak would naturally occupy is historically covered to a large extent by terraced olive groves. Here cork oak can only be found as isolated individuals or in small rows at the edge of the terraces. The numerous and extensive areas reforested with pine trees from the eighteenth century until the second half of the last century, in surfaces unsuitable for the cultivation of the olive tree, have further reduced the range of Q. suber. This fact has reduced the possibility of spreading the cork oak, as noted in other contexts of Tuscany (Selvi et al. 2016). In this context, cork oak phytocoenoses of a certain size can only be found on the margins of these agro-forestry surfaces where, both from the toponymy and the analysis of historical aerial photos, their former and long-lasting existence can be confirmed. These phytocoenoses also represent those stations with more defined vegetational characteristics and with the most ancient individuals.

In the latter case, cork oak phytocoenoses with variable density are scattered throughout the southwestern slopes. Here, the maximum density of Q. suber is found in three areas where fires have been most frequent in the last 50 years (Fig. 6).

In these contexts, the phytocenotic characteristics of the cork oak stands seem to be diversified, both physiognomically and floristically, mostly by the time of recurrence of the fires. The type of vegetation pre-existing fire is, at least in the last 50 years, attributable to the forest of maritime pine. This, without excluding the presence on Monte Pisano of primordial and native presence of maritime pine (Targioni-Tozzetti 1768), can be attributed almost entirely to artificial plantations in historical times. In the foothills of the mountain, the pine replaced holm oak and ericaceous sclerophyllous scrubs and, at higher elevations, black hornbeam and other broad-leaved woods (Cosci and Giacobbe 1953). The current different phytocenotic characteristics would therefore seem to represent, in the majority of cases, different post-fire stages of a vegetation series attributable to the indifferent edaphic Tyrrhenian Italic series of holm oak (Cyclamino repandi-Quercetum ilicis sigmetum) or, in part, to the central subacidophilous Tyrrhenian series of the cork oak (Cytiso villosi-Quercetum suberis sigmetum) (Blasi 2010). In the investigated area, the dynamic trend of the areas hit by the fire seems to follow two paths. In the absence of new fires, a secondary succession that leads to mixed woods of holm oak and cork oak, while in the case of further fires, a series of secondary successions in equilibrium with a regime of repeated fires which maintains cork oak scrub. In this context, in microclimatic conditions consistent with the historical averages, a succession towards forest typologies with a prevalence of deciduous trees would likely occur, as observed in other Tuscan contexts (Spada 1993). Conversely, the occurrence of concomitant stress phenomena such as severe aridity and repetition of fires could lead to a degradation of the cork oak communities (Acacio et al. 2009). In our case study, the only two forest formations not affected by fire in the period considered seem to show stable characteristics of the evergreen sclerophyllous forest, albeit with frequent participation of deciduous trees such as Q. pubescens and F. ornus (Table 1: rels 4, 5, 6, 7, 8, 21, 22). All the other surveys highlighted, together with the constant presence and predominance of cork oak, aspects of scrub in different dynamic stages, in relation to the historical recurrence of the fires. The current extension of the species in the investigated area is therefore the result of environmental factors consistent with the ecology of the species and incidental factors (fire) favoring its diffusion.

If a detailed diachronic comparison between the past extension and the current one is not objectively possible, the overlap of its current distribution area and the area affected by fires in the last 50 years is nevertheless rather evident (Fig. 6). In any case, in the areas under Monte Verruca, which in the historical vegetation cartography were covered by post-fire scrub or pine forests (Bertacchi et al. 2004), today, after the last fires of 2008 and 2019, Q. suber is the most widespread tree species with detectable canopy.

The presence of the Habitat 9330 (EU directive habitats 92/43) in the Monte Pisano, is not clearly identifiable, although in some areas cork stands could be referred to the latter. The physiognomic and floristic characteristics of these cork oak communities have strong transitional characteristics caused by repeated anthropic fires, so as to consider these habitats as secondary habitats. In the stands for a long time no longer crossed by the fire, the forest tends to close, the herbaceous/ shrubby layer to decrease and to change the ratio of dominant tree species. Actually, all the more mature stages of cork forests seem to go in the direction of habitat 9340. In the perspective of forest restoration interventions on Monte Pisano, the native cork oak populations, partly unaffected by fire and partly survived to it, can be used as “forests for seed” of locally native germplasm. In these stands, a management of the forest capable of keeping its structure open is to be suggested. Furthermore, the widespread presence of Fabaceae shrub species such as Cytisus villosus and Genista sp. in the more recently burned areas could be considered for reforestation interventions.

Figure 6. 

Superposition of the main stands of Q. suber with the diachronic map of the fires (fifty years).

Table 1 – Rel. 4: 4845519.44-617186.84; rel. 21: 4843555.93-620408.09; rel. 22: 4843524.26-620485.56; rel. 7: 4845728.69-617320.87; rel. 5: 4845567.23-617172.71; rel. 6: 4845605.12-617216.81; rel. 17: 4845538.09-619195.59; rel. 18: 4845439.69-619188.81; rel. 15: 4846325.87-618121.09; rel. 16: 4846293.07-618038.53; rel. 25: 4843714.28-620620.15; rel. 8: 4846717.21-617211.16.

Table 2 – Rel. 29: 4843151.01-621047.13; rel. 9: 4846848.99-617508.63; rel. 10: 4846711.57-617657.93; rel. 23: 4843358.00-620691.97; rel. 32: 4840178.89-622494.59; rel. 24: 4843305.41-620734.39; rel. 35: 4840225.26-622844.08; rel. 36: 4840211.12-622688.56; rel. 30: 4840987.59-622248.59; rel. 31: 4840826.98-622315.89; rel. 33: 4840176.06-622587.90; rel. 34: 4840281.24-622777.35.

Table 3 – rel. 19. 4844336.92-620327.77; rel. 26: 4843554.24-621047.69; rel. 28: 4844066.03-621082.18; rel. 20: 4844334.66-620369.06; rel. 13: 4846413.53-618390.29; rel. 27: 4844003.26-621061.82; rel. 11: 4846613.73-618119.96; rel. 3: 4845643.57-616979.29; rel. 37: 4840149.62-623359.98.