**1. Introduction**

The olive tree can be considered the most symbolic tree of civilization and a part of the anthropized Mediterranean landscape [1]. Exploited at least since the Mesolithic [2] and cultivated for the production of oil at least since the Bronze Age in Sicily [3,4], it has a wide distribution in all countries bordering the Mediterranean, with around 800 million individuals [5,6]. Evidence of mythology, history, and literature attest to the grea<sup>t</sup> importance of the olive tree and its oil in the trade, food, and customs of Mediterranean populations, starting with the olive tree as the protector tree of the city just founded by Athena and mentioned among the most precious trees by numerous Jewish, Greek, and Roman sources [6]. It is a very long-lived plant, with very slow growth, able to bear fruit for several hundreds of years, assuming extraordinary shapes and sizes over time and contributing to modern genetic diversity [7].

The use of the wild olive dates back to the Israeli region in the Epipaleolithic [4]. It is probably from primitive cultivation located in the west of Iran and the south of the Caucasus that the irradiation to other geographical areas and the differentiation of the

**Citation:** Schicchi, R.; Speciale, C.; Amato, F.; Bazan, G.; Di Noto, G.; Marino, P.; Ricciardo, P.; Geraci, A. The Monumental Olive Trees as Biocultural Heritage of Mediterranean Landscapes: The Case Study of Sicily. *Sustainability* **2021**, *13*, 6767. https://doi.org/10.3390/ su13126767

Academic Editor: Pietro Santamaria

Received: 18 May 2021 Accepted: 11 June 2021 Published: 15 June 2021

**Publisher's Note:** MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.

**Copyright:** © 2021 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

different cultivated varieties began [5]. It is believed that the cultivated olive tree (*Olea europaea* L. var. *europaea*) is derived from the refinement of the wild one (*Olea europaea* var. *sylvestris* (Mill.) Lehr), which is spontaneous throughout the Mediterranean basin [8] and with which it retains considerable genetic affinities [9], although its origin is still much debated [10]; however, it is no coincidence that the aspect of the abandoned olive tree tends to regress toward that of the wild olive tree [11]. The distribution of the olive tree, in fact, is almost superimposed on that of its wild ancestor, representing one of the characteristic elements of Mediterranean sclerophyllous vegetation [8]. According to Zohary and Hopf [9], within the Mediterranean countries, the olive tree was one of the first fruit plants to be domesticated, perhaps as early as the 5th millennium BC, as evidenced by the several structures for the pressing of olives found in the Chalcolithic age in the Jordanian area [12].

The olive varieties we know today would therefore be the result of an ancient selection process [13] by Syrian and Palestinian farmers and probably also those from the vast area extending from the Southern Caucasus to the Iranian highlands, starting from the wild olive tree, widespread in that time period but not very usable for food purposes due to the spinescence and small drupes and their being poor in oil, to cultivars rich in oil and without thorns [14–16].

The relation between humans and olive trees in Sicily has a long story. Beyond the previously cited remains from Grotta dell'Uzzo, olive tree wood has been exploited in Eastern Sicily since the end of the Paleolithic [16]. According to the natural sequence of Pergusa lake, *Olea* sp. experienced an expansion starting from 7200 BP (Middle Neolithic) [17], but it is unlikely that it was due to its early cultivation. Archaeobotanical data confirm that olive tree wood and probably its fruits were used during the Bronze Age, 2nd millennium BC, despite missing carpological data [18–20]. For the Greek colonies such as Selinunte (7th century BC), the olive tree was considered a symbol of peace, wisdom, and prosperity for the various uses to which the oil was intended. Carpological data are scarce, probably due to the extremely low record of archaeobotanical remains for these phases; the only exception is the city of Camarina [21]. According to literary sources, the farmers of Selinunte became a point of reference in the oil trade in the Mediterranean. They cultivated and propagated the olive tree in the valleys and in the fertile lands of the hinterland, producing oil, as evidenced by the findings of rudimentary mills dating back to the fifth century BC [22] and exporting it, as the city of Akragas, to the Phoenicians colonies of Northern Africa [23].

It is evident that this tree constituted a preponderant and highly characterizing element of the ancient Sicilian agricultural landscape, also according to the literary sources. Thucydides (Book VII, 81, 4), speaking of a village south of Syracuse, called the Polizelo enclosure, where the Athenians stopped briefly in retreat, gives us the opportunity to imagine the olive fields delimited in "enclosures" by low walls of dry stones, as they are still today for the needs of sheep farming. One significant document with some valuable information on the olive tree in antiquity is the Tabulae Halaesinae, a Hellenistic description carved on two stone tablets of the land of Halaesa, an ancient city near the modern village of Tusa (Messina). Ancient olive trees are raised to the role of natural monuments through the marking of the Halaesian monogram engraved on the bark as a marking boundary sign [24]. In the Tabulae, the importance and predominance of olive cultivation for the economy of that territory come out, also supported by the presence of special "nurseries" (*elaiokomion*) [25]. During the Roman Empire, the exploitation of Sicilian oil together with other food resources was slowly replaced with the use of the island as a bridge for the import of Northern African products [26]. Finally, during the Middle Ages, its presence in the hilly Sicilian landscape seems quite spread, with some exceptions, especially in the Islamic areas [27–29].

Today the olive tree, together with wheat and vines, represent the "Mediterranean triad" of traditional agriculture [30]. In the Sicilian agricultural landscape, dry (nonirrigated) olive groves are widespread in pure plantations, with more or less irregular spacing, or in "mixed cultivation" systems, together with carob and almond trees.

The centuries-old olive trees and, more generally, all monumental trees, with their longevity and considerable size, certainly represent a sign that is not negligible for the purposes of a better understanding of the territory that hosts them and of the society that wanted them to be preserved. The attention to monumental olive trees is linked to the most up-to-date concepts of "istorical ecology" for the interpretation of the traditional rural landscape, in which the historical-anthropological components are intimately connected to the natural ones. As a matter of fact, as cultivated plants, olive trees are anthropogenic elements of the landscape, and, thanks to their longevity, they have become a source of historical information on the use of the territory. They are the only cultivated plants that tell the story of the Mediterranean landscapes through the Anthropocene and represent a "cultural heritage", like some stone monuments. Having evolved over the centuries, the olive tree landscapes represent a tangible example of sustainable land use [31]. The recognition of ancient and notable trees and historic orchards as elements of cultural heritage is widely accepted (see, e.g., www.english-heritage.org.uk), although, as they are living monuments, we believe it is more appropriate to consider trees as elements of the "biocultural heritage" [32].

While some research has focused on the role of olive groves in the Mediterranean landscape e.g., [33–35], less emphasis has been placed on the cultural/biocultural value of single monumental olive trees that dot the landscape.

Considering the importance of secular olive trees not only from a cultural, environmental, and scientific point of view, as well as for the precious genetic heritage of which they are depositories, in 2003, a survey project was started in Sicily in order to acquire significant elements for the documentation, protection, and enhancement of this plant heritage [36,37].

This work reports the results of the survey of monumental olive trees conducted in Sicily and discusses their value in terms of "biocultural heritage" and the importance they play in the interpretation of the historical stratifications of the landscape.

### **2. Materials and Methods**

### *2.1. Study Area*

Sicily is the largest Mediterranean island, with an area of approximately 25,500 km<sup>2</sup> and about 1000 km of coastline. The island has different geological characteristics, which have shaped different landforms with an elevation ranging from sea level to 3340 m (Mount Etna). The territory is hilly in the central and southwestern parts (approximately 61.4%), mountainous, especially in the northern and eastern parts (24.5%), and 14.1% consists of alluvial plains [38].

According to Bazan et al. [39], Sicily is divided into 25 bioclimatic belts (thermotypes and ombrotypes) from thermomediterranean semiarid to cryo-mediterranean hyperhumid. This grea<sup>t</sup> variety of environmental conditions and its complex paleo-geographic and human history make the island one of the Mediterranean biodiversity hotspots.

Agricultural systems are widespread and are structured as highly diversified landscape mosaics (arable lands and extensive herbaceous crops, vineyards, olive groves and dry cultivation mosaics, orchards, built-up areas, etc.), which are significant containers of agrobiodiversity.

Olive groves create diffused semi-open landscapes compared to other tree crops, especially along the marginal hilly areas and at the base of the mountainous areas [40]. The cultivation of the olive tree currently has about 18 million plants in Sicily and contributes considerably to the characterization of the physiognomy of the region's agroecosystems, with particular reference to the hilly ones, where 65% of the olive groves exist, and to the mountain ones, where the traditional olive groves represent 17% of all groves [41]. With an area of 157,891 ha [42], equal to 6.1% of the regional territory, this cultivation plays an important role.

### *2.2. Data Collection*

The survey covered the entire Sicilian regional territory and the selection of the most significant specimens, chosen for their "monumentality" aspect, mainly took into account the parameters inherent to the measurement of maximum circumference, measured at 1.30 m from the ground (for appropriate comparisons with other individuals), height, development, crown width, and presumed age. This information was also integrated by considerations relating to the historical, naturalistic, and landscape value of the individual plants.

For the survey, the research group also made use of the collaboration of the technicians of the Operational Sections of Technical Assistance (SOAT) of the Regional Department of Agriculture, Rural Development, and Mediterranean Fisheries, located in the territory, which helped to report to the authors the presence of individuals with the characteristics of monumentality.

The research methodology was chosen in order to maintain the methodological continuity with previous surveys on monumental trees carried out in Sicily [25,36,42,43]. For the survey of monumental individuals, the survey form proposed by Schicchi and Raimondo [25] was used; it is made up of various items, listed below and contextually explained to summarize the methodology used for the acquisition of the information data:


In the attribution of age, both the growth features of the species and the fertility conditions of the site where the monumental olive trees were found were considered.

