introduction - Ecologia Mediterranea

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Phenology and growth of Quercus ilex L. in different environmental conditions in Sicily (Italy) Phénologie et croissance du chêne vert (Quercus ilex L.) sous différentes conditions environnementales en Sicile (Italie) Tommaso La Mantia 1, Sebastiano Cullotta & Giuseppe Garfì 1. Corresponding author. Dipartimento di Colture Arboree, Università degli Studi di Palermo, Viale delle Scienze 11, 90128 Palermo, Italy tel +39 091 423398, fax +39 091 6521098, email agrofor@unipa.it Summary Phenology and growth of Quercus ilex L. in four different sites in Sicily were analysed over a period of two years, with the aims to contribute at the knowledge of ecology and adaptive plasticity of this species. The following aspects were considered: i) sprouting, ii) flowering, iii) fruiting, iv) shoot growth, v) leaf longevity, vi) leaf area. The results showed a variability among the four investigated sites. A precocity for most of the phenological phases, a higher growth and a polycyclic growth were observed only at Mt Pellegrino, the most “oceanic” and hottest site among the investigated ones. Indeed, such features are likely further enhanced by the climatic peculiarities of that site, such as the high atmospheric moisture and the mild autumn. According to our data, Quercus ilex globally exhibits a notable adaptive ability to different environments. In the same time, its response at Mt Pellegrino is consistent with the assumption that this species originated in a tropical-type climate. Key-words Ecophysiology, leaf lifespan, leaf area, phenological variability, polycyclic growth, shoot elongation. ecologia mediterranea, tome 29, fascicule 1, 2003, p. 15-25 Résumé Pendant deux ans, la phénologie et la croissance du chêne vert (Quercus ilex L.) ont été étudiées dans quatre localités de Sicile, dans le but de contribuer à la connaissance de l’écologie et de la plasticité adaptative de cette espèce. Les aspects suivants ont été considérés : le débourrement, la floraison, la fructification, la croissance des pousses, le turn-over des feuilles, et la surface foliaire. Les résultats ont montré une certaine variabilité des réponses parmi les quatre populations étudiées. Une précocité pour la plupart des phases phénologiques, un taux de croissance plus marqué et une croissance polycyclique ont été observés seulement au Mt. Pellegrino, site le plus “océanique” et le plus chaud parmi ceux étudiés. En outre, ces caractères sont vraisemblablement encore plus prononcés en raison d’autres particularités climatiques de ce site, telles que l’humidité atmosphérique très élevée et les automnes doux. D’après nos résultats, le chêne vert montre une capacité adaptative notable face à des environnements très différents. La réponse du chêne vert dans la population du Mt. Pellegrino est assez cohérente avec l’hypothèse d’une origine de l’espèce au sein d’un climat de type tropical. Mots-clés Ecophysiologie, turn-over foliaire, surface foliaire, variabilité phénologique, variability, croissance polycyclique, croissance des pousses. 15
16 u T. LA MANTIA, S.CULLOTTA & G. GARFÌ INTRODUCTION The adaptation of plants to different microclimatic conditions is expressed by their phenologyical behaviour that controls shoot growth, flowering, fruiting, leafing, leaf shedding (Chabot & Hicks, 1982; Kikuzawa, 1989). Hence, the study of these features may be an important key to understand the response of plant species to different environmental conditions (Leith, 1974; Kikuzawa, 1995). Within the sclerophyllous plant communities widespread in the western Mediterranean Basin, holm oak (Quercus ilex L.) plays a major role in the vegetation structure and species diversity (e.g. Barbero et al., 1992; Romane & Terradas, 1992; Rodà et al., 1997). The ecological optimum of holm oak lies in the plant communities referred to the Quercetalia ilicis, but it often penetrates in the broad-leaved forests (Querco-Fagetea) at the upper limits, and in the sclerophyllous matorrals (Pistacio- Rhamnetalia) at the lower ones (Barbero et al., 1992; Pasta et al., 2000; La Mantia et al., 2000). Environmental conditions are very unpredictable in Mediterranean-type ecosystems, especially due to water availability that limit functional activities in individual species, populations or communities (Mooney & Dunn, 1970; Aschmann, 1973). Several aspects of the ecology of holm oak show that this species is well adapted to the Mediterranean climate. A close relationship has been pointed out between the present climatic conditions and phenological and growth features (Gratani et al., 1989; Gratani & Crescente, 1997). However, some physiological aspects, especially concerning reproduction, suggest a tropical atavism (Bernetti, 1995). In fact, holm oak spread in the Mediterranean Region when a tropical-type climate dominated in that area. Indeed, according to some studies, its adaptation to the typical Mediterranean climate can be related to a xero-resistence strategy, rather than to a true xerophilism (Gambi, 1986). It is likely that this species can show different adaptive behaviours to various microclimatic conditions (Crescente et al., 2002), depending on genetic variability that in Sicily seems to be very high (Michaud et al., 1992; La Mantia, 1999). In the present paper, some phenological aspects of Quercus ilex were investigated in four different sites in Sicily. The aim was at contributing to the knowledge of the adaptive plasticity of this species to different environmental conditions through its phenological responses, in terms of flowering timing, leaf lifespan and seasonal leaf area variation. MATERIALS AND METHODS Study sites The investigated sites, namely Mt Pellegrino (Palermo), Mt Carcaci (Sicani Mts), Piano Zucchi (Madonie Mts) and Mt Maletto (Etna), lie in four different mountain massifs, respectively located from West to East, in the northern part of Sicily (fig. 1). Table 1 reports the main geographic and environmental features of the four study sites. The stands are usually located above 1 100 m a.s.l., except Mt Pellegrino which is about 115 m a.s.l. and is the closest one to the seaside. Climate is typically Mediterranean; following the site, precipitation ranges from about 600 mm to over 1 000 mm/year and mean annual temperature never drops below 9 °C not raises above 19 °C (Regione Siciliana, 1998). According to Rivaz-Martinez (1991), bioclimate is thermo- Mediterranean to supra-Mediterranean. Any-way, it must be added that at Mt Pellegrino, the humid sea streams notably contribute to the total water availability. Geological substratum varies from limestones to volcanites, whereas lithosols and rock outcrop are rather frequent in the soils of all sites. Vegetation is usually dominated by Quercus ilex, which is associated with different species, according to altitudinal vegetation belts (Cullotta, 2003). In coastal and basal belts, characterized by a thermo-Mediterranean bioclimate, the dominant physiognomy type is the maquis, mainly composed by the following woody species: Quercus coccifera, Quercus pubescens, Quercus suber, Pistacia lentiscus, Olea europaea subsp. europaea, Erica arborea, Pyrus amygdaliformis, Fraxinus ornus, Spartium junceum, Prunus spp., etc. Lauriphilous elements, such as Viburnum tinus, are also found at Mt Pellegrino. In more mesophilic conditions with a meso-Mediterranean bioclimate, in submountain and mountain belt, Quercus ilex constitutes forest stands mixed with Quercus pubescens, Quercus cerris, Acer campestre, Sorbus torminalis, Fraxinus ornus, Castanea sativa, Pyrus amygdaliformis, Crataegus monogyna, Rubus ssp. and Prunus spp. All stands are currently represented by aged coppices that until few decades ago were regularly exploited for fuelwood and charcoal production. In each study site, a sample area about 5000 m2 large was chosen and phenological observations were recorded from February 1988 to October 1999 in three selected trees per area. ecologia mediterranea, tome 29, fascicule 1, 2003
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