174 Bueno et al: Natural Regeneration of Persian Walnut in Mediterranean Agroecosystems Arboriculture & Urban Forestry 2020. 46(3):174–184 URBAN FORESTRY ARBORICULTURE Scientific Journal of the International Society of Arboriculture & First Assessment of Natural Regeneration and Seed Dispersal of Persian Walnut ( in Mediterranean Agroecosystems By Rafael da Silveira Bueno, Emilio Badalamenti, Ettore Barone, Andrea Cairone, Andrea La Mantia, Giovanna Sala, and Tommaso La Mantia Abstract. Persian walnut (Juglans regia L.), which is native to Central Asia, has been widely cultivated throughout Europe over millennia as a multipurpose tree. However, only recently the naturalization process outside cultivation has been studied, mostly in temperate Europe, with no information regarding the Mediterranean region. Here we provide the first field investigations about the natural regeneration of walnut in two traditional Mediterranean agroecosystems: an irrigated mixed orchard in suburban areas and a non-irrigated prickly pear (Opuntia ficus indica [L.] Mill.) orchard. The natural regeneration densities were statistically different in the two agroecosystems, ranging from 75 individu- als per hectare in the prickly pear orchard to 200 individuals per hectare in the mixed orchard. Crows were frequently observed actively carrying walnuts in both environments. The irrigation practices and the shade provided by larger trees in the mixed orchard, and the potential benefits provided by prickly pear individuals, seemed to be crucial for seedling establishment and development in the two orchards, respectively. On the other hand, climate does not seem to represent a constraint for walnut recruitment, even if the mean annual temperature at the mixed orchard is slightly above the optimal temperature for walnut. Other biotic and abiotic factors that may trigger or hamper the naturalization process are also discussed in this paper, which explores the research needs for better understanding the naturalization potential of the Persian walnut in Medi- terranean agroecosystems, as well as the effects of different land uses and future climate change on this process. Keywords. Agroforestry Systems; Climate Change; Corvus cornix; Naturalization; Walnut Recruitment. L.) INTRODUCTION One of the major issues facing the study of the inva- sion process by alien species is high unpredictability, either concerning which plant taxa will become inva- sive, or the time needed to reach an invasive status (Williamson 2006). This is also true for plant taxa which have been cultivated since ancient times and are seldom studied in their naturalization process (Verloove 2006). The duration of the lag-phases can be highly variable from species to species, so that plants that have never shown any tendency to natural- ization can suddenly spread even centuries after their introduction (Aikio et al. 2010). Several biotic and abiotic factors may trigger the naturalization process. For example, biotic interactions with the organisms necessary for pollination and seed dispersal, or the availability of water resources and nutrients, may be crucial (Glyphis et al. 1981; Badalamenti et al. 2014), ©2020 International Society of Arboriculture in addition to the relationships with primary biotic soil components, such as arbuscular mycorrhizal fungi (Badalamenti et al. 2015; Carvalho et al. 2018). The Persian walnut (Juglans regia L., Juglandaceae) is one of the most intensively cultivated nut tree spe- cies worldwide due to the high nutritional value of the fruits and good timber quality (Bottema 1980; Barone et al. 1997; de Rigo et al. 2016; Pelleri et al. 2020). Probably native to a large area of the mountain ranges of Central Asia, Persian walnut has been culti- vated for a long time throughout Europe, including the Mediterranean and temperate areas (Pini et al. 1999; Pollegioni et al. 2017). Walnut cultivation in Italy has very old traditions and probably dates back to the pre-Roman period (Barone et al. 1990). Origi- nally, trees for orchards were often produced from seed, a still-common practice in some Italian regions (Barone et al. 1997). Currently, walnut is propagated J ug lans r e gia
May 2020
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