The naturalization of the almond Prunus dulcis in different ecological contexts in the Mediterranean: An underestimated process?

Although Prunus dulcis has been frequently listed in non-native floras all around the world, its naturalization has been rarely studied in the field. Probably, because this species has generally invaded synanthropic habitats. We assessed the density of natural regeneration of almond, biometric parameters (height and basal stem diameter), and the distribution in life stage classes in three different ecological contexts in Sicily (Mediterranean Italy): one natural habitat (maquis), one pine afforestation and two prickly pear orchards. We recorded 236 naturally regenerating almond individuals, with density ranging from 140 individuals per hectare (prickly pear orchard 1) up to 2,400 individuals per hectare (pine afforestation). Despite the higher density, almond individuals presented the lowest height and basal stem diameter under pine afforestation, suggesting a more recent establishment. Reproductive individuals were dominant (67.8%), followed by pre-reproductive (22.1%), and juveniles (10.1%). Although the naturalization of the almond in Mediterranean contexts is not new, in the last two decades there is evidence of an increasing trend. Most importantly, for the first time, we found the almond thriving within a natural habitat in large areas covered by Mediterranean maquis. Since the almond appears to be perfectly integrated within local plant communities, the origin and meaning of this peculiar vegetation aspect deserve to be further deepened.