Naturalization of almond trees (Prunus dulcis) in semi-arid regions of the Western Mediterranean.
Agricultural land abandonment is rampant in present day Europe. A major consequence of this phenomenon is the re-colonization of these areas by the original vegetation. However, some agricultural, exotic species are able to naturalize and colonize these abandoned lands. In this study we explore the ability of almonds (Prunus dulcis D.A. Webb.) to establish in abandoned croplands in semi-arid areas of SE Iberian Peninsula. Domesticated during the early Holocene in SW Asia and the Eastern Mediterranean, the almond has spread as a crop all over the world. We established three plots adjacent to almond orchards on land that was abandoned and reforested with Aleppo pine (Pinus halepensis Mill.) and Holm oak (Quercus ilex L.) about 20 years ago. We recorded the abundance of almond seeds, seedlings, juveniles, pre-reproductives and adults in these plots, and determined their recruitment microhabitat. We found natural regeneration in all three plots, with almond density higher than 150 individuals/ha in each plot. About half of the almonds in the plots were juveniles, although 7% were one-year seedlings and 3% were adult trees. This suggests that colonization of abandoned lands is an ongoing gradual process. Most naturally established almonds were under tree cover, although this was not the most abundant microhabitat, avoiding the negative impact of browsing by Red Deer (Cervus elaphus) and domestic sheep and goats. In addition, the mean distance from the nearest seed source was 77 m. These findings suggest the action of mobile almond dispersers. Several Corvid species including the Carrion Crow (Corvus corone) and the Magpie (Pica pica) have been observed consuming and moving almonds in the study area. Our study has demonstrated that almonds are colonizing abandoned lands mostly as a consequence of effective seed dispersal by some animals. We show that almonds have the potential to become fully naturalized in the near future in many semi-arid areas of the Western Mediterranean.