Wild cherries invading natural grasslands: unraveling colonization history from population structure and spatial patterns

Invasive success of many fleshy-fruited plants has been linked to opportunistic interactions with generalist frugivores. Prunus mahaleb is a small tree, producing large quantities of little, bright black, sugary drupes that are consumed by vertebrates. It is native to the Mediterranean region but has become invasive in several countries. This study was carried out at a nature reserve including remnant mountain grasslands of high conservation value in the southern Argentine Pampas. Our aim is to reconstruct the colonization history of invading populations proposing a generalized model to describe the invasion process: colonization events result in the establishment of a founder tree followed by a lag phase until it reaches massive seed production and enables an increase in local recruitment and plant density. To test this hypothesis, we analyzed population age structures and contrasted them with those predicted using a Leslie matrix growth model. We found that matrix model predictions fit well to actual age structures. Our results reveal the existence of an 8-18-year lag period between the establishment of the founder tree and local effective recruitment. The end of this lag coincides with an abrupt increase in individual fruit production that may have a strong effect on bird attraction and successful seed dispersal. This lag phase represents an opportunity for preventing further spread of P. mahaleb. Early detection and rapid eradication of new invasion focuses should be targeted as a principal aim of an effective control strategy.