Cannabis pollen sources and dispersal in the Iberian Pyrenees during the last century: Preliminary results and proposals for future studies

Meta-analyses of past pollen records have provided insights into the historical biogeography of Cannabis across the Iberian Peninsula (IP), with the southern Pyrenean flank being key to understanding cannabis cultivation and use during the Middle and Modern ages. However, studies on more recent times are rare. This paper offers a high-resolution comparison of the last century, particularly the significant Cannabis pollen peak observed in the mid-elevation Lake Montcortès between 1980 and 2000 CE, which was absent in the nearby highland Lake Sant Maurici. The Montcortès peak is linked to a phase of extensive hemp cultivation (1972–2006 CE) in the southeastern lowlands. The absence of a similar peak in Sant Maurici, despite the presence of other lowland pollen taxa, notably Olea and Quercus, suggests regional differences in pollen origin and dispersal likely influenced by wind patterns and rainfall. Studies on Cannabis pollen sources and dispersal are comparatively scarce and insufficient to provide a regional picture across the IP, similar to Olea or Quercus. However, the available data suggest that cannabis pollen is abundant mostly locally, in the vicinity of cannabis crops. The persistent presence of Cannabis pollen in Montcortès after 2000 CE likely reflects ongoing illegal cultivation. The study recommends combining paleoecological and aerobiological surveys to better understand pollen dynamics in the Iberian Pyrenees, with suggestions for future research based on these findings.