Cannabis Pollen Sources and Dispersal in the Iberian Pyrenees: Hemp Cultivation vs. Illegal Drug Farming

16 Pages Posted: 1 May 2024

See all articles by Valentí Rull

Valentí Rull

Spanish National Research Council (CSIC)

Javier Sigró

Rovira i Virgili University

Teresa E. Vegas-Vilarrúbia

University of Barcelona


Meta-analyses using pollen databases have provided a regional picture of the Cannabis historical biogeography across the Iberian Peninsula (IP) since prehistoric times. The southern Pyrenean flank has been crucial to understand the patterns of cannabis cultivation and use during the Middle and Modern ages, when these practices flourished, but studies on more recent times are virtually non-existent. This paper presents a comparative high-resolution study of the last century in the sediments of two Pyrenean lakes focused on the last decades, when a major Cannabis pollen peak (20C) occurred between approximately 1980 and 2000 in the mid-elevation Lake Montcortès, but was absent in the highland Lake Sant Maurici. The Cannabis pollen peak was attributed to a transitory phase (1972-2006) of extensive hemp cultivation (EHC) in the southeastern lowlands. The lack of a similar peak in Sant Maurici sediments – together with the presence of pollen from lowland taxa (Olea, Quercus) in significant amounts – was addressed in terms of source location and dispersal patterns. Olea and Quercus are widespread and abundant across the IP and their pollen disperses regionally in significant amounts. However, Cannabis is restricted to small crops and its pollen is abundant only locally. In addition, the predominant winds around Montcortès are from the east-southeast, where the EHC region was located, whereas in Sant Maurici the dominant winds flow from the opposite direction. Additionally, Montcortès is situated in a rainy area where heavy rainfall events may enhance the washout of atmospheric pollen thus preventing its further dispersal to highlands. After the 20C peak, cannabis pollen in Montcortès sediments did not disappear, likely due to the continuity of cannabis cultivation, this time in the form of illegal drug plantations. The combined use of paleoecological and aerobiological surveys is encouraged to enhance understanding of cannabis pollen dynamics.

Keywords: Cannabis, Pollen, hemp, marihuana, dispersal, Iberian Peninsula

Suggested Citation

Rull, Valentí and Sigró, Javier and Vegas-Vilarrúbia, Teresa E., Cannabis Pollen Sources and Dispersal in the Iberian Pyrenees: Hemp Cultivation vs. Illegal Drug Farming. Available at SSRN: or

Valentí Rull (Contact Author)

Spanish National Research Council (CSIC) ( email )

Javier Sigró

Rovira i Virgili University ( email )

Av. Universitat 1
Tarragona, 43204

Teresa E. Vegas-Vilarrúbia

University of Barcelona ( email )

Gran Via de les Corts Catalanes, 585
Barcelona, 08007

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