Increased Cannabis/Humulus pollen, an indicator of European agriculture in Iowa

Abstract

The percentages of Ambrosia‐type pollen increase in the upper few centimeters of many North American cores of lake sediments or bog peats, For much of eastern North America south of 50 °N, this increase is easily recognizable in pollen diagrams and indicates the time when persons of European origin settled in an area. The actual biostratigraphic proof that this "Ambrosia rise”; occurs with settlement requires correlating the Ambrosia rise with the first appearance or the rise in abundance of pollen types from both cultivated and non‐native plants. This requirement is particularly important in the Midwest where Ambrosia is a native weed. Our results illustrate the potential of Cannabis/Humulus pollen as an indicator of settlement and cultivation in Iowa.

Pollen of Cannabis/Humulus increases in abundance at or just after the initial rise in Ambrosia‐type pollen in sediments from two Iowa lakes. It first occurs in the sediments of Lake West Okoboji at ca. 1910 AD, which is after the initial Ambrosia‐type pollen rise but approximately dates when Cannabis sativa was introduced into the state for cultivation for fiber. A similar rise in Cannabis/Humulus pollen at Blackhawk Lake is correlative with the Ambrosia rise. Cultivation of Cannabis sativa for fiber ceased in Iowa in 1940, but the plant has escaped from cultivation and now grows in waste places.