The Midwestern, USA Ambrosia Rise

Ambrosia is an important weed, especially in the Midwest, but also farther
east. The "Ambrosia-rise" is indicative of European settlement throughout
this region. Ambrosia becomes established on disturbed ground, especially
plowed areas. Small-grain farming (as opposed to corn and beans) is
especially favorable for Ambrosia, because it reaches maturity and flowers
in late summer, tyically after small grains are harvested. In Midwestern
sites we often see a decline in Ambrosia post-WWII with the decrease in
small-grain acerage and the increase in corn and beans, which are harvested
later. Herbicides probably also played a role. Ambrosia is still plenty
abundant in the Midwest, however.

Ambrosia is abundant in areas that were cleared of forest and then
converted to agricultural lands, but not particularly after logging or fires.

Today, Ambrosia is not the most important weed in the Great Plains, at
least north of the Sandhills. Chenopods, especially the introduced Salsola
and Kochia, are the important weeds in the drier Great Plains, and the
Salsola-rise is the important indicator of European settlement. However, in
the mid-Holocene, Ambrosia was extremely abundant in the Dakotas, and
farther east as well. Ambrosia percentages fluctuated greatly in the
mid-Holocene, and we have evidence that high Ambrosia is indicative of
droughts. Studies by Weaver during the 1930's drought support this

Eric Grimm

References from Eric Grimm 5/18/00 Weaver, J.E. 1954. North American Prairie. Johnsen Publishing Company, Lincoln, Nebraska. Weaver, J.E., and T.J. Fitzpatrick. 1934. The prairie. Ecological Monographs 4:109-295. [This has been reprinted as a book. The work was done before the drought so provided the very fortunate baseline data.] Weaver, J.E., L.A. Stoddart, and W. Noll. 1935. Response of the prairie to the great drought of 1934. Ecology 16:612-629. Weaver, J.E., and F.W. Albertson. 1936. Effects of the great drought on the prairies of Iowa, Nebraska, and Kansas. Ecology 17:567-639. Weaver, J.E., and F.W. Albertson. 1943. Resurvey of grasses, forbs, and underground plant parts at the end of the great drought. Ecological Monographs 13:63-117. Albertson, F.W., and J.E. Weaver. 1944. Nature and degree of recovery of grassland from the great drought of 1933 to 1940. Ecological Monographs 14:391-479. Weaver, J.E., and I.M. Mueller. 1942. Role of seedlings in revovery of midwestern ranges from drought. Ecology 23:275-294. Albertson, F.W. 1965. Vegetation changes during a 30-yr period in grassland communities near Hays, Kansas. Ecology 46:714-720.

To add to Eric Grimm's reply, Ambrosia is abundant in the middle to late-middle Holocene of much of the central Midwest. Three species are in the area today and all were probably represented in the fossil record to some degree. A. trifida, giant ragweed, grows in midwestern prairies, especially along waterways, usually where there is some disturbance. Its fruits are distinctive, and it is definitely widespread in the fossil record. A. artemisiifolia, common ragweed, also grows in disturbed areas, but it is common even on small disturbances like gopher mounds in native prairies, at least in Iowa. These first two species are native annual weeds. A. psilostachya is a perennial ragweed that is found to some degree in native undisturbed prairies. It is difficult (impossible?) to distinguish these latter two as fossils, but one or both are also widespread. 3/30/00 Dick Baker

The initial reference may be:

Ogden, J.G. III 1966.
Forest history of Ohio. I. Radiocarbon dates and pollen stratigraphy of Silver Lake, Logan County, Ohio. Ohio J Sci 66: 387-
(Cited in)
Wright, H.E.Jr. 1971.
Late Quaternary Vegetational History of North America. Pp. 425-464 IN: K.K. Turekian (ed.) The Late Cenozoic Glacial Ages. Yale Univ Press.

this was followed by McAndrews' and Waddington's papers. etc.

Baker, R.G., Schwert, D.P., Bettis, E.A.III, Chumbley, C.A. 1993.
Impact of Euro-American settlement on a riparian landscape in northwest Iowa, Midwestern USA: an integrated approach based on historical evidence, floodplain sediments, fossil pollen, plant macrofossils and insects. Holocene 3: 314-323.

Bradbury, J.P. and Waddington, J.C.B. 1973.
The impact of European settlement on Shagawa Lake, northeastern Minnesota, U.S.A. pp. 289-308 IN: Birks, J.H.B. and West, R.G. (Eds) Quaternary Plant Ecology. John Wiley and Sons, NY.

Brugham, R.B. 1978.
Pollen indicators of land-use change in southern Connecticut. Quaternary Research 9:349-362.

Grimm, E.C. 1983.
Chronology and dynamics of vegetation change in the prairie-woodland region of southern Minnesota, U.S.A. New Phytologist 93: 311-350.

McAndrews, J.H. 1968.
Pollen evidence for the prehistoric development of the “Big Woods” in Minnesota, U.S.A. Review Palaeobotany Palynology 7: 201-211.

McAndrews, J.H. 1988.
Human disturbance of North American forests and grasslands: The fossil pollen record. Pp. 673-697 IN: Huntly, B & Webb, T. III (eds.) Vegetation History. Kluwer Academic.

McAndrews, J.H. and Boyko-Diakonow, M.. 1987.
Pollen analysis of varved sediment at Crawford Lake, Ontario: evidence of Indian and European farming. IN: Fulton, R.J. and Heiginbottom,. J.A. (eds.) Quaternary geology of Canada and Greenland. Geol. Surv. Canada.

Strong, W.L. 1977.
Pre- and postsettlement palynology of southern Alberta. Review Palaeobotany Palynology 23: 383-396.

Van Zant, K. 1979.
Late-glacial and postglacial pollen and plant macrofossils from Lake West Okoboji, Northwestern Iowa. Quaternary Research 12: 358-380.

Waddington, J.C.B. 1969.
A stratigraphic record of pollen influx to a like in the Big Woods of Minnesota. Geol. Soc. Amer. Special Pap. 124: 263-282.

Webb, T. III 1973.
A comparison of modern and presettlement pollen from southern Michigan (U.S.A.). Review Palaeobotany Palynology 16: 137-156.