In response to the query on indicator weeds, here is a partial list
of references on the topic. There is also a lot of information
available through the phytosociology literature but it is often
in german or french.
Brooks, R.R. 1972. Geobotany and biochemistry in mineral exploration.
Harper and Row, New York. 290 pp.
Chaphekar, S.B. 1978. Biological indicators: the concept and new
additions. International Journal of Ecology and Environmental
Sciences. 4:45-52.
Chikishev, A.G. (Editor) 1965. Plant indicators of soils, rocks, and
subsurface waters. Consultants Bureau, New York. 210 pp.
(Translation of a Russian book).
Clements, F.E. 1920. Plant indicators: the relation of plant
communities to process and practice. Carnegie Inst. Wash. Publ.
No. 290. 388 pp.
Cocannouer, J.A. 1964. Weeds: guardians of the soil. Devon-Adair, New
York. 179 pp.
Dale, M.H. 1966. Weed complexes on abandoned pastures as indicators of
site characteristics. Canadian Journal of Botany 44:11-17.
Dale, M.H., P.J. Harrison, and G.W. Thomson. 1965. Weeds as indicators
of physical site characteristics in abandoned pastures. Canadian
Journal of Botany 43:1319-1327.
Duke, J.A. 1976. Perennial weeds as indicators of annual climatic
parameters. Agricultural Meteorology 16:295-298.
Hill, S.B. and J. Ramsey. 1997. Weeds as indicators of soil
conditions. Macdonald Journal June 1997, p.8-11, 16
Holzner, W. 1982. Weeds as indicators for the whole complex of
environmental factors. Geobotany 2:187-190.
Pfeiffer, E.E. 1970. Weeds and what they tell. Reoriented by
Biodynamic Farming and Gardening Association, Inc. P.O. Box 550,
Kimberton, PA 19442, USA.
Rogers, L.H., O.E. Gail and R.M. Barnette. 1939. The zinc content of
weeds of volunteer grasses and planted land covers. Soil Science
47:237-243.
Rorison, I.H. and D. Robinson. 1984. Calcium as an environmental
variable. Plant, Cell and Environment 7:381-390.
Shantz, H.L. 1911. Natural vegetation as an indicator of the
capabilities of land for crop production in the Great Plains area.
U.S.D.A. Bur. Pl. Ind. Bul. 201:1-100.