Pollen and plant macrofossil data are the primary sources of information about past vegetation composition and pattern at timescales greater than 10² yr.  Pollen and plant macrofossil assemblages from lake and wetland sediments of humid regions are of critical importance in inferring past vegetation and environment, and have been studied from thousands of sites worldwide.  Studies of plant macrofossil assemblages from middens of woodrats (Neotoma spp.) in arid western North America have revolutionized our understanding of floristic, vegetational, and climatic changes of the past 40,000 years.

Accurate inferences from paleoecological data require understanding of the relationships between source vegetation and derivative fossil assemblage.  A long-term effort in the Quaternary Plant Ecology Laboratory at Universiy of Wyoming has been aimed at increasing our understanding of these relationships.  Our studies fall into four broad categories:
 

• Theory of pollen analysis: dispersal and calibration models

• Vegetation-sensing properties of pollen assemblages: empirical studies

• Vegetation-sensing properties of plant-macrofossil assemblages from lakes and wetlands

• Vegetation-sensing properties of plant-macrofossil assemblages from woodrat middens

The conceptual theory underlying Quaternary pollen analysis can be traced back to Lennart von Post's 1916 lecture on pollen in Swedish bog sediments.  However, formal theoretical treatment of pollen-vegetation relationships was largely neglected until the 1960s, when Margaret Davis proposed a model for pollen-vegetation calibration, and Henrik Tauber and M. Kabailiene applied atmospheric diffusion models to pollen dispersal.  Colin Prentice, together with R. Parsons, built on Davis' work to develop the Extended R-Value models (ERV), which take into account the non-linearities imposed by the "Fagerlind effect" in relating percentage variables.  Prentice also built on the work of Tauber and Kabailiene to develop a model relating pollen dispersal, basin size, and pollen-source area.  Shinya Sugita has developed a third ERV model and a landscape-based model for pollen-source area based on Prentice's model.

Our work has been aimed at clarifying and testing the assumptions and parameters of both the ERV models and the pollen-dispersal models.  We have also developed the FAGERLND program, which applies ERV models 1 and 2 to pollen-vegetation data sets.  We are compiling a pollen/vegetation calibration database for distribution; this database will include those developed in our empirical studies as well as some others from the literature.

The following papers present results of our work on theory of pollen analysis.  Our data papers on pollen representation in forest-floor sediments and small lakes also discuss some of these issues and test model predictions and assumptions.

• Jackson, S.T., & M.E. Lyford.  1999.  Pollen dispersal models in Quaternary plant ecology: assumptions, parameters, and prescriptions.  Botanical Review 65:39-75.
• Jackson, S.T., and J.B. Kearsley.  1998.  Quantitative representation of local forest composition in forest-floor pollen assemblages.  Journal of Ecology 86:474-490.
• Jackson, S.T., T. Webb III, I.C. Prentice, and J.E. Hansen.  1995.  Exploration and calibration of pollen/vegetation relationships: a PC program for the extended R-value models.  Review of Palaeobotany and Palynology 84:365-374.
•  Jackson, S.T.  1994.  Pollen and spores in Quaternary lake sediments as sensors of vegetation composition:  theoretical models and empirical evidence.  Pages 253-286 in Sedimentation of Organic Particles (A. Traverse, editor).  Cambridge University Press.

• Davis, M. B.  1963.  On the theory of pollen analysis.  American Journal of  Science 261: 897-912.
• Kabailiene, M. V.  1969.  On formation of pollen spectra and restoration of vegetation.  Transactions of the Institute of Geology (Vilnius) 11: 1-148.
• Parsons, R.W. and Prentice, I.C.  1981.  Statistical approaches to R-values and the pollen-vegetation relationship.  Review of Palaeobotany and Palynology 32:127-152.
• Parsons, R.W., Prentice, I.C., and Saarnisto, M.  1980.  Statistical studies on polen representation in Finnish lake sediments in relation to forest inventory data.  Annales Botanici Fennici 17:379-393.
• Prentice, I. C.  1985.  Pollen representation, source area, and basin size: toward a unified theory of pollen analysis.  Quaternary Research 23: 76-86.
• Prentice, I.C.  1986.  Forest-composition calibration of pollen data.  In:  B.E. Berglund (Editor), Handbook of Holocene Palaeoecology and Palaeohydrology.  John Wiley and Sons, Chichester, pp. 799-816.
• Prentice, I.C.  1988.  Records of vegetation in time and space:  the principles of pollen analysis.  In:  B. Huntley and T. Webb III (Editors), Vegetation History.  Kluwer, the Hague, pp. 17-42.
• Prentice, I.C. and Parsons, R. W.  1983.  Maximum likelihood linear calibration of pollen spectra in terms of forest composition.  Biometrics 39:1051-1057.
• Prentice, I.C. and Webb, T. III.  1986.  Pollen percentages, tree abundances and the Fagerlind effect.  Journal of Quaternary Science 1:35-43.
• Sugita, S.  1993.  A model of pollen source area for an entire lake surface.  Quaternary Research 39: 239-244.
• Sugita, S.  1994.  Pollen representation of vegetation in Quaternary sediments: theory and method in patchy vegetation.  Journal of  Ecology 82: 881-897.
• Tauber, H.  1965.  Differential pollen dispersion and the interpretation of pollen diagrams.  Danmarks Geologiske. Undersølgelse., Række 2, Number 89.

Since 1986 we have been conducting empirical studies of modern pollen assemblages and comparing the pollen data with vegetation composition data from local to landscape and regional scales.  The modern pollen assemblages are from forest-floor moss-polsters and from sediments of small lakes (<2 ha).    Our primary goals have been to determine more precisely the spatial scales at which vegetation patterns are represented in the assemblages, to test predictions and assumptions of pollen-representation and dispersal models, and to better understand the general vegetation-sensing properties of pollen assemblages.  Our results are concentrated in the following papers; additional papers are in preparation.
 

• Jackson, S.T., and J.B. Kearsley.  1998.  Quantitative representation of local forest composition in forest-floor pollen assemblages.  Journal of Ecology 86:474-490.
• Kearsley, J.B., and S.T. Jackson.  1997.  History of a Pinus strobus-dominated stand in northern New York.  Journal of Vegetation Science 8:425-436.
• Jackson, S.T., T. Webb III, I.C. Prentice, and J.E. Hansen.  1995.  Exploration and calibration of pollen/vegetation relationships: a PC program for the extended R-value models.  Review of Palaeobotany and Palynology 84:365-374.
• Jackson, S.T., and A. Wong.  1994.  Using forest patchiness to determine pollen source areas of closed-canopy pollen assemblages.  Journal of Ecology 82:89-99.
•  Jackson, S.T., and S.J. Smith.  1994.  Pollen dispersal and representation on an isolated, forested plateau.  New Phytologist 128:181-193.
• Jackson, S.T., and P.W. Dunwiddie.  1992.  Pollen dispersal and representation on an offshore island.  New Phytologist 122:187-202.
• Jackson, S.T.  1991.  Pollen representation of vegetational patterns along an elevational gradient.  Journal of Vegetation Science 2:613-624.
• Jackson, S.T.  1990.  Pollen source area and representation in small lakes of the northeastern United States.  Review of Palaeobotany and Palynology 63:53-76.
• Gaudreau, D.C., S.T. Jackson, and T. Webb III.  1989.  Spatial scale and sampling strategy in paleoecological studies of vegetation patterns in mountainous terrain.  Acta Botanica Neerlandica 38:369-390.

Plant macrofossil assemblages from sediments of lakes and wetlands are being used throughout the world to infer upland vegetation composition and past species ranges.  The vegetation-sensing properties of plant macrofossil data have received relatively litle attention compared to pollen data.  We have studies modern macrofossil assemblages from 25 small lakes in northern New York and New England, and are comparing the data to forest composition within 10, 20, and 100 m of the lake margins to assess macrofossil dispersal distances and taxon representation.  These analyses are nearing completion.  The following papers discuss aspects of macrofossil representation and application:
 

• Jackson, S.T., J.T. Overpeck, T. Webb III, S.E. Keattch, and K.H. Anderson.  1997.  Mapped plant macrofossil and pollen records of Late Quaternary vegetation change in eastern North America.  Quaternary Science Reviews 16:1-70.
• Jackson, S.T., and D.R. Whitehead.  1991. Holocene vegetation patterns in the Adirondack Mountains.  Ecology 72:641-653.
• Gaudreau, D.C., S.T. Jackson, and T. Webb III.  1989.  Spatial scale and sampling strategy in paleoecological studies of vegetation patterns in mountainous terrain.  Acta Botanica Neerlandica 38:369-390.
• Jackson, S.T.  1989.  Postglacial vegetational changes along an elevational gradient in the Adirondack Mountains (New York): a study of plant macrofossils. New York State Museum and Science Service Bulletin 465. 29 p.

Plant macrofossil assemblages from woodrat (Neotoma) middens are a key source of information on past flora and vegetation of arid and semiarid regions (see Betancourt et al., 1990).  However, the vegetation-sensing properties of midden assemblages have been little studied.  With what confidence can we infer absence of a particular species from the vicinity of a midden if that taxon is absent from the midden macrofossil assemblage?  Is the probability that a particular species is represented in a midden dependent on its population density in the vicinity of the midden?  We are conducting a comparative study of macrofossil assemblages from modern middens with vegetation composition and structure within 100 m of the middens.  The studies are being done in semiarid regions of Wyoming and adjacent Montana as part of the Utah-juniper invasion project.