The work of piecing together this chronology of events has been long and tedious. Pollen grains have two very important attributes. First they are very resistant to decay, especially is places where there is little or no oxygen. Such places are bogs and lake bottoms. Second each plant genus, and frequently each species, has pollen that has distinct characteristics that allow it to be identified positively.
Pollen is shed each time that a plant flowers and much of it falls to earth.
Where ever it falls in oxygen poor areas such as bogs and lakes it becomes incorporated into the peat or the sediment. This is a process that provides ages as far back as 50,000 years, often to within a few hundred years. Thus by dating a layer of peat or sediment and then analyzing the pollen it is possible to reconstruct the vegetation of that particular region at a particular time. The present day flora of the Great Lakes Region and Western New York State is dependent upon several environmental factors. The moderating effects of Lake Erie and Lake Ontario, and to a lesser extent the St Lawrence River means that the climate is not as severe as would be dictated by latitude alone.