PALYNOLOGY

The growth patterns of trees reflect the climate of the region. Tree growth is an important climate indicator, but tree reproduction is revealed through arboreal pollen counts.  The advantage of palynology is that all plants need to reproduce and consequently leave their pollen behind.  This pollen is uniquely identifiable to the genus and sometimes species.  These pollen counts have become the basis for many paleoclimatological studies (Birks and Birks, 1980) .

Pollen collected from lake and bog sediments is used to develop climatological interpretations.  Certain plants can give better insight into past climates than others, due to their sensitivity to climatic change.  The generalizations revealed by the types and relative abundances of flora that are surviving shed light upon the climate at the time.  Identifying species and quantifying species’ abundance within a plant community in a particular area can also reveal information about the temperatures and precipitation amounts that generally maintain a particular community (Lamb, 1977) .

There are several assumptions that have to be made to yield a successful pollen-based climate reconstruction.  There has to be a belief that the climate does not differ from meteorological data, such as temperature, wind, and precipitation.  There needs to be an understanding that plant species respond differently in different ecosystems.  Further, some agricultural responses may be initiated through competition among other species of the same area, not solely dependent upon climate variations.  Climate changes may also only affect immature plants but leave the adult plant unimpacted.  Edaphic characteristics, topography, and even the intervention of animals, including humans, also can contribute to a change in pollen counts.  Most importantly, one has to accept that there can never be a perfect equilibrium between plant and climate outside of theory (Birks and Gordon, 1985) .

            Through the sampling of radiocarbon-dated pollen sequences and reconstruction of plant assemblages of the time, the climate can be assigned a set of climatic boundaries within which the plants are capable of surviving.  Unfortunately, the pollen-based chronology is far less accurate than tree-ring chronologies.  Only a few points in a pollen core are sampled and given accurate radiocarbon dates (which have associated error, even if calibrated), while the remainder of the core is interpolated between these samples and given approximate dates (Becker, 1993) .  The reason this procedure is followed is that radiocarbon dating is relatively expensive and sampling intensely down the core would be extremely costly.  Nevertheless, the interpolation helps clarify the climate under investigation, even if exact dating is impossible.  By knowing the climatic tolerances of the modern plant species and the general time that they existed, the limitation of the climate modeling is understood.

            Another advantage of palynology is the identification of peat growth.  Peat extent expands in wet periods, remains constant in average moisture regimes, and contracts in dry periods.  Peat competes with many trees and during very wet periods the rapid growth can eventually suffocate trees.  The fact that peat does not respond well to dry climates and usually dies is a good climatological indicator of the longer dry periods in history.  In turn, the abundance of peat and lack of arboreal pollen is a good indicator of a wet period (Moore et al., 1991, Faegri et al., 1989, Delcourt and Delcourt, 1985) .

            Furthermore, the types of pollen found in peat can help reconstruct the ecosystems of the time to which they were dated.  The general date of the pollen assemblage gives climatologists information about the flora and changes that occurred throughout the period.  This is supported by dendrochronological indices, which help support climatic inferences.

            Pollen is very resistant and exists for a very long time in the proper circumstances, thanks to their protein casings (Moore and Webb, 1978) .  This longevity of pollen allows palynology to identify, not only native plants that are good climate indicators, but agricultural crops as well.  Large quantities of agriculturally related pollen can be indicative of human habitation, but more importantly to this study is that it also potentially reveals what crops were being grown.  With the knowledge of the agricultural crops present, it is possible to identify their relationship to climate, as evident in tree rings.