As a general rule, the wind-pollinated plants produce and disperse millions of pollen grains in the hope that a few of them will be carried to their intended destination by the winds. As a result, in any given location there may be thousands or even millions of pollen grains falling to the earth’s surface in what is called a region’s ‘pollen rain’. This is why the most frequent pollen types recovered in sediment and soil samples are from wind-dispersed plants. The insect-pollinated plants, which are sometimes pollinated by bats, humming birds, small mammals, or a host of insect species, usually produce flowers containing nectar and relatively few pollen grains. Normally, these plants need to produce only a few hundred or a few thousand pollen grains per flower because of the highly efficient method of direct pollination achieved by the various pollen carriers that visit the flowers. The pollen grain surface of most insect-pollinated types is usually covered with lipids so they will stick easily to insects that visit the flowers. In addition, these insect-pollinated plants usually produce highly ornamented pollen grains with thick, sturdy pollen walls designed to protect the pollen’s cytoplasm from the often bumpy ride provided by the pollinators. In general, insect-pollinated pollen types are also heavy and overall are not designed aerodynamically for travel on wind currents. For all of these reasons, few of these types become part of the normal pollen rain of a region. One exception would be instances where flowers still containing a few pollen grains might fall to the surface underneath the parent plant, thus allowing the pollen to become released as the flowers decay. Another exception would be situations where insect-pollinated flowers are carried to a specific location by some animal or human.
Using several lines of logic and planned sampling strategies, pollen in burial soils that results from cultural activities, called ‘economic pollen’, can be separated successfully from pollen that may have come from the normal pollen rain, referred to as ‘background pollen’. First, if one of the pollen types in the soils of a burial matches an ethnographic or archaeological food plant species endemic to the region, or comes from a plant that may have been obtained in trade, then that pollen should be considered as potentially reflecting the use of that plant as a food source. However, roots, tubers, corms, and other underground plant organs will not carry attached Pollen with them from the source plant, so there is reduced potential for the pollen from these types to be represented in the site. Seeds and fruits from some plant species that are brought to a site often do carry pollen on their outer surfaces and thus such pollen types can reflect plant usage. Nevertheless, even with such types of potential pollen sources, one must be careful to distinguish pollen evidence suggesting actual plant usage and pollen that may be from background sources. For example, a number of types of economic chenopods, including Chenopodium qui-noa, and amaranths (Amaranthus) produce pollen that is nearly identical to the pollen of many noneconomic genera and species in these same plant groups. Trying to distinguish which pollen types are from economic plants rather than from noneconomic background types is often nearly impossible to determine without extensive studies using the resolution capability of a scanning electron microscope.
Pollen concentration values add another dimension to pollen data from burials and coprolites. For example, 10 maize pollen grains out of each 100 pollen grains recovered from a soil sample would be recorded as a 10% average. Similarly, 10 000 maize pollen grains out of 100 000 would also be recorded as a 10% average. However, there is a significant difference in terms of the potential importance and source of maize pollen in each of those two samples. That difference can only be realized by conducting pollen concentration values of both samples.
Low concentrations of some pollen taxa in copro-lites or soil deposits may result from sources of ambient pollen in the normal pollen rain (pollen distribution in a region). However, high concentration values of the same pollen taxa would suggest some type of disturbance or cultural activity rather than resulting solely from normal pollen rain distributions. Knowing the types of percentages of pollen found in burial sediments and coprolites in burials is important because the relative pollen percentages may be roughly the same in both types of samples; however, there may be dramatically differences in the pollen concentration values. This is illustrated in the Mimbres burial (Table 1) examined by Shafer et al. For example, maize pollen percentages are not statistically different between the control sample and samples from the sacral coprolites. However, the maize pollen concentration values reveal an average concentration of only 266 pollen grains per gram for the control sample but 59 280 pollen grains per gram for the sacral coprolite sample.
The above discussion briefly describes some of the factors that should be considered during the analysis and interpretation of pollen materials collected from burials at archaeological sites. In addition to these, there are other, even more important considerations that must be applied to pollen studies of burial deposits. These include (1) the assurance that the person conducting the pollen analysis has not accidentally contaminated the field samples with other pollen types in the laboratory that come from the use of unclean laboratory equipment or facilities; (2) the knowledge that the researcher has not accidentally
Lost or destroyed potential pollen in a sample by using incorrect or harsh extraction procedures; (3) that the person has a working knowledge of the pollen flora of the region where he or she is conducting the analysis; and (4) that all identifications of pollen types are accurate and are based on comparisons with modern reference materials of known pollen taxa.
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