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In this article we will discuss about the pollen and spore production and dispersion, pollen sinking speed, pollen degradation, and pollen recycling are important consideration in the study of forensic palynology.
1. Pollen and spore production and dispersion:
If one know what the expected production and dispersal patterns of spores and pollen along with their flowering calendar of the plants in a given area, then one will know what type of pollen ” fingerprint ” to expect in samples that come from that area.
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Therefore, the first task of the forensic palynologists is to try to find out a match between pollen in a known geographical region with the pollen in the forensic sample. Knowledge of pollen productivity and dispersion play a major role in solving such problems.
There are a number of different methods by which plants disperse their pollen and spores. Many flowering angiosperms that live completely submerged in water release their pollen underwater, relying on water currents to transport the pollen from the male anther to the female stigma of a neighbouring flower.
Since, these plants produce pollen types that consist only a single layered cellulose wall, the pollen is almost never preserved in lake .sediments and generally oxidized rapidly if removed from water. Thus because of these limitations, these types of pollen are of little potential value for forensic work.
Pollens from autogamous group of plants produce less than 100 pollen grain per anther. Pollen from these plants is rarely dispersed into the atmosphere even though their pollen preserves well and has durable outer walls. Thus their minimal number in most regions carries little forensic value. Pollen from zoogamous plants generally have a thick exine that offers essential protection from humidity changes and possible abrasion during transport.
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The potential value of this pollen in forensic work is excellent for two reasons:
1. They have some of the most durable exines, thus will remain preserved in deposits for long period of time;
2. This pollen is produced in low amounts and thus normally not a potential contaminant in the pollen rain of the area. This last point is both good and bad. It is good because if the pollen of a given species of zoogamous plant is found in a forensic sample , there is a high degree of confidence that the pollen belongs with the sample and is not an atmospheric contaminant. It is bad because so little pollen is produced by each zoogamous plant that the chances of its pollen getting into any sample are reduced.
The anemophilous plants include the mosses, ferns, gymnosperms, and angiosperms. They produce high volume of spores or pollen (each anther containing 10,000 and 1, 00, 000 pollen grains, e.g., Eucalyptus, Pine, Oaks, Birch, Alder, Elm, Grasses, Ragweed, etc.) and thus are most common in the pollen rain of a region. As such, anemophilous types are the most common in the fossil pollen/spore record of a region are also the most common types analyzed for forensic studies.
2. Pollen sinking speed:
This factor determines that how much pollen actually becomes part of the pollen rain or the rate at which a pollen grain falls to earth. The pollen of Marijuana, Birch, Juniper, Alder, Eucalyptus, etc., is very small and light. Their average fall rate is about 2cm per second.
On the other hand Maize and Fir produce pollen that are large and heavy and have a rate of fall fifteen times faster than the lighter ones. Thus just using these two examples one can see that the potential distribution area of Maize and Fir pollen grains will much smaller and more restricted than the dispersion area covered by the plants in the first category.
From the forensic point of study, it means that when Maize and similar types of large and heavy pollen grains are found in samples, then small dispersion areas are indicated and greater precision in identifying the source region may be possible.
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3. Pollen degradation:
It is important that while examining forensic samples, paleontologists must consider how much, and which types of pollen maybe missing due to differential preservation and degradation. It has been noted from the studies of many scientists that all pollen types do not preserve equally well in sediments.
Pollen grain from grasses, Compositae and Pine are very durable and remain preserved long after other pollen grains have oxidized or become so degraded that they are no longer recognizable. However, pollen samples studied are very often from modern deposits, thus the problem of degradation or differential preservation no longer exits.
4. Pollen recycling:
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It is yet another problem that must be considered while examining forensic samples. Frequently pollen eroding from earlier deposits can become incorporated into contemporary samples. In certain cases recycled pollen can provide valuable information about specific locality and can be used to pinpoint regions precisely.
If recycled pollen grains cannot be distinguished from the normal pollen rain, the addition of recycled pollen may mask the true identity of target locality. This could occur when the combined pollen assemblage (modern+ recycled) suggests a flora quite different from floral reconstruction based on modern pollen control samples collected from the same location.
