Plant Polsters and Pollen
Oh No, You Mean Even Plants Are Becoming Involved in Politics?
By: H. Wayne Shew, Ph.D.
NAB Certified Pollen Counter
We hear lots about political polls during election cycles and we are periodically treated to the lasted Gallup poll about the public’s opinion on some issue in the news. You may even have polls conducted occasionally where you work in order to determine preferences for items, or popularity of events in your workplace. Perhaps you are not aware that just as you have Gallup and Pew and other pollsters for humans, there are also plant polsters that can tell you something about the types and numbers of plants in a given area by identifying and counting the pollen grains present on the plant polsters.
A tremendous amount of pollen is produced annually by seed-producing plants, the gymnosperms and angiosperms. For example, estimates of the mass of pollen produced by almond trees varies between five to eight pounds per acre. Almond flowers are insect pollinated (entomophilous) and hence they produce less pollen than that produced by wind pollinated (anemophilous) flowers such as those produced by ragweed or pines or oaks. The estimated mass of pollen produced in a fully-grown forest of pine trees is between 35 to 55 pounds per acre. Where does all of this pollen go?
Only a small fraction of the mass of pollen produced by plants is involved in pollination of flowers and subsequent fertilization of ovules in flowers, steps necessary for the production of seeds. Most of the pollen produced by plants ends up in water or on the ground. For insect pollinated plants some of the pollen ends up in the hives of bees, while much of it is deposited on the ground or body of water very near where the plants are growing that produced it. Much of the pollen that falls into nearby bodies of water will be consumed by various invertebrates and microorganisms. For example, the pollen grains landing in water may be consumed by fungi (a division of fungi called the Chytridiomycota have numerous members that feed on pollen grains and I will talk about this group of fungi in a future blog). The pollen grains may also be eaten by other microorganisms and bacteria; but most will settle to the bottom of the body of water and become covered with silt and mud. Since the wall of pollen grains contains the highly resistant substance sporopollenin they are not readily decomposed. This means that pollen grains trapped in sediments can be used to identify species of plants present in an area in the past, as well as provide an estimate of the size of the populations of various species in an area during the past. “Sporopollenin is one of the most chemically inert biological polymers. It is a major component of the tough outer (exine) walls of plant spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments. The exine layer is often intricately sculptured in species-specific patterns, allowing material recovered from (for example) lake sediments to provide useful information to palynologists about plant and fungal populations in the past. Sporopollenin has found uses in the field of paleoclimatology as well.” —From definition of sporopollenin found in Wikipedia.
The pollen grains that land on the ground may be eaten by invertebrates and microorganisms, but much of the pollen remains undigested for various periods of time due to the highly resistant sporopollenin present in the exine of the pollen grains. Some of the pollen lands on moss or other types of plant polsters and may accumulate over time, (see images below). Moss polsters are defined as clumps of moss plants or cushions of moss plants that trap soil, pollen, debris, etc. Note: In case you are not familiar with the plants called mosses, they are defined as those leafy-stemmed, flowerless plants that belong to the Class Musci. Mosses reproduce by spores, not seeds. They often grow as mats or tufts on moist soil, tree trunks, rocks, etc.
Moss polsters can be used much like lake sediments to determine the types of plants present in a particular area by examining the pollen grains that get trapped on the moss plants over time. Since most of the pollen present on such polsters will be from nearby plants, the moss polsters not only provide information on the types of plants in the area, but also serve to give some idea of the population size of these species of plants in the recent past.
Pollen is found everywhere around us but we usually don’t think about it being so prevalent because it is not readily visible. (The exception to this statement of course is during the spring of the year when the pine and oak pollen is produced in such large quantities in the Southeastern U.S. that it collects on objects outside and coats them with a yellow to yellow-green “dust.”) Pollen is resistant to decay and has proven to be useful to palynologists and ecologists in the study of ecosystems both past and present. The next time you hear the word pollster don’t just think about Gallup or Pew or political, rather, consider that plants such as mosses can be used to tell you something; that is, botanical polling data. This polling is not about politics or preferences for television viewing, but about populations and types of plants in a geographical area.