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Comparative pollen influx at a nine-trap array in the Grand Prairie of northern Texas.

ABSTRACT. -- An array of nine Tauber pollen traps at a tallgrass prairie site produced a mean annual influx of 9132 [+ or -] 956 (1 SD; 10.5 percent) grains per square centimeter per year. Ambrosia, Juniperus, and Quercus pollen dominated the spectra; Poaceae pollen averaged five percent. One-standard deviation for individual pollen taxa increased with lower mean influx values. Key words: pollen analysis; Tauber pollen trap; tallgrass prairie; southern Great Plains.

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Tauber traps have been used in the United States and Europe to characterize daily and annual pollen dispersal and deposition in alpine, forest, grassland, and desert vegetation (Tauber, 1977; Andersen, 1980; Markgraf, 1980; Solomon and Silkworth, 1986; Hall, 1990). The present study is the first attempt to determine the replicability of pollen influx from the Tauber trap (Tauber, 1974), using an array of nine Tauber trap stations established in a small protected area in a tall grass prairie of north-central Texas (Fig. 1).

METHODS

The nine traps were arranged in a small array, each trap about 20 feet (six meters) away from the next and about four feet (1.2 meters) above the ground surface on a low grassy hill in a fenced-from-grazing parcel of land within the tallgrass Grand Prairie, about four miles (6.4 kilometers) north of Denton, Denton Co., north-central Texas. The fenced trap site is surrounded by tallgrass rangeland and farm fields where varieties of maize and wheat are cultivated. The pre-European vegetation of the area was tallgrass prairie. Today, small trees grow along small steams and in some abandoned fields. The trap design in this study is the same as that used in the previously reported 320-kilometer transect on the southern Rocky Mountains and southwest High Plains (Hall, 1990). The top of the Tauber trap is affixed to a one-quart (1.1-liter) wide-mouth glass Mason jar by glueing the cast-in-plastic top to a threaded metal ring. The Tauber top is screwed onto the jar, which is placed inside a large metal can that is wired to a steel-T fence post. The lip of the Tauber-trap top protudes over the edge of the can and beyond the fence post. A metal wire mesh with openings of one-eight inch (0.3 centimeters) was placed below the aperature so as to keep large insects out of the collector jar. The initial diameter of the trap aperature was 5.00 centimeter; however, the curing process of casting results in a slight shrinkage; the aperature of each trap top was measured separately and taken into account when calculating pollen influx per square centimeter; in this study, trap aperatures diameters varied by 0.04 centimeters. The pollen content of the Tauber traps that accumulated in the array during the period from 5 February 1984 to 16 February 1985 is regarded in this analysis as one year of time.

In the laboratory, the contents of each jar were washed and scraped into a large beaker. A spike of eight Lycopodium spore tablets (11,267 [+ or -] 370 spores per tablet; batch 201890) was added to each sample. Each sample was treated overnight with hydrofluoric acid, washed eight minutes in hot acetolysis solution, and stained with safranin O. Two glycerin jelly slides were made of each sample. A strong effort was made to process the samples uniformly so as to minimize laboratory procedure as a variable in the analysis of the pollen content of the traps. During centrifuging, especially at the initial stage when concentrating the jar contents from the large beakers into 15-milliliter tubes for HF treatment, several drops of ethanol were splashed into the centrifuge tubes to break water surface tension, thereby allowing floating pollen grains to sink more readily during centrifuging. Although the jars were sealed and stored without preservatives for seven years before analysis, the condition of the pollen grains was excellent.

[FIGURE 1 OMITTED]

ANALYTICAL RESULTS

Pollen influx and percentage values for each trap were determined from the fixed count of 400 grains; the spike of 90,136 Lycopodium spores introduced into each sample resulted in about 200 spores tabulated in each sample (Table 1). The mean and one-standard deviation of total pollen influx for the nine traps is 9132 [+ or -] 956 (10.5 percent), excluding the statistical weight of both the 3.3 percent deviation of spore content in each of the eight Lycopodium tablets introduced as a spike and the confidence limits of the pollen counts and percentages. The pollen content of the traps was dominated by Ambrosia (equal to or less than 2.0 [micro]m), Juniperus, and Quercus, accounting for 61 percent of the pollen sum. Other taxa consistently present in each trap included, in descending importance, Cerealia (Zea and Triticum from adjacent cultivated fields), Poaceae, Franseria, Ulmus, Asteraceae (spines more than 2.0 [micro]m), Chenopodiaceae, Pinus, Carya, and Artemisia. Most of the taxa represented by pollen in the traps are local species, occurring within a mile radius of the array. Two taxa, however, Pinus and Artemisia, are extra-local (a few pines are planted as ornamentals in Denton, four miles south of the trap array) and comprise about two percent and one percent of the pollen sum, respectively. Cerealia pollen, averaging 630 grains per square centimeter per year and seven percent relative frequency, is included in the pollen sum. A plot of the mean and one standard deviation of individual pollen taxa from all nine traps shows that, in general, the lower the mean influx value, the higher its variability (Fig. 2). All of the influx values for individual taxa from each of the nine traps fall within two standard deviation (0.95 percent) of the mean of that taxon (Fig. 3). Confidence intervals (0.95 percent) of the pollen percentages from the traps were calculated with the formula discussed in Mosimann (1965) and used by Maher (1972). Confidence intervals on some percentages of Ambrosia, Juniperus, Quercus, Poaceae, Artemisia, and Asteraceae do not overlap; 0.95 intervals on all percentage values of Pinus, Carya, Ulmus, Franseria, and Chenopodiaceae are overlapping (Fig. 4).

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

[FIGURE 4 OMITTED]

DISCUSSION AND CONCLUSION

The pollen content of a Tauber trap, and probably other trap designs as well, is a function of six variables; 1) pollen productivity of the vegetation in the vicinity of the trap, including the genetically-controlled magnitude of pollen production of each species and the year-to-year pollen production variability due to environmental factors; 2) winds and weather, especially the direction, strength, and duration of winds as related to flowering times, and pollen wash-out during precipitation events; 3) topography of trap site that might affect local air movements; 4) trap design and efficiency of pollen grain capture; 5) laboratory techniques that reflect the skill of the technician and uniformity of methods; 6) the X-factor where the incorporation of insects or bird droppings or some other event, including trap vandalism, may result in unexplained erratic or unrepresentative pollen content. The trap-array study was designed to test the replicability of the Tauber trap design by eliminating or at least minimizing the pollen influx variability related to all of the above with the exception of the Tauber trap design itself (although the X-factor is always present). [During the study, the trap array was inspected frequently; tall stems of grasses and composites were observed bent over two of the traps, although the pollen content does not seem to have been modified by this event.]

The 10.5 percent standard deviation of mean pollen influx of the nine Tauber traps in the array is surprisingly high, and the variability of pollen percentages of individual taxa is higher yet. If these results are representative, a conclusion that can be made only with another traparray study, pollen influx and percentage values have a wide degree of either natural or trap-related variability. The significance of the study is two-fold: small differences in pollen trap percentage and influx values may not be significant, and the application of trap data as a modern analog to the interpretation of pollen acummulation rates in the sedimentary record may be valid only at levels of magnitude.
TABLE 1. Pollen counts and other data from nine-trap array, Denton
County, Texas.

Genus Trap number
 54 55 56 57 58 59 60

Pinus 4 8 12 6 9 14 10
Juniperus 80 100 109 89 70 69 60
Quercus 46 39 64 68 38 66 27
Carya 3 6 3 9 6 5 4
Ulmus 13 17 15 19 21 20 22
Celtis 3 6 2 3 2 5 -
Fraxinus 1 5 5 4 6 5 2
Salix 1 1 2 1 2 5 -
Populus 1 2 1 - 1 6 5
Juglans - - 2 - - 2 -
Carpinus - - - - 1 2 -
Castaena - - - - - 1 -
Alnus - - - - - 1 -
Corylus - - - - - 1 -
Prosopis 1 1 2 1 - - 1
Poaceae 21 11 14 28 25 15 30
Cerealia 20 25 18 17 39 33 56
Ambrosia 135 115 89 98 128 96 122
Franseria 22 17 18 20 16 20 22
Artemisia 3 3 3 1 6 2 3
Cirsium - - - - - - 1
Liguliflorae - - - - - - 1
Asteraceae 10 15 14 11 2 7 6
Chenopodiaceae 7 9 9 7 11 10 6
Amaranthaceae - - 1 - - - -
Ephedra - 1 1 - - - -
Brassicaceae 1 1 - - - - -
Apiaceae - 2 - 1 2 3 -
Morus - 2 - - - 1 -
Rosaceae - - 1 - - 1 -
Typha - 1 - - 1 - -
Cyperaceae - - 2 - - - 4
Undeterminable 15 6 11 7 10 6 16
Total unknown 13 7 2 10 4 4 2
Spike counts 225 198 249 201 172 216 228
Trap aperature
 (sq. cm.) 18.6 18.9 18.9 18.8 18.9 18.9 18.8
Total pollen
 influx/sq.
 cm./yr. 8615 9635 7661 9541 11091 8832 8411

Genus Trap number
 61 62

Pinus 10 6
Juniperus 91 96
Quercus 58 40
Carya 10 4
Ulmus 19 21
Celtis 3 1
Fraxinus 2 4
Salix 4 4
Populus - 1
Juglans - -
Carpinus - -
Castaena - -
Alnus 1 -
Corylus - -
Prosopis 1 -
Poaceae 16 14
Cerealia 20 22
Ambrosia 95 115
Franseria 21 15
Artemisia 2 9
Cirsium 3 -
Liguliflorae - -
Asteraceae 15 23
Chenopodiaceae 10 15
Amaranthaceae - -
Ephedra - -
Brassicaceae - -
Apiaceae - -
Morus - -
Rosaceae 1 -
Typha - 1
Cyperaceae 1 1
Undeterminable 8 4
Total unknown 9 4
Spike counts 209 209
Trap aperature
 (sq. cm.) 18.8 18.7
Total pollen
 influx/sq.
 cm./yr. 9176 9225

Pollen sum from each trap = 400, including "Cerealia," "indeterminable,"
and "total unknown" counts.


LITERATURE CITED

Andersen, S. T. 1980. Influence of climatic variation on pollen season severity in wind-pollinated trees and herbs. Grana, 19:47-52.

Hall, S. A. 1990. Pollen deposition and vegetation in the southern Rocky Mountains and southwest Plains, USA. Grana, 29:47-61.

Maher, L. J. 1972. Nomograms for computing 0.95 confidence limits of pollen data. Rev. Palaeobot. Palynol., 13:85-93.

Markgraf, V. 1980. Pollen dispersal in a mountain area. Grana, 19:127-146.

Mosimann, J. E. 1965. Statistical methods for the pollen analyst: multinomial and negative multinomial techniques. Pp. 636-673, in Handbook of paleontological techniques (B. Kummel and D. Raup, eds.), W. H. Freeman, San Francisco, xiii + 852 pp.

Solomon, A. M., and Silkworth, A. B. 1986. Spatial patterns of atmospheric pollen transport in a montane region. Quaternary Res., 25:150-162.

Tauber, H. 1974. A static non-overload pollen collector. New Phytologist, 73:359-369.

______. 1977. Investigations of aerial pollen transport in a forested area. Dansk Botanisk Arkiv, 32 (1):1-121.

STEPHEN A. HALL

Department of Geography, University of Texas at Austin, Austin, Texas 78712
COPYRIGHT 1992 Texas Academy of Science
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Author:Hall, Stephen A.
Publication:The Texas Journal of Science
Geographic Code:1U7TX
Date:Nov 1, 1992
Words:1881
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