Eastern Mojave Vegetation Autecology of Desert Elkweed Frasera albomarginata S. Watson (Syn: Swertia a.) Gentianaceae in the American Southwest (Continued)  
 

Tom Schweich  

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Topics in this Article:
Introduction
Literature Review
Field Work and Methods
Results
Taxonomy
Distribution
Growth Habits
Relationships to Soils and Other Plants
Life History
Discussion
Summary
Literature Cited
Appendix A -- Field Data
Communications Received.
 
This paper was originally presented at the 1999 Desert Research Symposium at the San Bernardino County Museum. The research is ongoing and the paper has been updated as new information becomes available.

You may notice a little schizophrenic appearance to names as I abandon Swertia as the genus and migrate to Frasera.


 

Field Work and Methods

 

Locations: Pinto Mountain. Wild Horse Mesa.  

My field work to date is to establish and monitor one 5x5 m experimental plot each at the two sites at Wild Horse Mesa and Pinto Mountain. The plots were established April 29-30, 1996.
  I established my experimental plots subjectively. After some reconnaissance of areas where I knew the species to grow, I selected areas of moderate to high F. albomarginata density that were near the centers of areas of occurrences. Sites at the edges of the species' occurrence or sites that were peculiar or unusual were avoided.
  One location I considered was an old road and the cut bank on the upslope side of the road. The species is often found in disturbed locations and it may spread easily into them. This would be a good location for an experimental plot if I were studying the colonization of disturbed places by the species. However, I am working on baseline autoecology, i.e., how the species grows in its natural undisturbed habitat. Therefore the road and cut bank were not selected for an experimental plot location.
  Once the sites were selected, I laid out a centerline that passed through the center of the area. I laid out the centerline up and down slope, so that I could prepare a slope profile. The centerline extended from to bottom to the top of the areas selected, and was 50 m long at Wild Horse Mesa and 30 m at Pinto Mountain. The endpoints of the centerline are marked by steel reinforcing bar.
  Near the middle of the centerline I selected a 5 m section. By measuring 2.5 m in both directions from the centerline, I defined a 5 m by 5 m plot. The corners of the plots are marked by steel reinforcing bar. Along each side of the plots I also placed fiberglass stakes at 1 meter intervals. These help be measure the locations of new plants in the plots.

Full Size ImageExperimental plot in Frasera albomarginata, north slope of Wild Horse Mesa.  
The photograph at left shows a general view of the plot at Wild Horse Mesa. The rocky white soil is derived from lacustrine limestone informally known as the Winkler Formation. The white stakes mark individuals of F. albomarginata which grow in the open spaces between the Utah Junipers (Juniperus osteosperma) and Single-Leaf Pinyons (Pinus monophylla). The visible shrubs are California Buckwheat (Eriogonum fasciculatum).

Full Size ImagePhotograph of staked Frasera albomarginata.  
Each individual of F. albomarginata in the experimental plots were located and marked with a numbered stake, as shown in the photograph at left. The stakes are made of 1/4 inch (6.4 mm) diameter fiberglass rods which have been trimmed to 14 inches (35 cm) in length. They are sharpened at one end with a pencil sharpener to permit insertion into the soil and have a numbered band glued to the other end. The bands are numbered from 1 to 100, and can be further identified by background colors. For more details about the stakes, see my page on "How to Mark a Forb."

Full Size ImageWorking in the experimental plot on the north face of Wild Horse Mesa.  
I constructed a 5 m measuring rod from 1/2 inch white plastic water pipe. The measuring rod is in four 1.25 m sections and joined together with plastic unions. The ends of the measuring rod have 4-way plastic unions that fit over the stakes placed along the sides of the experimental plots. Markings are placed on the pipe every 10 cm. When working in my plots I place the rod transversely. This helps me organize my data collection tasks, and assists me in measuring the location of new plants of the species.

Full Size ImageThe author collecting data on the north face of Wild Horse Mesa in May 1988.  
Since the plots were established, they have been visited twenty-six times:
  • October 18-19, 1996.
  • April 29-30, 1997.
  • October 3-4, 1997.
  • March 14-15, 1998.
  • April 28-29, 1998.
  • May 23-24, 1998.
  • September 19-20, 1998.
  • April 21, 1999.
  • May 29, 1999.
  • September 26-27, 1999.
  • April 27, 2000.
  • June 5, 2000.
  • September 22, 2000.
  • April 24, 2001.
  • May 26, 2001.
  • September 16, 2001.
  • April 23, 2002
  • May 26, 2003
  • May 25, 2004
  • May 28, 2005
  • October 15, 2005
  • June 7, 2006
  • June 4, 2007
  • May 28, 2008
  • June 2, 2009
  • June 2, 2010
  At each visit the status of each plant noted. Analysis of this data continues. I plan to continue to examine each plot several times per year over a period of years in my continuing study of the species.
  The data collected for each plant during each visit are:
  • Location, x-position and y-position in the measured plot.
  • Species, always Frasera albomarginata in this study.
  • Dimensions, the longest horizontal dimension, the dimension at right angles to the longest, and the height.
  • The number of basal leaves. F. albomarginata forms a rosette of basal leaves until it flowers.
  • Whether prior year's leaves can be seen. The intent of this datum would be to determine whether this individual is a new seedling, or a suceeding year's rosette. In practice, I believe that absence of prior year's leaves is probably not a reliable means of determing that a plant is a 1st-year rosette.
  • The diameter of the rosette.
  • Whether any form of inflorescence (flower stalk or buds) is visible.
  • Whether predation has occurred on the inflorescence, i.e., has something eaten it.
  • Life Stage. At present I am working under the assumption that there are seven stages in the life history of F. albomarginata.
    • 1st-year rosette
    • Dormant
    • 2nd-year rosette
    • Bud
    • Flower
    • Fruit
    • Dead
  • Comments
  I don't think it is possible to tell whether a F. albomarginata plant is "Dormant" or "Dead" when examining the above-ground parts of the plant in the field. It may be observed with dry leaves or no leaves at all. In such a state, is it dormant or dead? Presumably the caudex could be examined and a determination of "dormant" made if the caudex were still fleshy. However, this would require removal of soil from around the caudex and would disturb the plant.
  I have resorted to assigning "dormant" or "dead" status based upon repeated observations over a period of time. If a plant that I have previously staked is observed to be dormant or above-ground parts cannot be found over a period of one year then it is presumed to be dead. It is presumed to have died as of the first observation it was recorded as dormant. Since I have been observing populations twice a year, in April and October, there will be three observations of "dormant" or "not found" before a plant will be recorded as "dead." Once a plant is identified as "dead," the stake marking its location is removed.

Full Size ImageFrasera albomarginata worksheet.  
A sample page from the worksheet is shown in Figure 14. The data are entered into a Microsoft Access data base upon return from the field. The field data are published in Appendix A.

Other articles: Eastern Mojave Climate Climate  

Weather data will also be important as the study progresses. Summary climate data is available at my page on the Climate of the Eastern Mojave Desert. In addition, as my study is unfolding, it begins to look like year-to-year precipitation may be significant in population dynamics of F. albomarginata. Therefore, I suspect that current weather data will be needed before this study ends.
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If you have a question or a comment you may write to me at: tas4@schweich.com I sometimes post interesting questions in my FAQ, but I never disclose your full name or address.  


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Date and time this article was prepared: 4/9/2017 9:14:05 AM