Biology in the Real World

Written Assignment 2: Biology in the Real World

This assignment will give you the opportunity to participate in ongoing scientific research. For the past several years, I have been involved in ecological research in old-growth forests in Wisconsin. In many areas the forest floor is dominated by a grasslike species, Pennsylvania sedge (Carex pensylvanica). The sedge may exclude other ground species by interspecific competition, which may decrease biodiversity. The Penn sedge “lawns” are probably caused by selective herbivory by an abundance of white-tailed deer. The deer do not like the sedge but consume most other ground plants. [See OLI Module 51 for information on competition & herbivory and Module 53 for biodiversity.] Another problem in the forests is that dominant trees, such as white pine and sugar maple, do not show successful reproduction to replace old pines and maples that die.

With support from a UMUC Faculty Research Grant to create this assignment, I collected data this summer that you can use to address three hypotheses-

Hypotheses:

A. Pennsylvania sedge inhibits regeneration of white pine
B. Pennsylvania sedge inhibits regeneration of sugar maple
C. Pennsylvania sedge decreases biodiversity

Methods of Data Collection

During 2-4 August 2013, I recorded the presence of all ground species in transects of adjacent 2- x 2-meter quadrats across my permanent study plot at Trout Lake Cathedral Point, Vilas County, Wisconsin. In ecology, a quadrat is defined as a sample area and a transect is a sample line. Figures 1 and 2 illustrate the method of transects of continuous quadrats. I estimated the percent cover of Penn sedge within the quadrats and counted all established tree seedlings (defined as > 20 cm in height and < 1 cm in diameter at breast height). This site was chosen to test the hypotheses because Penn sedge dominated the ground cover in portions of the plots but was absent in other parts.

A total of 189 quadrats were sampled within a forest dominated by trees of sugar maple, red oak, and red maple. Interestingly, seedlings of white pine were most abundant, with a total 124 plants in the quadrats. There were 95 sugar maple seedlings. Other tree seedlings were few, so we will confine our analyses to white pine and sugar maple. White pine, common in a stand adjacent to the study plot, has shown a recent burst of reproduction in the forest. (If interested, see Riege 2012, “Surge in regeneration of Pinus strobus L. in three Wisconsin forests not projected by past demography,” Journal of the Torrey Botanical Society 139:299-310.)

Figures 1 & 2 are attached .jpg files

Figure 1. Transect line entering “lawn” of Pennsylvania sedge, with scattered white pine seedlings.

Figure 2. Quadrat of 2 x 2 meters created by centering 2-meter sticks on transect tape. This quadrat on a sedge boundary contains small sugar maple and white pine seedlings.

Testing the Hypotheses – Data Analysis

The raw data for you to use to test the hypotheses are presented on an Excel spreadsheet with the file name “UMUCRiegeSedge.” Listed for each quadrat are the percent cover of Pennsylvania sedge, the number of white pine seedlings, the number of sugar maple seedlings, and the number of species. [Number of species in an area is called “species richness” and is a main component of biodiversity, see OLI Module 53.] I caution that this exercise differs from those typically found in an introductory science course. It is not a canned lab that is designed to illustrate a process. In other words, the outcome may or may not support the hypotheses. The results may be “messy” and not as clear as designed labs. I urge you to be creative in your approach to testing the data – there is no one correct method of analysis.

So, you ask, where can I start to make sense of this big spreadsheet full of numbers? I would suggest one good way to begin is to tabulate the data by categories. For example, you might classify the quadrats by percent Penn sedge, such as 0-25%, 26-50%, 51-75%, 76-100%. Then you can tally or average the seedling and biodiversity numbers for each sedge category. If you look at scientific papers, you will see lots of tables and graphs. When graphing data, the independent variable (cause) is on the x-axis and dependent variable (effect) is on the y-axis. Our hypotheses have Penn sedge as the cause, hence percent sedge cover will be on the x-axis and seedling/biodiversity data on the y-axis. In your report, use graphs and/or tables, as well as a written summary, to present your analytical results.

Do not be limited by my suggestions for categories or analysis. Be creative.

Conclusions and Discussion

Summarize your analyses by concluding whether the data support or disprove Hypotheses A, B, and C. Then discuss how your conclusions might relate to the many factors that influence forest composition. For example, one factor not measured that may affect our data is the amount of shade. Although the study area had similar tree composition throughout, some areas contained thicker shade, which might decrease both sedge cover and species richness, thus obscuring any relationship between the two. Ecology is very complex, that’s why it is so much fun (but it makes it very difficult to verify causes and effects). Again, be creative in the discussion. Shade is just one example of many factors that influence plant growth.

One experiment leads to another in the scientific method. In your discussion, use your conclusions to generate at least one new hypothesis that could be tested to further add to our knowledge of the effects of Pennsylvania sedge.