Biology 2108 Laboratory Exercises: Variation in Natural ...

Biology 2108 Laboratory Exercises: Variation in Natural

Systems

Ed Bostick Don Davis Marcus C. Davis Joe Dirnberger Bill Ensign Ben Golden Lynelle Golden Paula Jackson Ron Matson R.C. Paul Pam Rhyne Gail Schiffer Heather Sutton

Kennesaw State University Department of Biology and Physics

LABORATORY 4 Ecology: Variation within Ecological Communities

(Part 1)

OVERVIEW OF LAB Observations: Forests within the same region often vary dramatically in species composition. This is easily observed within our county, where forest patches vary in many ways, the most obvious being the relative number of pines and hardwoods. A possible explanation for these differences comes from observations on changes in species composition over long periods of time. In many ecosystems, species composition changes over many years in fairly predictable ways. This process is known as ecological succession.

To explain difference in the communities of two nearby forests stands we will test the following hypothesis based on this ecological succession model:

Forest stands that differ in the length of time since major disturbance will differ in species composition.

For forest communities in this region, the last major disturbance was most likely agriculture. By the early 20th century, most of the land in the region was agricultural, with cotton as the major crop. With severe soil erosion and infestation of the cotton boll weevil, farming became unprofitable and the land has slowly returned to forest.

Over the next two weeks we will measure physical and biological factors within two nearby forest stands to test the model of ecological succession. Specifically we will address the following questions:

Do the two forest stands differ in the time since disturbance (and if so, which one is "older")? (Week 1)

How are these two successional stages different in species composition (hardwood vs. pines, amount of undergrowth, species diversity)? (Week 1 & 2)

Can differences in environmental factors explain how ecological succession occurs? (Week 2)

SAMPLING IN FOREST AREAS A AND B The class will be divided into several groups and each group will sample plots in one of two different forest areas that appear to differ with respect to plant species composition (arbitrarily named Forest A and Forest B). Your instructor will show you the general areas within which plots (quadrats) will be established and sampled. Ropes have been divided into 10 meter units. To establish a 100 square meter plot, stretch a rope out on the ground in a square with the 10 m marks on the rope as the corners.

Each group of students will collect data in five 100 m2 quadrats in Forest Area A or B as follows:

- In order to estimate the relative "time since a major disturbance", we will measure the circumference of all pines found in the quadrats (on the assumption that the circumference reflects the ages of the pines). Because pines are abundant in each forest area and are primarily of a single species (the Loblolly Pine, Pinus taeda), we will use the age of these trees to determine which forest is older (i.e. existed longer since the last major disturbance).

- In order to determine how are these two successional stages different in species composition, count all pines and of all hardwood trees that are over 45 cm in circumference in each quadrat. Pine seedlings are more tolerant of high light and dry, poor soils than are hardwoods.

RAW DATA TABLE

Plot 1

No. of Pines >45 cm

No. of Hardwoods >45 cm

Circumference of all pines (cm):

Plot 2 Plot 3

Plot 4 Plot 5

COMBINED CLASS DATA

The pine circumference data from the two forest areas will be compared using a t-test. This will be done in order to confirm our assumption that the two forest areas chosen differ with respect to "time since a major disturbance".

Mean Circumference of Pines in Forest Area A: _______ (cm) Standard Deviation: _______

Mean Circumference of Pines in Forest Area B: _______ (cm) Standard Deviation _______

t-test P-value: ________________

The numbers of pines & hardwood trees (> 45 cm) in forest areas A and B will be compared using a chi-square contingency table test of independence as follows:

Area A

Area B

Pines

Hardwoods

chi-square test P-value: ____________

LABORATORY 4 Ecology: Variation within Ecological Communities

(Part 2)

OVERVIEW OF LAB In the second week we will return to the field and collect data on a variety of environmental factors. These "descriptive data" may then be examined in order to determine whether they support the ecological succession model that we tested in the previous week.

SAMPLING IN FOREST AREAS A AND B This week, each group will collect data from three 100 meter2 quadrat plots within either forest area A or B.

1. Determine the amount of light at the four corners of the plot and at the center of the plot using a light meter.

2. Measure topsoil moisture (using a moisture meter) at several cm into the topsoil.

3. Measure top soil temperature (using a thermometer) at several cm into the topsoil.

4. Measure top soil depth (using a ruler)

5. Count the number of trees in each plot (do not include undergrowth plants).

6. Examine the leaves, bark, and branching pattern of the trees to determine the number of species of trees in a plot. Assign a number to each of the tree types ("species") you can distinguish and tabulate the number of each type of tree in the plot. Note that we need not identify each species by name, with the exception of three species: pines, tulip poplars, and dogwoods. These species are easily identified - your instructor will show examples in the forest.

7.Count the number of undergrowth plants as follows: choose one of the four sides of your quadrat and count every undergrowth plant that touches or is below or above that side's rope. N.B.: the class as a whole must be sure to establish clear criteria for distinguishing between "undergrowth plants" and "trees".

Repeat the above procedure for your second and third plots. Measure the same variables that you measured in the first plot.

SAMPLING IN THE PRE-FOREST AREA Each group (regardless of whether they have been assigned Forest Area A or B) will also sample physical parameters in a recently disturbed area behind the Science Building. The environmental conditions present in Forest Areas A and B have presumably changed since the tree species in each of those forests first germinated. In order to more closely approximate the conditions under which the forest first developed, we will select an area that is younger (i.e. less time since disturbance) than each of the forest areas examined in the previous week. This "pre-forest" area with very young pines can be thought of as the "early successional" conditions from which younger of the two forest areas developed. The younger forest from last week can be thought of as the "later successional" conditions from which the older forest developed.

Each group should "randomly" select two points in this "pre-forest area" and measure the following parameters at each of these two points:

light soil moisture soil temperature soil depth.

Return to lab. Data from all groups will be compiled and data analysis will be discussed

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