The Future of Peabody Woods
A Study of Age Structure
Question: What will the true content of the woods behind Peabody Hall be 100 years from now? This question involves finding whether Western Woods is at it’s climax stage of succession by testing the dominant tree species.
Introduction: Since our purpose is to determine which trees will or will not be dominant in the Western Woods, we formulated our hypothesis using research done on prominent species of trees in southwestern Ohio. To do this, we researched the concept of forest succession. Succession is the progressive replacement of one ecological community by another until a climax community is established( Webster). The climax of a community is the stable and self-perpetuating end stage in the ecological succession of a plant community (Webster). The Clementsian view is generally used in textbooks therefore we will base our lab upon its’ theories. Clements found that succession occurs in discrete stages and that transformation between these stages happens over a short period of time. He also found that species tend to change simultaneously from small to large with a single climax. The stages involve the invasion of open ground by pioneer deciduous trees; the introduction of conifers to produce a mixed community; the development of a young rainforest; and the emergence of a mature climax forest. The nature of the area also will define who establishes within it. Species interactions dominate and that interactions outcome dominates. For instance, plants alter the environment making room and creating proper soil conditions for other plants, which makes changes for allowing other plants to take hold. These are important points because under the conditions mentioned, it is theoretically possible to predict the course of succession. Age structure of trees can be used to predict dominance in the next generation by assuming that the saplings will come to dominate. Further, incorporating size-specific mortality rates strengthens succession assertions. This knowledge can be used to recognize the areas’ vegetative patterns and further help to predict what the entire environment will resemble in the future. Also, this experiment could bring an ecological classification to Western Woods as a whole.
Hypothesis: There will be no significant shift in the dominant species (any plant that by virtue of its abundance, size, or habits exerts such an influence on the conditions of an area as to determine what other organisms can live there) of trees in Western Woods. The dominant species will be analyzed by considering the relative density, the relative frequency, and the relative basal area to find an importance percent. The concept of succession will be analyzed by the dominance abundance of younger tree species and seeing their relationship to the already dominating species.
Materials: Tree identification guides, a data sheet, and a tape measure
Research Design and Methods: To get a random sample, our group will go out into the woods before the class to plot out uniform areas. We will do this by measuring an edge behind Peabody to be 100 m. Then, from our random pick of numbers chosen from a random number chart (supplied by Dr. Vankat), we picked 25m in from the left of the 100m measurement. (The green strip on the attached map is where the 100m line will be measured) Following the chart, 8m will be measured back into the woods. This will be the center of our first 10m x 10m plot. From this plot five more uniform areas will be sectioned off. These will all be 25m from one another (see picture). There is the option to do a nested plotting tequnique within our plots, but for our lab and the sake of time we will not consider this. Nested plots are preferred by only some botanists because the nested plot takes into account the smallest trees (in our lab this would mean the trees under 5 cm). Nested plots section off smaller parts of the entire plot. Within these plots, data is collected on all sizes of trees. In the entire plot, including the nested areas, only data from trees over a certain diameter are collected.
The class will be divided into even groups that will fill six grid plots. In these plots, the students will record data from all trees that are above breast height (4.5 feet) and are greater than 5 cm in diameter (19.6 cm in circumference). First, using the tree guide, decide what species the tree is. Record the species. Next, measure the circumference of the tree at DBH (diameter at breast height). Record this number. Repeat this procedure for all the trees within the plot.
Analysis: Referring to the analysis sheet, fill in the absolute and the relative values.
A) Absolute density (Den.) = (individuals/ ha) number of individual species divided by the total sampling area.
B) Absolute frequency (Freq.) = (%) number of plots where individual species is sampled / total
number of plots sampled.
C) Absolute basal area (B.A.) = (m^2/ha) (meters square divided by the total sample area). This can be calculated by multiplying the area of the tree at breast height times 4.5ft (137.16 cm) which is the height at breast height. This calculation will discard any flaring at the base of the tree.
Units for relative values and importance percentages = %. When finding basal area, assume that the individual trees are circular.
A) Relative density (Den.) = total number of individuals of one species / total
number of individuals of all species X 100.
B) Relative frequency (Freq.) = frequency of individual species / total of
frequencies for all species X 100.
C) Relative basal area (B.A.) = basal area for individual species / total basal
area for all species X 100.
Importance percentage = relative density for individual species +
relative frequency for individual species + relative basal area for
individual species / 3.
From the Importance value, one can tell the structure of the forest at the present time. The species with the highest I.P. is the one that is dominating the forest. Importance value always equals 100%.
When dealing with species “diversity” or heterogeneity, one can understand this concept through qualitative descriptions. The question when looking at data is, “which one is more diverse?” This can be explained through richness and evenness values. Richness is defined by S and S values. The S = the total number of species counted. Referring to community A, below, the S = 6 because six different species were sampled. The S = the average (mean) number of species per sample. This would be calculated by P + P + P +... P / (n). The P = relative importance of the (i) species. The evenness value is the actual diversity of the community / the maximum potential of the community, but for this experiment we are avoiding this process.
When calculating diversity, there are two types: Simpson’s Index and Shannon’s Index. The Simpson’s Index favors or weighs the more abundant species in the calculations verses the Shannon Index that weighs the less abundant species. This project will use the Simpson’s Index because the dominant species is what is wanting to be found.
The definition of the Simpson’s Index is the theory of randomly picking 2 plants and having them be the same species. The symbol for this Index is (C) = p. For example in community A the values are:
species count
1 90
2 2
3 2
4 2
5 2
6 2
The C value of this set of data would be (.90) + (.02) + (.02) + (.02) + (.02) + (.02) = .81 = C. But to understand this value one has to find the reciprocal value (1/C). Therefore, (1/.81) = 1.2se. For the reciprocal value there is a label put on so we can understand that there is about 1.2 abundant species (se). The .90 value would represent the 1 part and the .02 values would represent the five other species. It is important to make these calculations when finding the diversity of the community.
When looking at the analysis sheet, one can predict the future of the forest. If there is a large amount of the same species with small values for the basal area then one can predict that that species is fighting to become the next dominant species in that forest.
Note: If we have any problem with canopy species or the question with whether one species will only reach a certain girth, Dr. Vankat volunteered his help with any additional information we need to analyze these factors.
Graphing: Graphing the data of the trees is shown on a size class graph. On the x-axis is the size classes (starting at 5 cm because that is the smallest diameter reading our data will accept), which is categorized every 10 cm difference. The categorizing of the range of centimeters is to accommodate any error relating to a slow growing verses a fast growing tree. Rates of growth could be from a clearing in the trees from a fallen tree, allowing more light to penetrate through the canopy, or maybe a low place in the topography, allowing more water to collect around certain trees. But for the most part, the range in area size will wipe out any of these factors. On the y-axis is the density of the individuals (individuals/ ha). Putting all the species on the same graph will give visual statistical value to compare the trees. In the picture below, the steepest slope will show an increase in the tree potential because there are many young trees in the population and those trees will fight to become more dominating. The flattest curve shows a decline in that particular species because there are few younger trees to replace the existing older trees. The medium curve in-between these two extremes shows a stable species bemuse there is an ample amount of young trees to replace the older trees, but not too many to surpass the number of already existing elder trees.
CONCLUSION
As was stated before, our hypothesis said that the dominant tree species in the Western Woods would not change within the next 40 years. We selected this hypothesis because we did not see much evidence of species diversity in our original research on the topic. And, having performed the sampling for the lab, we have found that our data supports the hypothesis that we originally put forth. We found the Western Woods to be largely made up of beech and maple trees, and our data indicates that it will not change much in the next 40 years. According to our data, the forest should not change much in the next 40 years for two reasons. First, the woods is not very diverse; it is composed mostly of young beech and maple trees, and the canopy is made up of mostly the same. Also, the forest is still in the middle of the succession process, and has not climaxed yet. Maples are the most commonly found tree, and many of them are young as well. Thus, if one species of tree were to be named as the dominant species at climax time, it would be the maple. In conclusion, the Western Woods is an environment that all Western students living on campus will come into contact with; whether through class exercises or just a walk on the trails. And hopefully this lab will be helpful in predicting just what kind of environment that might be for fututre students here at Western.
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