While walking through Western Woods an observation made was that the ecosystem on the edge of the forest was different from that which was farther into the forest. Even on our short work in Western Woods, we recognize differences between the vegetation compositions in these two areas. From this our group developed our hypothesis. We expect to find a greater diversity of species within Western Woods than on the outside. Therefore, we expect that the trees, shrubs, and herbaceous plants on the edge of the forest to be younger, have a smaller circumference, and a less diversity of species. We feel this is a good question for us to research because we have the means to accomplish this task at hand. While we know there may be many different aspects of the trees and forest that could be tested, such as the height, but because of our limited knowledge, resources, and time, we feel the task described above is one that we can not undertake. Throughout this experiment, while discovering the differences in Western Woods, particularly by the Western Lodge, we also hope to gain knowledge about this topic because edge effects are such a widespread problem in the world today. We find this interesting because there is so much deforestation happening, and we realize that the loss of trees is worse than society understands. Society does not understand that the driving force behind edge effects are from human interactions.
Relevance of Our Research Question
A group of researchers studied woodland edges at various distances from other habitats. They used built out and natural habitats for comparison for data collection. They composed highways, projected reserves, and accessible public lands. Edges were tested less than two hundred fifty feet, between two hundred fifty-one and six hundred feet, and greater than six hundred feet away from the effected habitat. They found that the edge effects were a high edge, a moderate edge, and low to no edge, respectively. The study however, also shows that these intervals were for this specific experiment and that though they have value pertaining to other experiments, they are not one hundred percent accurate (MSHCP 2002).
To get a better understanding of what “edge effects” truly are, we looked for other sources to explain this term. An edge is described as a meeting point of two habitats; “the ecological effect that occur at the boundaries of ecosystems, these includes changes in species composition, gradients of moisture, sunlight, soil and air temperature, wind speed, etc…Many edge effects have negative consequences” (Natural Areas 2000).
A woodland area is created by two different habitats, an edge habitat and an interior habitat. These two habitats are considerably different. The interior habitat has not been touched by the edge effects, while the edge has been. This edge habitat can reach from a few to several hundred feet in to the woods (Land-Use Planning).
One article showed the importance of this problem. An author from the United Kingdom wrote a letter to an organization about this issue. Law does not protect eighty-five percent of ancient woodlands. These woodlands could be cut down or otherwise destroyed. The remained fifteen percent are only under a status of “Site of Special Scientific Interest.” One idea given to help prevent these habitats from being destroyed is to get up buffer zones, areas that cannot be changed (Graham).
Materials and Methods
Originally, we had planned to test our hypothesis that states that the trees within the forest will be older, have a larger circumference, and will have a greater species diversity by using transects. However, the wealth of information collected inhibited us from analyzing and forming results in accordance to the age and circumference. Even though we collected the circumferences of the trees and saplings, our group thought that it was more important to concentrate on the diversity of the species. We planned to sample five twenty-meter transects across the edge of Western Woods. We also left two meters between each transect to be able to identity each location easier. However, in the end, these transects were irrelevant. Within each transect, within a one-meter width, we measured the circumference of each tree, identified the species of each tree and vegetation composition, and took account of the number of each species there were. We chose to measure the circumference of trees that were one meter from the ground. When involving the class, we had them measure the circumference at breast height. After collecting all the needed data from the edge of the forest, we originally planned on doing the same data collection 100 meters into the forest. However, because of restrictions of safety, we measured 50 meters into the forest rather 100 meters.
Our sample will be statistically sound because we are testing a large enough sample of species. We went deep enough into the woods to be sure that our second measuring line would not be impacted by the edge effects.
The first section of our test included the few trees and vegetation composition that have experienced edge effects. This sample is vital because we need a large sample of trees from the edge to reach a sound conclusion. Testing a total of 100 hundred meters across the forest edge will ensure to give us a sufficient sample. The second part of our test included collecting data on the trees within the forest that are unaffected by the edge effects. This is also vital so we have a large sample of trees untainted to compare to those trees that have experienced the edge effects.
We realize that in a natural setting these species do not grow in straight lines. For this reason, we tested a width of one meter within each of transect and 50 meters in to the woods to get a good sampling. We determined the species of the trees by using books and tree guidelines.
One aspect we will not be testing that could be sampled is the height of the trees. We did not do this because it was not feasible. We did not have the means to accomplish this data collecting.
For this experiment we tested trees, saplings and prominent vegetation composition. We knew that there were a wide variety of other plants that grow within and on the edge of Western Woods, but originally we thought that collecting data on all of these would be out of our time constraints. However, we felt it was necessary to also take note and count the number of the different species of vegetation that was prominently growing on the edge of the forest. By testing both the trees and vegetation, we feel that is gave us the answer that we were searching for.
Along with our own knowledge, we asked for advice from our professor, Vivian Negron-Ortiz and our teaching assistants. Their advice gave us insight on the best sampling methods and how many of these samplings we should do.
Our results are unbiased. We will not be conducting a random sampling method, making the results more impartial. All of the data we will be collecting is scientific, for they are measurements instead of judgments.
For our lab we needed few materials. The first item used was a large tape measure. This will be used to measure the circumference of the tree, along with the distance into the woods for the second sampling line. A second vital item was a book to help us identify tree species.
The class helped us to collect our data. We showed them how to measure the circumference of the trees along with how to identify the tree species. To make sure that the data collected by our peers was reliable and consistent, we gave a demonstration of the measuring techniques. We also supervised the data collecting to make sure the class was using proper methods and being honest. As well, the class was also involved in identifying the species inside the forest.
Timeline of Events
Saturday & Sunday October 5th and 6th
* Trip to Science library for references and tree- finding guides
* Measured and plotted the transects to be studied
Tuesday & Thursday October 8th and 10th
* Posted critical reviews
* Posted progress reports
* Collected data – measured the circumference of trees on the edge
* Collected data – measured circumference of trees inside the forest
* Class time used to identify species on the edge
* Finalized all “unknown” species
* Met to modify methods in our proposal
* Class time used to identify species on the inside of Western woods
* Finalized all “unknown” species
* Met with peer science tutor for help with Stat View
* E-mailed Jessica and had her send the group photos of the class
* Worked in computer lab with Stat View to analyze results
* Modified Stat View results
* Finalized paper
* Printed out graphs and pie-charts
* Download the Help Sheet
* Final report preparation
* LABS DUE!!!!
-Post to web
-Make Mac copy on floppy disk
-Include a paper copy
Data Sheet 1:
Outside of Western Woods
Species Name Amount Found
Data Sheet 2:
Inside of Western Woods
Species Name Amount Found
After the data was collected, the group began to analyze the information from the observations and began to realize that the results would be based solely on what we saw and took note of while we were collecting the data. We found that there were more species living on the edge than the inside of the forest of Western Woods. Our hypothesis stated that there would be a greater diversity of species on the inside of the forest, rather than on the outside, however, when we began to look at the data, the group realized that our hypothesis was not correct.
In order to test our results, the group decided on three different tests to calculate. The first test that we decided to do was a statistical one. However, in comparison to our peers who prominently used the t-test to calculate the difference of the means of the two groups being that were being tested, because of our data, we had to use a different test. This unavailability to use the t-test was indeed frustrating, however when introduced to the Spearman Rank Test, our data began to make more sense. This test compares the rank order of the species abundance between the outside and the inside of the Western Woods. This is beneficial to us because it allows us to know whether or not there is a statistical difference between the two sets of data that we collected. The null hypothesis for this test is that there is a difference between the outside and the inside. After running this test, a p – value of .62 was calculated (Table 1). Since this value is higher than .05, we fail to reject the null hypothesis. Therefore, there is a statistical difference between the presence and absence of the species found in the outside and the inside of the forest.
The second test that was performed was the Shannon Weiner Index. This is a measure of species diversity that considers species richness and relative abundance. The number that is the highest after doing this test is the one that is most diverse. The inside of the forest had a value of .6705, while the outside of the forest had a value of 1.4804 (Table 2). Since the inside of the forest had the higher value, it is the one that is the most diverse.
The Community Similarity Index was the final test that we used to measure the ecological diversity. Values of this test can range from zero to one. One expresses that the two communities are identical and zero means that the two communities have nothing in common. After completing this test, the number that was obtained was .417. (Table 3). This number means that each community is unique and does not have similar species living in them.
In order to make our results more visible, two pie charts were constructed. One is for the outside of the forest while the other is for the inside. The pie charts state which species lived in either the outside or inside of the forest, and how many of each species there were (Figure 1). We also included a bar chart to show the total amount of trees and shrubs (Figure 2). Just by looking at the charts one is able to tell that there are more species living on the outside than on the inside. A table of the amount of different species that were found in the outside and the inside of the forest was also added to our collected data (Table 4).
Discussion and Conclusions
After examining the results of our project, we discovered that our hypothesis was incorrect. The results proved that there was actually more diversity on the outside of Western Woods than on the inside. At first this surprised us, but after thinking about this more thoroughly, we were able to understand why this was so.
By doing this project the group members were able to come to conclusions based on the background research that was done, our own knowledge that was gained by doing this lab, and the analysis of the data. A woodland area is created by two different habitats, an edge habitat and an interior habitat. These two types of habitats are considerably different. The edge of a forest includes changes in species composition, gradients of moisture, sunlight, soil and air temperature, and wind speed (Natural Areas 2000).
In our results we found that there was more diversity on the outside of a forest than on the inside. On the outside of the forest we found mainly shrubs that were not very tall. On the inside of the forest large trees were the most commonly found species. This is because the edge provides the type of living environment that shrubs need, one that is different than that needed for tree growth. “Edges have complex, species-specific effects on tree establishment and growth that can influence the spatial pattern and species composition of forests” (American Journal of Botany).
Shrubs reproduce and grow very quickly. They also do not take up as much space as tree species and do not need as much water or sunlight. On the other hand, the type of species that is found on the inside of the forest grows slower and does not reproduce as often. Therefore the species found on the inside of the forest are taller than those found on the outside, but are not as abundant. Also, a lot of different species are able to grow on the edge because that type of environment is more suitable for a lot of different shrubs. Trees require a very specific type of habitat and environmental conditions.
Even though the results make sense, there were sources of error in this lab. The first error is the restrictions that we had due to the actual size of Western Woods. We actually should have started testing for the data further inside of the forest where the trees started. That way we could have tested the same group of species (trees) and the different types of that species found instead of two totally different types of species (trees and other vegetation). We also discovered that the transects were not needed. The first transect was L shaped which could have had an influence on the type of species that were found there. A final source of error is that we had other students help us with our results. The other students may have identified the same species differently than a different group of students.
This project fits in with other scientists’ research. One group of researchers studied forest edge effects at various distances from other habitats. They found that the range of edge effects varied with the distance that it was from other habitats. Another group of researchers tested edge effects with tree seedlings. They used transects similar to ours, and placed tree seedlings into these transects. Their results proved that trees could grow better inside of the forest (American Journal of Botany). This information goes right along with the results that we found.
There are many questions that we would want to be answered. Trees are very important to the environment and to humans, and forests are constantly being chopped down. Therefore, there are more edge effects, and trees do not grow on the edge. We were wondering if people are becoming more aware about the causes of having a forest edge and what people are going to do about this in the future. We were also wondering whether there are a lot of different types of species found on the edge or if the species that we found were the ones that are usually most prevalent.
In the future we would suggest testing a forest that is very large and also testing the same group of species. For example, only testing trees or shrubs, not both. We also suggest testing more than just diversity. Another area that could possibly be tested is the circumference of the trees that are found. This will tell the age of the trees and will also let the researcher know whether or not trees live longer on the outside or the inside of the forest.
In conclusion, we feel that “Living On The Edge” was a very successful student generated lab. We were able to learn a lot about the types of species that grow on the outside and the inside of the forest. Even though there were some sources of error, we were still able to have correct results. A lot of information about the harms that an edge can cause was gained. We are now more knowledgeable about this subject, and can also inform others about the dangers of edge effects.
List of Works Cited
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American Journal of Botany. 89, no. 3 (Mar 2002): p. 466 – 471.
Brockman, Frank C. Trees of North America. Golden Press. New York. 1968.
Graham, Bradley. “Letter to Woodland Trust.” 8 Feb 2002. 24 Sept. 2002.
Natural Areas: Protecting a Vital Community Asset; glossary.” 19 April 2000. 24 Sept.
“Land-Use Planning in Oak Woodland.” Integrated hardwood Range Management
Program. Update 2000. 24 Sept 2002.
Petridges, George A. Eastern Trees. Houghton Mifflin Company. Boston. 1988.
Petridges, George A. Trees and Shrubs. Houghton Mifflin Company. Boston. 1988.
“The MSHCP Reference Document.” Riverside Co. Integrated Project. Update 2000. 24
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