.
The article written by Peter Weiss discussed the various trajectories of leaves. Itprovided us with information regarding the history of research previously done on the study of leaf fall. There is a fascinating connection between the aerodynamics of leaf fall and any other forms of flight such as the "maneuvers of fighter-bombers or bees." This article also became the basis of our class demonstration because it talked about various experiments done relating to leaf fall. There have been many studies done by video taping and analyzing the falling behavior of rigid strips of plastic or metal in water or other viscous fluids. This is the type of experiment we demonstrated during class. The article was a wonderful source for our lab because it provided us with an enormous amount of information concerning the different patterns of leaf trajectory. It was also beneficial because it helped us to understand why certain leaf were dispersed more greatly over the ground's surface area under the observed trees. The second two articles found on the World Wide Web were related to the identification of different leaf types. While collecting our leaves, we found there to be an abundance of different types of leaves stuck in our nets. Thus making the data collection of our lab quite timely and tedious. We had to sort all of the leaves collected in our nets by determining which leaves fell from our tree species. The two articles from the Internet described explicit detail of the variations in leaf type, so that we were better able to determine which leaves were in fact ours. Even though our research takes place outside of Boyd Hall, it can also be viewed from a much larger perspective. The simple comparison of the three trees' leaf drop-rates can correlate with trees from around the world. This lab is designed to become a discovery of "seeing the familiar." Worldwide, the cycle of leaves growing and falling continues tooccur. This research will help us to find relationships between species of the past andpresent.
III. Materials
· Nets
· Yellow Stakes
· Trash Bags
· Electric Scale
· Glass Jar
· Food Coloring
· Water
· Plastic Pieces
· Western Leaves
· Yard Stick
IV. Methods
The fundamental method in which we researched our problem was through the useof leaf collection and biomassing. We constructed several large "leaf traps" under three trees surrounding Boyd Hall. We have selected one Bur Oak, one Black Oak, and one Ginkgo Biloba. We constructed our "leaf traps" by securing large nets with stakes around the base of our subject trees. The collection of our leaves took place every Tuesday and Thursday morning. We placed the leaves in large trash bags each collection day, so that they could dry out before we biomassed them. The leaf collection period took place October 14-December 2. After the leaves had fallen off our trees, we began to sort out the leaves in the trash bags. This was a very tedious procedure because we had several bags for many of the days. We weighed the leaves in the bags to figure out the total mass that fell over the time periods between collection. Through use of an electric scale, we were able to achieve accurate biomasses. We recorded our data in charts for analysis. We acknowledge there were several variables which affected the accuracy in our results. One of our biggest concerns was that some leaves had fallen off the trees prior to our collection period. It would be nearly impossible to collect all of the leaves that fall off our three trees. The leaves which were trapped by the nets were only representative of the rate which the tree's leaves fell. It would have been very difficult to create nets large enough to surround the entire bases of the observed trees. Even if it was possible to find nets large enough, it would have been nearly impossible to collect all of the leaves from them every other day. Weather also played a major role in our experiment. Wind and rainfall affected the rate and placement of leaf fall-rate. Hopefully, passing students did not tamper with our experiment. We know that it was very tempting for them to play with our nets, so we will have to take this into careful consideration. We strategically placed signs and markers which allowed the nets to be visible as pedestrians neared our observation sites. In order to incorporate our class in our lab, we performed a demonstration showing examples of leaf trajectory model. The class was required to read the information provided in our lab packet. We dropped slips of plastic cut in different shapes into a large cylindrical container filled with water. Food coloring was smeared onto the plastic to show the trajectory of the path. Students successfully determined whether the pieces of plastic fluttered or tumbled. During the second part of the lab, students collected leaves inthe forest outside of Boyd Hall. They were divided into their lab groups and were lead outside into the forest. Students measured ¼ of a square meter on the forest ground and collected all of these leaves into plastic bags. Students returned to the classroom and used the provided handouts to identify the leaves. All of the different observations that helped them to identify the classification of the leaves were recorded on the data sheet provided. We used Stat View to analyze all of our sets of data. We used histograms, regressions, t-tests, and the Bivariate Line Chart to display are statistics.
V. Data Sheet
Our data sheet can be found in Westernís Open Access. Our files are titled "Leaf Drop" and "Leaf Drop View."
VI. Results
Our statistical tests and charts can be found in the open access file on the computers in the Peer Science Center as well. ("Leaf Drop" and "Leaf Drop View" ) During the process of leaf collection, we were able to make several observations concerning the study. There were definitely distinct patterns in the leaf fall cycle between our three trees. We were able to notice these patterns through the amounts of leaves we collected every Tuesday and Thursday. The Black Oak continuously dropped its leaves throughout our collection process, yet it did prove to show a peak of leaf fall towards the end of observation. The Bur Oak held onto its leaves for a longer period of time, but showed a peak in the amount of leaf fall as well. The Ginkgo Biloba was the most interesting of the three species because it held onto its leaves, shedding them quickly over the coarse of one week. All of these observation were made as we collected the leaves in trash bags. After biomassing the trash bags and recording our data into charts, we were able to scientifically analyze our data through the use of Stat View. The first method of analysis we used was to make a histogram for each set of data. The histograms were unsuccessful in providing information towards proving our hypothesis. They did accurately show the distribution of leaf fall for each tree. The t-test created from the histograms proved to be useless as well. The p-values which were found by this test were insignificant. The p-values were all well over .05 with the closet value being the BlackOak verses the Gingko Bibloba with a percentage of .1872. The next method we used for statistical analysis was the ANOVA tables. This allowed us to test the regressions within our results. The regressions assisted us in finding the statistics which would later support our hypothesis. Three p-values were solved through comparisons between each of the species of trees. The first comparison was the Gingko Biloba verses the Black Oak. This comparison gave us a p-value of .0009 which allowed us to reject the null hypothesis. This means that there was a significant difference between the Black Oak's leaf drop cycle and the Gingko Biloba. The second comparison was between the Gingko Biloba and the Bur Oak. This provided for the most fascinating results. The p-value found between these two species was .9589 which did not reject the null hypothesis. This showed that the two tree's leaf drop patterns were similar. The final comparison was between the two Oak trees. The result of this comparison was given as a p-value of .4020. This values hows that the null hypothesis will not be rejected. There was no significant difference between data found for both trees. From all of these regressions, we were able to prove that the Gingko Biloba did drop it's leaf at a significantly different rate than the other trees. Our concluding presentation of statistical data was through the Bivariate Line Chart. This proved to be our most useful tool in confirming our hypothesis. It clearly showed the peak in the Gingko Biloba's leaf fall cycle. The only discrepancy concerning this graph was that the dates listed on the x-axis were inadvertently converted by thebcomputer. This had no effect on the lines displaying data but can be quite confusing to the untrained eye.
VII. Discussion
There were many different aspects of the Miami Leaf Drop lab which leave a great amount of room for discussion. This project's accuracy was dependent on many uncontrollable variables. The fundamental structure of our experiment was really quite efficient. There were many conditions which occurred throughout the collection period that we had not accounted for. One of the greatest effects on our data came from the weather. We were unable to estimate how much the weather effects the rate of leaf drop.We were only able to record the weather for each collection period to provide along withour data. In future studies on leaf drop patterns, measurement of the weather's effect might provide a greater accuracy in the data. Below is the chart of the weather conditions which occurred during our leaf collection;
Table 1: Weather conditions which occurred during leaf collection
10-14-99 55°F cloudy
10-19-99 40°F rain,mist
10-21-99 30°F mist
10-26-99 45°F clear
10-28-99 45°F cloudy
11-02-99 55°F rain
11-04-99 50°F mist
11-09-99 40°F mist, fog
11-11-99 45°F cloudy
11-16-99 45°F cloudy
11-18-99 32°F partly cloudy
11-30-99 21°F clear
12-02-99 30°F cloudy
There were several other variables which influenced the accuracy of our lab. The leaf blowers blew all of the leaves out of the nets under the Black Oak on December 2. This made the biomassing incorrect for that day. Students and animals might also have tampered with our nets. For future studies funded with a higher budget, the nets could surround the entire tree. This would capture all of the leaves which fell from the branches. Our lab only accounted for the leaves which were trapped by the nets found on the ground. This only gave us a percentage of leaves verses the entire collection.
VII. Conclusion
In conclusion, we feel that the Miami Leaf Drop was quite a success! Our careful collection and recording techniques provided for an outstanding discovery of results. We manage to set up the proper method of testing the leaf fall patterns between the three different species of trees. In a more general sense, we proved our hypothesis to be correct. Though the Gingko Biloba did not drop its leaves overnight, it did drop its leaves over the course of one week. This was a much more accelerated rate compared to the other species of Oak trees. We are proud of our dedication and time put into this study! Through this lab we have learned the proper methods in establishing experiments and the techniques used to analyze the results. We also became more acclimated with StatView and the numerous ways it can manipulate data. Most importantly, we learned to be patient with science and the world around us! Over all, this lab was a wonderful learning experience!
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