Seed Structure and Dispersal in Acer
saccharum (Sugar Maple)
The purpose of this lab is to find out if variations in Acer saccharum (sugar maple) seed structure and flight behavior affect their dispersal. Sipe and Linnerooth (1995) conduct an experiment involving samara morphology and flight behavior in silver maples. Their findings showed a wide variety in seed structure and behavior existed within the silver maple population. This experiment in conjunction with the findings of Greene and Johnson (1991) relating mass and terminal velocity, formed the basis of our hypothesis. We believe that despite intraspecific variations in seed structure and terminal velocity of
flight among different Acer saccharum subspecies, each seed uniquely maximizes its dispersal potential.
This lab idea has gone through many revisions. It has been narrowed down from general seed dispersal to concentrating on one prominent tree species in the area. We chose the maple tree for their accessible and easily identifiable seeds. The two joined seeds are commonly known as "helicopters" for their wings that propel them into a spiraling motion. Samara is the scientific term for the entire seed structure.
From reading the integrated experiments of Sipe and Linnerooth (1995), Greene and Johnson (1991) and (1992), Guries and Nordheim (1984), and Peroni (1994), we found supportive evidence for our experiment with the Acer saccharum. The topic is a pertinent one as the evolution of seed variation is still debated among scientists as Greene and Johnson (1992). The maple seed structure undoubtedly vary, but why? Did adaptive features evolve? For example, the samara blade length decreased over time in order for the seed to enter autorotation sooner to maximize its dispersal distance. Or are these
variations hereditary? The objective of this experiment is show that each seed variation provides optimal dispersal.
Our specific questions incorporate seed dispersal variables such as the structure and weight of the seed, the velocity of the wind affecting the distance that the seed is carried, the initial falling distance prior to autorotation and terminal velocity of the seed. By collecting the seeds from under the tree at various locations (utilize a random sampling strategy) and reenacting the moment of seed release, we hope to prove whether or not our hypothesis is correct and coincides with the studies of our predessors.
Relevance of your research question:
While researching our topic we found a previous Miami University group study with a completed project similar to our own in addition to the studies found in scientific journals. This shows that this issue of maple seed structure, velocity and dispersal is a prominent topic not only in the scientific community but also on our campus.
Through previous research already stated, it was also discovered that the maple population is diminishing. Studying the tree’s mechanism of reproduction (the seed) could provide clues as to why this is happening. The maple tree produces an abundance of the seeds to increase the chance of reproduction, but is this enough? Does the maple tree need to adapt its seeds according to its surroundings in order to maximize this chance? We maintain that it does. Through our experiment we hope to discover which structural designs are most advantageous. The maple tree is an example of
how adaptive features in nature attempt to ensure reproductive success, therefore ensuring the survival of the species. In the article by Sipe and Linnerooth (1995), they say that "a significant role in population persistence, and that natural selection can work within a species to shape fruit morphologies that enhance dispersal potential." This implies that maple trees along with other species do in fact alter certain characteristics that prove advantageous to prolonging their species.
Materials and Methods:
To carry out this experiment we will need a fan, a permanent marker, a large white cloth, tape measure, 10-foot ladder, electronic scales, a stopwatch, and numerous samples of seeds from four different sugar maple trees.
The first part of our experiment will be to observe the samara design of each of the tested trees. The weight of the seeds, the angle between the two wings, the length of the wingspan, and wing shape, will be compared and contrasted to each other. The wing shape will be classified using the diagram with various shapes from the article by Sipes and Linnerooth (1991). Determine the weight of the samaras
to the .01mg using the electronic scale.
The second part of our experiment is to test the distance that the seed falls from the trunk of the tree. A white sheet will be placed beneath the tree, spanning from the trunk of the tree outward to approximately 20 feet past the furthest branch. The seed dispersal will be monitored daily for one week. At the end of the week, the number of seeds on the sheet will be counted in increments of 5 feet from the trunk of the tree. This experiment will be repeated for each of the four trees.
The third component of our experiment will be to calculate the terminal velocity of the samaras. We will measure the distance that the seed falls by dropping the seed from a predetermined height then we will measure how long it takes the seed to fall using the stopwatch. We will factor this time into the terminal velocity equation. We will repeat this five times for each of the four seed samples.
The fourth component of the experiment is a simulation of the seed dispersal due to wind. In preparation, the seeds will need to be dried in a microwave (set on low; time yet to be determined) to remove excess water. We do this based on the assumption that the tree releases the seed when most of the water is removed. The seed will be suspended from a fixed point ten feet above the ground. The fan will be placed on the ladder at this height as well. Turn the fan on to it's medium setting (this will represent an average wind current which is a minimum of 1m/s and a maximum of 4m/s for abscission according to Greene and Johnson's 1991 study). The seed will be released and carried by the wind current. Measure the displacement of the dropped seed from the midpoint of the base of the ladder and record. The velocity of the wind (the fan's current) will be determined by using the dispersal distance equation as follows:
Dispersal distance (m)= wind velocity(m/s) X (height of release (m) - initial fall distance)/
Repeat five times for each seed, from each of the four trees.
We believe our design is significantly sound because we incorporate a field study as well as a model. The two tests decrease data discrepancies (human error) by supporting one another. We researched the Internet, proposed our idea to our peers, and consulted faculty for further experimental design assistance. A large sampling pool will ensure unbiased results.
Class participation is as follows: The class will be divided into four groups led by one of the four experimenters. Each leader will take their group to one of the four sugar maple trees. Under the leader's supervision they will be asked to collect a random sampling of the fallen samaras which from the white sheet that had been laid down a week prior. The class will be asked to observe and record the various components of seed structure; wing length, span, shape, and the angle between the wings. They will classify the wing shape based on the drawings that they have been furnished with.
Equipped with this newfound knowledge they can deduce which seed design is most advantageous for dispersal. They will next be asked to perform the simulated seed dispersal experiment.
A data sheet with three tables have been supplemented; one for each component of the experiment.
Our experiment will require approximately a week and a half to carry out and may be repeated to increase research accuracy.
Results (Methods for Interpretation):
Utilizing the Stat View program a t-test will be conducted between the simulation and the actual observation portion of the experiment. The p-value that will be obtained will determine whether the differences in the results are likely due to chance alone (not significantly different). If the p-value is greater than .05 we will conclude that the differences in the results are not statistically significant. If the p-value is less than .05 then the differences in the results are statistically significant. We will also use histograms to chart the frequency of the seed counts.
Our results will be displayed in our data table and graphs will be determined based upon our results.
Discussion and Conclusion:
Based upon the studies of our predecessors and our expected results, we predict that there is no one samara structure that is advantageous over the others. Our conclusion is that each individual maple tree possesses uniquely designed seeds, enabling maximum dispersal, thereby perpetuating its species. There is no one dominant seed variant that more efficiently disperses seeds. Collectively, all the seed designs balance out one another due to their combinations of features. The yet to be determined terminal velocities and flight distances will found the basis of our evidence for this. Terminal velocities among the species are expected to be relatively similar based on the findings of Guries and Nordheim (1984). If so, a heavier seed will be equipped with longer blade lengths and the lighter seeds will have shorter blade lengths to ensure equal velocities.
After we have analyzed our result we expect that we will be faced with additional questions having to with seed dispersal. If we were to investigate this topic further we could also include the various heights of the seeds on the differing maple trees.
Sugar Maple seed production and dissemination.
Maple tree seed dispersal and seed trapping
3.Annual Review of Ecology and Systematic, Vol. 25 (1994) pp.263-292
A Day in the Life of a Seed: Movements and Fates of Seeds and their implications for
natural and managed systems
4. Snipe, Timothy W. and Amy R. Linnerooth. American Journal of Botany. Intraspecific variation in samara morphology and flight behavior in Acer Saccharinum. Baltimore. Vol.82 (1995) pp.1412-1419.
5. Peroni, Patricia A. American Journal of Botany. Seed Size and Sispersal Potential of Acer Rubrum (Aceraceae) Samaras Produced by Populations in Early and Late Successional Environments. Durham. Vol. 81 (1994) pp. 1428-1434.
6. Greene, D. F. and E. A. Johnson. Fruit absicission in Acer saccharinum with reference to seed dispersal. Montreal. 1992.
7. ---. The American Nationalist: Can the Variation in Samara Mass and Terminal Velocity on an Individual Plant Affect the Distribution of Dispersal Distances. Vol.139, No. 4. Calgary.
8. Guries, Raymond P. and Erik V. Nordheim. Flight Characteristics and Dispersal Potential of Maple Samaras. Vol. 30, No. 2 (1984).
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