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Maple Samara Design and Dispersal

Introduction:

Plants have yet to evolve powered flight, but the seeds of various trees have

developed a technique of gliding (Alexander, 2002). In order for seeds to “glide” some

sort of wing or lifting surface must be attached to the leaf (Alexander, 2002). Winged

seeds are called samaras (Alexander, 2002). Samara refers to the whole structure,

consisting of the seed, which contains the plant embryo, and the aerodynamic wing

surface (Alexander, 2002). The majority of samaras are the autogyrating type, which

include the seeds of maple, pine, ash, and tulip poplar trees (Alexander, 2002). These

move in a “helicopter” fashion (Alexander, 2002). These samaras are comprised of the

wing and seed, in which the seed is located at one tip (Alexander, 2002). The center of

gravity of these samaras is located at or near the seed mass (Alexander, 2002). When

autogyrating samaras fall to the ground with the seed end downward, the winged end

begins to rotate around the seed, creating flight (Alexander, 2002).

The ecological roles, and habitats of many maple species have influenced the

evolution of the shape and design of their samaras. These alterations are specific to the

dispersal needs of each species. Examples of these differences can be seen in Acer

pensylvanicum (Striped Maple), Acer spicatum (Mountain Maple), Acer campestris

(Hedge Maple), Acer platanoides (Norway Maple), Acer tartarica (Amur Maple). Acer

pensylvanicum is an understory tree, and is the most-shade tolerant of deciduous trees

(Wikipedia, 2010). The samara of other species are designed to travel away from the

understory of the parent in order to receive optimal sunlight (Alexander, 2002).

Although, it is possible, that the Striped Maple samara may not be dependent on this

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flight factor, due to its shade tolerance. Acer Spicatum is a small deciduous shrub or tree,

which is known to be located near streams (Wikipedia, 2010). This habitat is extremely

useful for the distribution of its seeds via samara dispersal. Acer campestris is an

intermediate species in the ecological succession of disturbed areas (Wikipedia, 2010).

Hedge Maple has high light requirements during its seed-bearing years (Wikipedia,

2010). In order for Hedge Maple seed to germinate and survive, it is possible that the

samara is designed to carry the seed to a non-shaded area. Acer platanoides are known to

not be long-lived, so because of this, the species typically produces a large quantity of

viable seeds (Wikipedia, 2010). It is plausible that the Norway Maple’s samaras are

designed to evenly disperse from one another, because of its large production of seeds.

Acer tartarica is known to be an invasive species that is a secondary successive species,

so it has the potential to be outcompeted by tertiary successive species (Wikipedia, 2010).

To prevent this, Amur Maple species produce abundant seeds, ultimately producing high

amounts of samaras.

This experiment was comprised of two main objectives. The first objective was to

compare samara wing loading (grams/mm2) and descent time of different maple species.

The natural history of each five maple species was examined, and predictions dependent

on wing loading and dispersal potential for each species were made. It was hypothesized

that there is a difference in samara decent time and wing loading among Maple species.

The second objective of this experiment examined the effect altering the curvature, of

Acer platanoides’ samara to a straightened edge, would have on its descent time. It was

hypothesized that decent time of the samaras with the straightened edge would be lower

than the samara with a curved edge.

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Materials and Methods:

Forty samaras per species (Acer pensylvanicum, Acer spicatum, Acer campestris,

Acer platanoides, Acer tartarica, were collected. The wing mass (grams) and area for

each of these 40 samaras per species was recorded. The wing area was determined by

using MVH Image analysis software. Wing loading (grams/mm2) was then calculated by

dividing the mass by the area. Next, forty samaras per species were individually dropped

from 7.6 m in a deserted hallway. The descent time of each samara was recorded using a

stopwatch. An Analysis of Variance test (ANOVA) was run to examine differences in

wing-loading and descent time for the five maple species. Next, a scatter plot for each

species was created that compared the effects of Wing Loading on Descent Time. A

regression analysis was then used to find the regression equation for the relationship

between Wing Loading and Descent Time.

For the further study, the effect of altering the curvature of the Acer platanoides’

samara, to a straight line, on descent time was examined. The control group consisted of

unaltered Acer platanoides’ samaras. Each control samara’s mass, wing loading and

descent time, and statistical analysis were all used from the same procedures used in the

above description. For the experimental group a precise cut was made to each of the forty

samaras. A cut was made, using a razor blade, right where the seed’s bottom end met the

bottom side of the samara wing to the edge of the samara. This cut removed the curvature

at the bottom of the samara wing, altering it to a straight edge. For the experimental

group, the mass, wing loading, and descent time, and statistical analysis were all used

from the same procedures as described above.

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Results:

Part I.

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Table 1. Descent Time and Wing Loading Values of the Five Maple Species

A. spicatum A. pensylvanicum A. campestris A. platanoides A. tartarica

Descent Time

Mean 9.32225 7.81075 6.104 7.5455 9.72275

S.D. 1.74429 1.38359 0.76145 1.69138 1.88498

C.V. 18.7111 17.714 12.4745 22.4157 19.3873

Wing Loading

Mean 0.194 0.307 0.288 0.257 0.169

S.D. 0.075 0.094 0.062 0.091 0.039

C.V. 38.532 30.709 21.511 35.522 23.175

Table 2. ANOVA Test Based Upon Descent Time of the Five Maple Species

Source of Variation SS df MS F P-value F crit

Between Groups 340.094357 4

85.02358925

35.57294336

2.645E-22

2.417962542

Within Groups 466.073322

5 195 2.39011960

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Total 806.167679

5 199

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Table 3. ANOVA Test Based Upon Wing Loading of the Five Maple Species

Source of Variation SS df MS F P-value F crit

Between Groups 0.511568 4 0.127892 21.95535 8.97E-15 2.421843

Within Groups 1.048517 180 0.005825

Total 1.560085 184

According to Figure 1. as the wing loading of Acer spicatum increased, the decent

time decreased. As shown in Table 1. the Acer spicatum had the second highest descent

time of the five maple species. The coefficient of variance were fairly low meaning that

there was not much variation in descent time from the mean. Although, as shown in

Table 1, the Acer spicatum samaras’ mean wing loading was the second lowest of the five

maple species. According to Table 1, the standard deviation was fairly low, which

indicated that there is not much wing-loading variation in this species.

According to Figure 2. as the wing loading of Acer pensylcanicum increased, the

descent time increased. As shown in Table 1. the Acer pensylcanicum had the third

highest descent time of the five maple species. Although, as shown in Table 1, the Acer

pensylcanicum samaras’ mean wing loading was the highest of the five maple species.

According to Table 1, the standard deviation was the highest of the five maple species,

which indicated that the samaras of this species’ wing loading varies the most of the five

species.

According to Figure 3. as the wing loading of Acer campestris increased, the

descent time decreased. As shown in Table 1. the Acer campestris had the lowest descent

time of the five maple species. Both its standard deviation and coefficient of variance

were fairly low meaning that there was not much variation in descent time from the

mean. Although, as shown in Table 1, the Acer campestris samaras’ mean wing loading

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was the second highest of the five maple species.

According to Figure 4. as the wing loading of Acer platanoides increased, the

descent time decreased. As shown in Table 1. the Acer platanoides had the second lowest

descent time of the five maple species. Although, as shown in Table 1, the Acer

platanoides samaras’ mean wing loading was the third highest of the five maple species.

According to Figure 5. as the wing loading of Acer tartarica increased, the decent

time increased. As shown in Table 1. the Acer tartarica had the highest descent time of

the five maple species. Although, as shown in Table 1, the Acer tartarica samaras’ mean

wing loading was the lowest of the five maple species. According to Table 1, the standard

deviation was the lowest of the five maple species, which indicated that there is not much

wing-loading variation in this species.

According to Table 2, the descent time P-value (2.645E-22) is less than .05 and

the descent time F value (35.57294336) is higher than the F critical (2.417962542). This

relationship indicates that descent time is significant among the five Maple species.

According to Table 3, the wing loading P-value (8.97E-15) is less than .05 and the

descent time F value (21.95535) is higher than the F critical (2.421843). This relationship

indicates that wing loading is significant among the five Maple species.

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Table 4. Comparison of Control Descent Time and Experimental Descent

Control Descent Time

Mean 7.5455

Standard Error 0.267430545

Median 7.565

Mode 6.27

Standard Deviation 1.691379273

Sample Variance 2.860763846

Kurtosis -0.478925054

Skewness -0.192141731

Range 7.1

Minimum 3.7

Maximum 10.8

Sum 301.82

Count 40

Experimental Descent Time

Mean 6.85675

Standard Error 0.215534335

Median 6.755

Mode 7.47

Standard Deviation 1.363158827

Sample Variance 1.858201987

Kurtosis -0.312951259

Skewness 0.417342616

Range 5.45

Minimum 4.62

Maximum 10.07

Sum 274.27

Count 40

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Table 5. ANOVA Test Based Upon Descent Time of Acer Platanoides

ANOVA

Source of

Variation SS df MS F P-value F crit

Between

Groups 9.48753125 1 9.48753125 4.021021378 0.048405272 3.963471921

Within

Groups 184.0396675 78 2.359482917

Total 193.5271988 79

Table 6. ANOVA Test Based Upon Wing Loading of Acer Platanoides

Source of

Variation SS df MS F P-value F crit

Between Groups

2.10037E-

09 1

2.10037E-

09 0.228055235 0.634305118 3.963472051

Within Groups

7.18374E-

07 78

9.20992E-

09

Total

7.20474E-

07 79

According to Figure 6 as wing loading of Acer platanoides increased descent time

decreased. This relationship is more significant in the control group of Acer platanoides,

which is shown in Figure 4. Table 4 compares the descent time of the control and

experimental groups. The mean descent time of the experimental group, Acer platanoides

samaras with a straight edged bottom, (6.8567 seconds) was less than the control group

(7.5455 seconds).

As shown in Table 5, the descent time P-value is .0484, and the F-value (4.02102)

is greater than the F-critical (3.9634). These values indicate that a significant difference

between the control and the experimental descent times exists.

As shown in Table 6, the wing loading P-value is 0.634305118, and the F-value

(2.10037E-09) is not greater than the F-critical (3.963472051). These values indicate that

a significant difference between the control and the experimental wing loading values

does not exist.

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Discussion:

For the first objective of this experiment it was hypothesized that there is a

significant difference in samara decent time and wing loading among Maple species.

Through data collection and statistical analysis, specifically using ANOVA, our results

indicated that descent time and wing loading is significant among the five Maple species.

As previously mentioned Acer spicatum (Mountain Maple), Acer campestris (Hedge

Maple), Acer platanoides (Norway Maple), Acer tartarica (Amur Maple) all have

varying habitats and ecological characteristics. As explained by Nathan and Schiller

(1996) samara morphology, and a wide variety of dispersal devices that enhance dispersal

have evolved. This inter-specific variation between samaras has been dependent on the

ability for greater dispersal variability (Nathan and Schiller 1996). For example, wind-

dispersed plants adapt to traits that affect the height of seed release, seed abscission

probability and aerodynamic properties (Nathan and Schiller, 1996). Our results support

the idea that there is much inter-specific samara variation due to the various habitats and

ecological characteristics of these different Maple species.

For the second objective of this experiment it was hypothesized that descent time

of the Acer platanoides samaras with the straightened edge would be lower than the

samara with a curved edge. Through data collection and statistical analysis, specifically

using ANOVA, our results indicated that the mean descent time of the experimental

group (samaras with straightened edges) was lower than the mean descent time of the

control group (untouched samaras). Our ANOVA results indicated that that a significant

difference between the control and the experimental descent times exists, but a significant

difference between the control and the wing loading does not exist. These results were

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also found by Sipe and Linnerooth (1995). The descent time of the long-straight and

dwarf samaras, both with straight edge bottoms, were lower than the descent times of

Angel wing and boomerang samaras, which have a curved edge (Sipe and Linnerooth

1995). The Acer platanoides’ samara have evolved a curved-edge in order to increase its

lift-time, ultimately traveling further from the parents, and increasing dispersal. Dispersal

behavior plays a significant role in the survival of maple populations, in which alter

samara morphology to increase dispersal potential (Sipe and Linnerooth, 1995).

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Works Cited

Acer campestris. Accessed 11/26/10 from: http://en.wikipedia.org/wiki/Hedge_Maple

Acer pensylvanicum. Accessed 11/26/10 from:

http://en.wikipedia.org/wiki/Striped_maple

Acer platanoides. Accessed 11/26/10 from: http://en.wikipedia.org/wiki/Norway_maple

Acer spicatum. Accessed 11/26/10 from: http://en.wikipedia.org/wiki/Mountain_maple

Acer tartarica. Accessed 11/26/10 from: http://en.wikipedia.org/wiki/Amur_maple

Alexander, D. 2002. Natural Flyers: birds, insects, and the biomechanics of flight. The

John Hopkins University Press. 49-57.

Nathan, R., Schiller, R. 1996. Samaras Aerodynamic Properties in Pinus Halepensis

Mill., a colonizing tree species, remain constant despite considerable variation in

morphology. Preservation of Our World in the Wake of Change. Vol. VI A/B

Sipe, T., Linnerooth, A. 1995. Intraspecific Variation In Samara Morphology and Flight

Behavior in Acer Saccharinum. American Journal of Biology. 82(11): 1412-1419.