Light Reflectance from Sugar Maple Leaves


Questions to Investigate

1. What happens to leaves in the fall? Why do leaves change color?

2. How long does it take for leaves to change color?

3. How does light reflectance change as leaves change color?



1. Some color would have less light reflectance (green and blue).

2. Some colors would have more reflectance (red, orange, and amber).

3. Fewer hours of sunlight and colder temperatures will cause leaves to reflect less green light.



*Anatomy of a leaf


* Why scientists think leaves change color?
In the past, scientists thought the cold and fewer hours of sunlight affected
the chlorophyll (a green substance that makes leaves look green). The trees stop
making chlorophyll in the fall, and the other colors show up. But now, scientists are
still studying this, looking for more information. They are trying to find out how
the weather affects the changing of leaves' colors.

(On my graph, you will notice the reflectance of green stays the
same while other colors increase or decrease.)


Equipment and Materials
We used clipboard, white and black papers, the ALTA,
graphs to record information, pencils, and computers!

We picked two leaves that we will use for the rest of the season. We recorded
data for control and then started the first list of ALTA reflectance on black paper.
That was on October 11th and we went back to the tree around two times per week
and measure the reflectance using the ALTA. We put the information on Excel and we
made graphs for each color, and we measured the average, and figured out the
percentage for each. I have several graphs about this below.




ALTA Reflectance Data and Graphs:


Weather Data and Graphs


Results and Conclusions

Blue reflectance really did not change very much, with a slight fluctuation of +1%.
Green showed about a 14% increase in reflectance.
Yellow showed about a 13% increase in reflectance.
Amber showed about a 7% increase.
Orange showed about a 9% increase.
Crimson showed about a 21% increase.
Red showed an increase of 16%.
IR-1 reflectance had huge increases at the end of the study of 34%.
IR-2 varied somewhat with an 8% increase in reflectance.

All of the colors showed a slight dip in the first few measurements. This
could have been caused by differences in the weather, cloud cover, or by our
"learning curve" in using the ALTA reflectance spectrometer.


Weather prior to the reflectance study was very dry. During the study, small
amounts of rain (.4 mm and 1.2 mm) occured on October 16 and October 31.

Large amounts of rain (12 and 13.3 mm) were recorded on October 21 and October 29.

Increases in rain seemed to correspond to increases in IR reflectance measurements.


Average temperature varied during the study, with a decrease of
6 degree Celsius. Highest average temperature was 10.45 on October 23.
Lowest average temperature was 2.3 on November 2.


Biology, the Dynamics of Life, Glencoe/McGraw-Hill, pages 646-647


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