We studied Earth System Science at the Indiana School for the Deaf (ISD) and at the Model Secondary School for the Deaf (MSSD). We learned about the Earth system and how connections happen between all the spheres. We studied about the problems with carbon dioxide, and the flow of energy through the Earth system. We wanted to know if global warming is happening, and if it influences the changing of colors of leaves in autumn. We wondered if these things are connected.

We learned about Green Down, and that it is an example of a phenological cycle. Phenology is the study of how living organisms respond to seasonal and climatic changes in their environment. We learned that the timing of leaf fall in autumn is influenced by temperature, and that leaf fall can be used to study regional and global vegetation patterns, the changes which occur from year to year, and plants' responses to climate change. This is the first year we studied autumn leaves at our schools, and some questions can only be answered over the course of several years with a lot of data. We decided to start collecting data about what happens to the leaves at our schools during autumn. ISD researched Sugar Maple leaves, while MSSD collected data on Silver Maple leaves, which are similar species. We wanted to compare how the environment in two different areas influences the colors of the leaves.

Therefore our research question is how does the environment change and how do leaves change during the autumn season, and does the same thing happen at both of our schools?

Background Information

A leaf has three kinds of pigment: chlorophyll, carotenoids, and anthocyanins. Chlorophyll, the green pigment, is necessary for photosynthesis, which produces sugars within the leaf. Carotenoids are the yellow, orange, and brown colors you see in corn, bananas, and buttercups. Carotenoids are always present in leaves, but are masked by the green of chlorophyll during much of the year. Anthocyanins give red colors to plants such as raspberries and strawberries. Throughout the growing season, the chlorophyll and carotenoids are present in the leaf cells. During autumn, bright light and an excess of sugar produced by the leaf makes anthocyanins appear. The drawing below shows the parts of a leaf and how the structures and cells are arranged inside.

(Picture from p. 647, Biology, The Dynamics of Life, Glencoe/McGraw-Hill 1998)

The top layer of a leaf is called the cuticle. A GLOBE scientist taught us that the cuticle is important to how certain wavelengths are reflected. For example, the thicker the cuticle, the greater the % reflectance in the blue wavelengths. The cuticle has no effect on reflectance of the red wavelengths. The thickness of the cuticle does affect the green wavelengths. We did not attempt to observe changes in the cuticle in this investigation, but cuticle changes might explain some of the results we got.

Hypothesis

In this investigation we tested the hypothesis that reflectance of red, crimson, and orange wavelengths from a leaf's surface would increase, reflectance of the blue wavelength would stay about the same, and reflectance of the green wavelength would decrease as the fall season progresses and the environment changes. We expected red, crimson, and orange wavelengths to increase over the fall season as the temperatures decreased, because we read about how cold temperatures produce the brightest fall colors and about how the trees produce anthocyanins in the fall. We expected the blue wavelengths to stay about the same because the leaf seems to absorb the blue in the upper layers. We expected the green wavelength to decrease because we know that the chlorophyll is broken down and pulled back into the tree for storage during the coldest months. We expected the yellow wavelength to be unchanging, since carotenoids are always present in the leaf, and when chlorophyll breaks down the yellows may appear.