Global Patterns in Green Up and Green DownDirections
1. Read through this handout, then print out the four worksheets.
2. Look carefully at the color visualizations of January and July vegetation vigor, and Global land cover. You can also refer to the Natural Vegetation figure in Goodes World Atlas (pages 24 & 25 in the 21st edition, pages 42-3 in 22nd edition).
3. Cut out and assemble the flip books by cutting out each month, the assembling the months in order
4. Fill in the worksheets.
5. Visit the vegetation locations listed below at www.confluence.org
6. Answer the questions at the bottom of this sheet and turn in only the answers to these questions.
Key Concepts
• The Normalized Difference Vegetation Index (NDVI) measures vegetation vigor. NDVI is calculated from satellite data, thus allowing global coverage.
• Vegetation growth and decline follows the seasonal cycle with an annual “green up” in the spring and summer and a “green down” (or senescence) in the fall and winter. The cycle of greenup and greendown occurs within ecosystems at all scales. Large-scale regional land covers show characteristic patterns that identify them (e.g., rain forests nearly uniformly high, deserts nearly uniformly low, tundra has a rapid rise that lasts only a short time, etc.).
Background
Everyone experiences local changes in vegetation that occur in fall and spring. This activity is designed to connect your local experiences of seasonal change in vegetation with global patterns of change. These global patterns in vegetation growth and decline or in “plant waves of green up and green down” follow the annual climate cycle. As a result, what occurs in the Northern and Southern Hemispheres is roughly reversed. Just as summer in the Northern Hemisphere occurs during winter in the Southern Hemisphere, so Green-Up occurs in the North while Green-Down occurs in the South.
This activity focuses on visualizations of vegetation vigor that were collected by satellites. We have global coverage because the data was collected by satellite. The measure of vegetation vigor is made in terms of a calculated quantity called Normalized Difference Vegetation Index. NDVI provides a measure of how much sunlight is being used by plants for photosynthesis. These values are unitless, since NDVI is calculated as a ratio of absorbed light in the red wavelengths and reflected light in the near infrared wavelengths. While the measurement does not provide a precise measure of vegetation and is subject to several issues that compromise its consistency, it is very useful.
There are three visualizations used in this activity. The initial two illustrate the seasonal extremes of vegetation vigor by showing vegetation vigor during January and July (Figure 1). The other one helps to explain the observed seasonal change by showing the type of vegetation and land cover present.
Seasonal Extremes in January and July
The visualizations of vegetation vigor are drawn using shades of green (dark values are higher) In the vegetation vigor visualization, darker shades of green are used to represent greater amounts of growing vegetation and lighter shades used for less actively growing vegetation. Primary patterns shown in the January and July visualizations of vegetation vigor. In January most of the high values are found in the Southern Hemisphere (particularly in Central America, South America, Africa, and South Asia).
Now look at the vegetation vigor in July. In July, much of the mid-latitudes of the Northern Hemisphere show substantial vigor, especially in the eastern part of North America and in Europe and Asia. Further, there remains substantial vegetation vigor in the Southern Hemisphere (in South America, Africa, and South Asia) in a similar pattern, but in reduced amounts, as in January. From the visualizations, it can be seen that July has much higher values overall because there is substantial vigor in both hemispheres. You can quantify how much higher July is than January using the global means. These means show approximately a fifty percent rise: from 0.16 in January to 0.29 in July.
But why is the Northern Hemisphere’s summer so much more productive globally than the Southern Hemisphere’s summer? One important part of the answer is that the Northern Hemisphere experiences a sharper seasonal change than the Southern, since most of the Earth’s land is located in the North and land is more easily heated and cooled than are oceans.
However, another part of the answer lies in their distinctive landcovers, for example, the rain forests of the Southern Hemispheres stay green all year.
Land cover visualization
Many of your questions about why individual areas are high or low can be answered by looking at the land cover visualization below. For example, compare the rain forests of South America (the broadleaf evergreen class that is blue-green) and the Saharan desert in Africa (a desert and scrubland class that is tan). The rain forests show high values (bright green) year round while the desert shows low values (pale yellow) year round. Overall, the difference can be explained by the type of ecosystem that occurs there, however, many ecosystems are not constant across the year but change greatly.
Check your comprehension
Answers at the bottom of the page
1. What does the color dark green indicate?
2. What does the color light green indicate?
3. What patterns do you notice between landcover as it is classified in Figure 2 and the regions that are dark green in both January and July (Figure 1)? What about the regions that are light green in both January and July?
4. Which hemisphere has a stronger vegetation vigor in January? Which hemisphere has a stronger vegetation vigor in July?
Worksheets
1.Print out the four worksheets. They are below these instructions, and called “flipbook 1”, “flipbook 2”, “worksheet 1”, and “worksheet 2”. You will need Adobe Acrobat to read the worksheets. Adobe Acrobat is a FREE software program.
2. Cut out the pages of the flipbook and assemble it in order.
3. Use the flipbook to help characterize the seasonal cycles for each land cover type on the worksheets. The 5 landcover types that we are looking at are located on the map in worksheet 2. Your job is to match the lines on the graph in worksheet #2 to the landcover types and locations shown on the worksheet 2 map. The graph reflects the NDVI values as shown in the flipbook (worksheets 3&4). So for example, follow the NDVI value for broadleaf evergreen (the northern part of South America) in each of the 12 months of the flipbook. Which line on the graph most closely matches the pattern of NDVI values through the year?
4.The worksheet has questions for each land cover type. These questions along with the definitions of the land cover types should help to classify the lines on the graph with the land cover type that produced it.
Questions to turn in
Answer in complete sentences and cite numeric evidence from the graph (such as the maximum and minimum values and the months in which they are reached) for full credit
1. (2 pts) What is land cover #1 (solid triangles)? What evidence did you use to come to this conclusion?
2. (2 pts) What is land cover #2 (open squares)? What evidence did you use to come to this conclusion?
3. (2 pts) What is land cover #3 (open circles)? What evidence did you use to come to this conclusion?
4. (2 pts) What is land cover #4 (open triangles)? What evidence did you use to come to this conclusion?
5. (2 pts) What is land cover #5 (solid circles)? What evidence did you use to come to this conclusion?
Visiting landcover types
Next, we are going to visit some of the landcover types using the website Confluence.org. This is a collaborative project in which people who have GPS (Global Positioning Systems) visit confluences (whole degree intersections of latitude and longitude) and take pictures of the location. For the following locations, describe the landcover that you see, and using the latitude and longitude and the Natural Vegetation map on pages 24 and 25 of your atlas, identify the vegetation type (the letter code).
Example:
36*N 101*E. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type (the letter code).
This landcover appears to be mostly bare ground with a few dead-looking small plants. According to the Natural Vegetation map is it Gp, Grasses and other herbaceous plants, growth singly or in groups or patches.
6. (1 points) 62*N 130*E. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type (the letter code).
7. (1 points) 3*N 115*E. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type(the letter code).
8. (1 points) 10*N 10*E. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type(the letter code).
9. (1 points) 41*N 101*W. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type(the letter code).
10. (1 points) 71*N 80*W. In one to two sentences describe the landcover as you see it in the pictures, then locate this site on the Natural Vegetation map on pages 24-25 of your atlas and identify the vegetation type(the letter code).
11. (5 pts) In two or more paragraphs, discuss the patterns of green up and senescence around your home. Where do you live? How do these patterns relate to the seasons and the amount of available insolation? NOTE: Please discuss the region around your house, and not gardens and cultivated plants. These plants are watered, and usually not from your area, so are not good indicators.
Answers to Check your Comprehension
1. What does the color dark green indicate?
Dark green indicates a high vegetation vigor. In other words, the plants in this region are using the majority of the sunlight available.
2. What does the color light green indicate?
Light green indicates a low vegetation vigor. In other words, the plants in this region are not growing very much, indicative of senescence.
3. What patterns do you notice between landcover as it is classified in Figure 2 and the regions that are dark green in both January and July (Figure 1)? What about the regions that are light green in both January and July?
The dark green areas in both January and July correspond to ‘Broadleaf evergreen’ or tropical rain forest. The light green areas are ‘Shrubs, desert and bare ground’. This makes sense because evergreen leaves never fall off – in other words they grow all year. The desert is very dry, which is not hospitable to growing plants. Note, however, that the deserts do green up slightly in January.
4. Which hemisphere has a stronger vegetation vigor in January? Which hemisphere has a stronger vegetation vigor in July?
As with hemispheric seasonal patterns, vegetation patterns are reversed between the hemispheres. Further the much stronger seasonal change in the Northern Hemisphere results in a much more pronounced rise and fall to its vegetation.