High school students practice skills interpreting graphs and drawing conclusions while learning about North American plant diversity and distribution. First, they investigate current patterns of plant diversity and distribution across North America, exploring broad latitudinal gradients of species richness and climate influences on vegetation type. Second, they build on this knowledge to predict changes based on current projections on global warming.

Several enrichment activities focus on regional and local patterns of plant diversity and distribution. This shift allows students to grasp the importance of scale in ecology. Students have opportunities to explore the roles of biotic and abiotic factors, the natural changes during ecological succession, and the impact of introduced species on diversity and distribution.

Background
The North American continent treated in the Flora of North America covers 21.5 million km 2 of land, north of Mexico to the limits of plant life in the artic. It stretches between latitudes 26º and 85ºN, between longitudes 15ºW and 173ºE, and from sea level to high mountains. This great and varied landscape is home to about 20,100 plant species (about 21% of those are endemic). North America has most of the major land biomes found around the world: tundra, taiga, temperate forest, chaparral, grasslands, and deserts. Tropical forests and savannas are absent because the continent is centered in the temperate, not the tropical, zone.

Over Earth's long history the climate has shifted. The distribution of plants in North America has shifted too. Biomes map of ice-age periods and current conditions are strikingly different. Mean annual temperature during the last full-glacial period was about 6ºC lower. An ice sheet covered the northern half of North America. When warming began 18,000 years ago, this ice sheet retreated to the Arctic Circle and plants (such as spruces, pines, and oaks) advanced northward. Ice-age communities also included combinations of plants not seen today. Soil cores and fossils provide evidence of past conditions.

We rely on scientific predictions for an outlook on the future. Earth's climate has warmed by 0.6ºC in the last 100 years. The global climate is predicted to be 1.4 to 5.8ºC warmer by the end of this century. Plants are already responding to global change in some ways that meet predictions.

At high latitudes and alpine areas, where climate change is expected to be most severe, plant communities are shifting distribution. Shrubs are shifting northward and expanding into the Arctic. The treeline in North America, Europe, and New Zealand is advancing to higher elevations up mountain slopes. Plants in the Alps are shifting up slope by 1-4 meters in elevation per decade. Regional shifts in the distribution of particular plants species are expected. Responses in plant physiology and reproduction are also occurring. The length of the growing season in some areas has increased by about 3.6 days per decade over the last 50 years. What kinds of changes are expected (or already reported) in your region?

Minds-on Activities (Student Worksheets)

• Plant Number Game - Interpret patterns of plant diversity across North America
• Mapping North American Biomes - Analyze climate graphs and vegetation maps
• Charting Climate Change Effects - Predict future changes in plant distributions

Enrichment Activities

• Why are some plant groups found in eastern North America and eastern Asia? Research how and why the distribution of plants such as Liriodendron or Cornus have changed over time.
• What patterns of diversity and distribution can you see in your schoolyard, backyard, or local park? As a class project, survey local diversity and distribution by sampling at least two vegetation plots. Identify differences in the plots and suggest explanations for patterns; then collect data to test the hypotheses (see the Lesson Exploring Local Biodiversity for details).
• Grasslands once covered 25% of North America, and the large bison herds that once ranged across the region are all but gone. Create a map of past distribution patterns for prairies and bison (or prairie dogs). What role do animals play on a prairie? What about fire?
• Do human activities help or hinder the natural cycle of ecological succession after a volcanic eruption, a major hurricane, or forest fire? Research a case study of ecological succession, such as Mount St. Helen's or Yellowstone National Park. Illustrate the natural stages from pioneer community to climax community, indicating how human actions can alter the process.
• Which introduced plants are problems in your region? Design a study on an invasive plant pest. Here are some starting questions: How quickly has the plant spread? Does it negatively affect native plants or animals; if so, how? What is the most effective way to control or permanently remove the plant?
• If land biomes cover only about 25% of the Earth's surface, what biomes cover the rest? What characteristics are important in describing these biomes? Map the global distribution of estuaries. Why do estuaries support so many organisms?
• Is the evidence for global warming convincing? Evaluate the evidence. Write a letter to the President of the United States, a senator, or a representative supporting or opposing the official position based on your evaluation of the evidence.

Explore more!
MBGNet – Missouri Botanical Garden’s Education Department has biome photos and facts.

Suggested Readings and Resources
Bartlein, P. J., Whitlock, C., and Shafer, S. L. 1997. Future climate in the Yellowstone National

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