Biomes, Vegetation Structure, and Canopy Height

Mary Mulcahy, University of Pittsburgh at Bradford


Summary

Students will develop a concept of vegetation structure and biomes through an exploration of field site data from the National Ecological Observatory Network (NEON) project. Students will compare characteristics of major groups of plants with respect to heat and drought tolerance, develop hypotheses for how canopy height may vary by several abiotic factors, and evaluate their hypotheses using graphed data, trendlines, and r-squared values.

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Learning Goals

  • Compare characteristics of major groups of plants with respect to drought and heat tolerance
  • Construct hypotheses about the relationship between biotic and abiotic variables
  • Test hypotheses through visualization data
  • Use the r-squared statistic to numerically evaluate the strength of a linear relationship between two variables
  • Draw conclusions supporting or refuting hypotheses based on evidence and statistics

Context for Use

  • Developed for introductory college biology courses for non-majors or majors, but could be adapted to other education levels
  • Module is divided into three activities completed in three separate 50-minute sections, two 75-minute sessions, or one 3-hour session
  • Activity can be conducted online or in-person. Access to computers is required if activity is to be completed entirely in-class. If student computers are not available, instructor could model Activities A & B in class and assign Activity C as homework
  • Students choose what variables to explore in Activity C
  • Instructions are detailed enough for students to complete entirely independently if needed

How Instructors Have Used This Module

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Using Project EDDIE modules in Introduction to Biodiversity
Mary Mulcahy, University of Pittsburgh-Bradford
This module is intended to encourage beginning college students to take a second look at plants. This module will introduce students to the remarkable natural vegetation and ecological habitats in the United States through exploration of canopy height and abiotic factors found at the core terrestrial field sites of the National Ecological Observatory Network (NEON) project.

Description and Teaching Materials

Outline

  • Pre-Assignment (optional)
    • Compare major groups of plants with respect to tolerance of heat and drought
  • Activity A: Do temperature and precipitation predict biome?
    • Make predictions about biomes for particular US locations using Whittaker's biome diagram
    • Confirm the actual biome using NEON field site land cover descriptions
    • Compare and contrast the term "biome" with "National Land Cover Database Class"
  • Activity B: Does canopy height vary by growing season length?
    • Construct hypothesis about how and if canopy height varies by growing season length
    • Graph NEON field site data and evaluate the hypothesis
    • Use slope and r-squared values to understand the relationship between two variables
  • Activity C: Does canopy height vary with temperature and precipitation?
    • Construct hypotheses about how and if canopy height varies by precipitation and temperature.
    • Graph NEON field site data to evaluate the hypotheses
    • Explore the relationship between two variables of choice

Workflow of this module:

Pre-Assignment (optional)

  1. Students are asked to watch several videos that describe hydraulic stress and the effects of leaf shape and size on leaf temperature.
  2. Students fill in a table comparing the majors groups of plants with respect to adaptations to drought and heat tolerance.

Activity A

  1. Instructor introduces the concepts of vegetation structure, canopy height, and biomes and introduces Whittaker's biome diagram. PowerPoint presentation includes questions to facilitate introduction to module.
  2. Class works together to predict the biome for the first location; guided instructions included in the PowerPoint presentation. To use time efficiently, assign different groups to different NEON field sites and have the class share data.
  3. If student computers are available, students work individually or in small groups to answer remaining questions in the student handout for Activity A. If computers are not available, the instructor can lead a class discussion for the entire student handout.
  4. Reconvene class to share data and for discussion of the question set for Activity A, especially why Whittaker's biome diagram shows that forest is restricted to areas with more than 50 cm of precipitation per year, but grasslands persist in conditions below 50 cm annual precipitation. (Revisit concepts from slides 15 & 16 in the PowerPoint file or in the Supplemental Table A from the Pre-Assignment.) 

Activity B

  1. Instructor leads the entire class through testing hypotheses about the relationship between canopy height and growing season length in the NEON Field Site Data.

Activity C

  1. Activity C follows the process used for Activity B, but students work with greater independence than in Activity B to test hypotheses of canopy height in relation to temperature and precipitation (the two variables found in Whittaker's biome diagram).
  2. As a final exercise in Activity C, students develop and test a hypothesis about the relationship between two variables of their choice from the dataset.  

Teaching Materials

Teaching Notes and Tips

This activity requires access to the internet. Although this module is developed for an introductory biology class where the students utilize data that is pre-imported and ready for easy graphing in CODAP, the module could be modified to allow students to download the CSV file directly from NEON to create graphs or to do analysis in R or another platform.

Assessment

Students will answer questions throughout the activity that will demonstrate comprehension. Assessment was also completed through pre-activity and post-activity questions developed by the author and available upon request.

References and Resources

Common Online Data Analysis Platform "Codap" [Computer software]. (2022). Concord, MA: The Concord Consortium.

NEON (National Ecological Observatory Network). Explore Field Sites. NEON Field Site Table. https://www.neonscience.org/field-sites/explore-field-sites (accessed 16 April 2022). Imported into Codap: Codap file for Activity B & C

Moles, A.T., Warton, D.I., Warman, L., Swenson, N.G., Laffan, S.W., Zanne, A.E., Pitman, A., Hemmings, F.A. and Leishman, M.R. (2009). Global patterns in plant height. Journal of Ecology, 97: 923-932.https://doi.org/10.1111/j.1365-2745.2009.01526.x

Ryan, M. G., & Yoder, B. J. (1997). Hydraulic limits to tree height and tree growth. BioScience, 47(4), 235–242. https://doi.org/10.2307/1313077

Pre-assignment Videos: 

Hydraulic Damage by by Jim Ehleringer and Steve Kannenberg, Plant Ecology in a Changing World (Biology 5460) YouTube Channel, University of Utah,  https://youtu.be/bZu8Q_hJd_g

How trees bend the laws of physics by Derek Muller, Veritasium YouTube Channel, https://youtu.be/BickMFHAZR0

Leaf shape, leaf size, and leaf temperature by Scott Turner, Scott Turner's (macrotermiteman) YouTube channel,  https://youtu.be/gOFK4OeS4MI