Plant Community Assessment using Transects in the Field

This lesson has four major aims:

  1. To teach desert ecology
  2. To teach local plant identification and adaptations
  3. To introduce students to field biology and to the transect in particular as a method of data collection
  4. To demonstrate differences in plant community with habitat
  5. To familiarize students with methods of extrapolating their data and the assumptions that one makes when making such extrapolations

Equipment provided:

  1. Compass
  2. Stake with 100 cm string attached
  3. Clipboard with data sheet (see below)

Equipment teachers should bring:

  1. Calculators (4-5)
  2. I ask that a copy of the data collected remain (or be sent) here so that comparisons with future classes can be made

Introduction to students:

  1. Overview of desert ecology
    • Description of different habitats within the system
    • Importance of water in shaping the system
  2. Challenges desert plants face
  3. Plant identification and adaptations
  4. Biological diversity in the desert as overarching theme

Assignment to students: they are biologists charged with the duty of assessing the plant community of this area which has been set aside for potential preservation

  1. Introduce concept and practical use of transect data
  2. Assign groups of 3-4 students to one of five transects set in different habitats
    • Depending on time constraints, transects in various habitats can be conducted in 1, 2, or 3 separate sites for additional comparison
  3. Transect Methods
    • Data points on the transect
    • At each point students place the stake into the ground, extend the string and walk a ring around the stake counting how many of each species of plant that are found within the ring
    • 10 data points are taken (with about 12 paces between each point)
  4. Students use the compass to ensure that they are walking a straight line North
  5. Totaling and Extrapolation
  • Discuss the degree of usefulness achieved with totals and percentages of each plant on the transect(s)
  • Demonstrate how with some very simple math, we can extrapolate our data over a larger area
  • Extrapolating for an acre
  • area of the ring important
  • #plants/acre = 20 X #plants in the 10 transect points (rings)
  • Extrapolating for a square mile
  • 1 square mile = 640 acres
  • #plants/square mile = 640 X #plants/acre
  • Discuss their results and how important the ability to extrapolate is when making conservation decisions in the real world
  • Discuss the assumptions we are making when we extrapolate and the importance of repeated sampling in all habitat types

If transects are repeated at the different sites, class can use the data to perform some simple statistics in the classroom to determine variability within habitat at different sites