Leaf Idenification Lesson: Part 2

Maple or Maple-like leaves. Images from Leafsnap.com

The students turned in their completed leaf ID booklets late last week and I was able to look them over and collect the data from their books.  I would have preferred to have the students collect and graph the data, but we were running up against time constraints so I prepared a graph for class. I noticed that there was some confusion over identification of various species of maple-looking trees (genus: Acer), so I created a slide to point out the differences to the students.  I put the slide up with the common names hidden and asked the students whether they could identify the leaves.  I was very surprised and impressed when both classes were able to correctly identify all five leaves!!  They really learned something!  Next I shifted the discussion to the data that I had synthesized.  First, I presented data from each class in an Excel spreadsheet.  I asked students if they had any ideas about how to present the information so that we could easily get some useful information from the jumble of numbers.  After some discussion, students settled on a bar graph because we could easily show how many leaves came from each category.  I then showed them a pre-made bar graph of their class’s data.  We identified the most common tree species within each class and discussed whether this was conclusive evidence that we identified the most common tree species in all of Boston.  Students suggested several reasons why we could not be sure that our evidence was conclusive:

  1. Most students had collected their leaves from around the school area, thus many of the leaves were from the same trees and didn’t tell us much about the rest of Boston.  This is a geographic bias.
  2. The amount of leaves students had collected, even when combined together, was very small compared to all the trees in Boston.  Our sample size was small.
  3. The assignment had specified that students collect 5 leaves from 5 different species rather than collect whatever happens to be around.  If one or two trees were clearly dominant in Boston, our classes would have over-sampled the rarer species and under-sampled the main species.  This highlighted our sampling bias.

To address one of these issues, sample size, we were able to combine data from all three classes to get a better sense of what had been collected and identified. Among our three science classes, sugar maple, red maple, and Norway maple were the most frequently identified leaves. Although our sample size is still too small to make strict conclusions, we can comfortably say that these three species are fairly abundant in the region of Boston near John D. O’Bryant school and its students’ neighborhoods.

Data from leaf identification class for the 1st, 3rd, and 6th period 8th grade science classes at the O'Bryant school, October 2012. (Click to enlarge.)

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