One issue which has bedeviled me in preparing for service-based learning and Citizen Science is how to give the students enough information that they can intelligently perform the investigation. In the Urban Forest program, we had a limited number of variables:
- Species of tree
- Diameter of trunk at 4.5 feet
- GPS (global positioning system) location of tree (i.e., its latitude and longitude, accurate to 4 decimal places)
- 12 leaf samples from tree
- Qualitative description of health of tree (good, fair, poor, dead)
But let’s everything that’s involved. First, the student has to be able to identify the tree. This is not at all easy, and it’s not the most interesting thing to learn, which is why I think that most teachers don’t attempt it. Any park has at least a dozen species of trees in it. I finally decided that what we needed to do before venturing to a park was to do a trial run on the school grounds. This made sense because I could limit the number of species to six trees:
- California pepper (Schinus molle)
- California sycamore (Platanus racemosa)
- Chinese elm (Ulmus parvifolia)
- Jacaranda (Jacaranda mimosifolia)
- Mulberry (Morus (many species))
- Indian laurel aka Ficus (Ficus microcarpa)
With a limited set of tree species that were fairly distinct from each other, we had a manageable number that the students could master without feeling overwhelmed, and would give the UC Riverside folks a varied set of data from different but quite common trees. (The mulberry was the only tree I haven’t seen much of in parks and on the street, although they are popular trees in California, particularly on south and western sides of houses, since they are deciduous: leaves when it’s hot, and no leaves when it’s cold.)
Our school is located in central Hollywood between Sunset and Hollywood Boulevards and 2 blocks west of Hollywood High (yes, there is such a school!). Here is a decent aerial view of it from Google Earth:
The street running along the bottom is Selma, and the large blacktop area is the school playground. It’s ringed with trees that should be visible to the NASA fly-over, and didn’t require us to cover acres and acres of ground.
Although the other things to be done were fairly easy—evaluate the health of the tree, measure its diameter, gather samples, and locate its position with the GPS—getting it done as a group presents complexities, particularly if you’re working with middle-school students. You have to figure out the right number of people for each group, get some idea of what the job duties of each are, and train them in whatever techniques they won’t get immediately.
Since I had nine students, three was the magic number. On many activities, I prefer pairs, as it’s impossible for anyone to hide from doing the work with only two. With four or five, you’re always going to have somebody gossiping or shirking. Three seemed appropriate for this task, since there were plenty of things to do simultaneous.
The hardest task to instruct was the use of the GPS. I anticipated this, and gave the students on the school day before we took the measurements a kind of scavenger hunt, where they had to take the units and locate where various positions were. I had not had time to look the units over before we started, which was a mistake. One of them had failing batteries, and I spent the entire class period trying to figure out how to open the battery container! (Also, another reminder that I need a multimeter to test batteries for voltage.) I also learned that you can’t simply hand the device off and have the students go off and figure them out. The major difficulty here was that the GPS units were quite accurate, but took up to 4 minutes to equilibrate (must have been sampling from multiple satellites). One of the exercises I had planned for them was to find a specific latitude and longitude, which I’d already determined with my Android tablet. Easy on the tablet, not so easy on the GPS. Lesson to teacher: always read the manual cover to cover before handing off to the students, and do the exercise with the equipment you’ll use. (The kids still liked the scavenger hunt, and I recommend it as a technique for teaching proper use of equipment.)
Diameter tapes for trees can be a little tricky. The circumference of a tree is defined as pi times the diameter (πd), although most students learn the circumference formula as 2πr, where r is the radius. Ideally, students should recognize the first formula as a simple algebraic substitution of d=2r, but algebra isn’t the flavor of the century in present-day America. Anyway, you can measure the circumference and then divide by 3.14 (a good-enough approximation of π) to get the diameter, or by 6.28 to get the radius. I guess because people don’t like to divide, there are diameter tape measures that you can wrap around the tree. You can see one of them below.
The nice thing about these is that you don’t have to do calculations. The bad thing about them is that the tapes typically have two sides, one of which is a regular tape measure (which you use to measure the height off the ground), and if you use the regular measure around the tree, you’ll be reporting a diameter that’s more than three times too large. I speak from sad experience. In our Earthwatch training on the project, somebody reported a tree with a diameter of no more than a foot as having a diameter of almost 40 inches. I thought it was measurement error, until I got the same result. It was a real puzzle until it occurred to me that I was using the wrong side of the tape! Use the right side, get the right result. Not a bad mistake to make when you’re preparing to train students.
One difficulty I didn’t expect was the use of pruning poles that Earthwatch had provided to us to get samples that were out of reach. Having been raised in suburban settings, I’ve pruned more trees than I can remember. My kids were really excited to see the pruning poles….because they’d never seen or used them before. So we needed a few minutes on their safe operation and how to extend them to the necessary height. One lesson that always repeats itself for all teachers is that your students don’t share your life experiences. The students quickly mastered the use of the poles, as you’ll see in the next post.
One complicated part of the project is the record keeping. While I gave the students quite a bit of leeway in terms of who did what, it was clear that a dedicated record keeper was necessary. There was quite a bit of information to record, and the samples had to be stored in plastic bags with wet towels. The procedure is not complicated, but there are a bunch of things you have to do. We talked it through beforehand and everyone had a good idea of what was necessary. As I expected, it took a couple of passes until they got proficient at all the tasks, and then the sample taking sped up. The next post will have photos documenting their progress.