Measuring stand basal area

(60 points)

This project gives you a chance to compare two methods for estimating tree basal area. You will need the "cruiser's crutch," radius cord, and diameter tape from your equipment kit.  (Note: In special circumstances you might have to adjust the length of the radius cord.  If most quadrats would have more than 12 trees or fewer than five trees, you can change the length of the cord.)

You don't have to be able to identify trees to species for this project. You just have to distinguish trees (woody plants with single trunks) from shrubs (woody plants with multiple trunks at ground level) and herbs.

(Special note: If you live in an area with no trees, contact me to arrange a replacement project.)

Procedure

1. The study area. You should pick a study area that is forested, that you have access to, that is at least 60 m on each side, and where it won't matter if you trample some plants.
2. The sampling universe. Mark the boundaries of your study area: all your measurements will be inside these boundaries. At this stage in the course you will not be using a statistical sampling design, but it is a good idea to practice defining the sampling universe anyway.
3. Sample locations (five in total). Select an arbitrary sample location by throwing the surveyor's pin over your shoulder. (If you were doing this for real, locations would be strictly random, something covered in a later chapter.)
4. Quadrat measurements. Stake the radius cord at the sample location. Measure the diameter of each tree that is in the circular quadrat defined by the radius cord. Use the diameter tape to measure tree diameter.
5. Bitterlich or angle gauge measurements. Decide which basal area factor you will be using with your cruiser's crutch. Aim for counting 8-12 trees per location. Use the same sample location you used for the quadrat measurements. Hold the eye over the location point and rotate your body to scan the stand for trees that are "hits."
6. Repeat the quadrat and prism measurements for four more locations scattered across your sampling area.
7. Estimate stand basal area using the calculations in the "How to Measure" chapter.

Report

1. Describe your study area in a paragraph, noting its geographical location, topography, and appearance. Include a photograph of your study area if you have access to a camera. How did you define and mark the boundaries of your sampling universe?
2. Attach a spreadsheet with your raw data and calculations. The raw data are each measurement of tree diameter and the number of hits per location.
3. Describe how you made sure you got a clear view of each candidate tree when using the Bitterlich method.
4. Report your estimate of overall stand basal area for each method. Show your calculations in the spreadsheet, how you got from individual measurements to overall estimates.
   • Hint: Pay close attention to the units of measurement.
5. For each method, calculate 90% confidence intervals for the overall estimates of stand basal area.
6. Did the quadrat and prism measurements give similar answers? Why do you think that is?
7. For 540 students
   • What is your subjective assessment of the inherent accuracy of the methods?
   • Compare the precision and efficiency of the two methods.
   • How would you change your technique if you were to use the methods in the future?

For students enrolled in BOT 440, limit your report to one page of single-spaced text, not including tables, figures, and data forms. For students enrolled in BOT 540, limit your report to 1.5 pages of single-spaced text, not including tables, figures, and data forms.

Version: May 31, 2008