An interactive exercise for FORS 333: Fire Ecology at the University of Montana. Students use field data collected in the footprint of the 2017 Lolo Peak Fire to see how to summarize a site, how sample size affects the mean and its standard error, and whether fewer transects can still detect change between years.
Open the exercise: https://higueralab.github.io/post-fire-sampling-exercise/
The exercise has three tabs:
- Summarize 16 plots. Live seedling density in the 16 plots sampled at the high-severity site (LP_H) in 2026. Toggle the mean, median, range, mean ± 1 SD, and mean ± 2 SE to compare ways of describing central tendency and variability.
- Fewer plots? Draw repeated random samples of n plots from the 16 and watch the sample means build into a bell-shaped distribution (the central limit theorem). Compare the spread of sample means with the prediction SD/√n.
- Detect a change? Compare fine litter cover at LP_H between two years. Choose how many transects were sampled per year, and see how often the ±2 SE error bars separate across 1,000 random subsets.
Terms. A site (LP_H, LP_M) is characterized by a sample of sampling units: belt transects from 2018 to 2025, and 1-m-radius plots in 2026. The sample size, n, is the number of transects or plots.
Course rule for significance. Two means are called significantly different when their ±2 SE error bars do not overlap. This rule is conservative: it rarely flags a difference that is not there, but it misses some real differences that a formal test would detect.
All values are embedded in index.html. No data are loaded from the web.
- Tabs 1 and 2: live tree seedlings (all species combined) per plot, LP_H, 2026, n = 16 plots. Species absent from a plot count as zero.
- Tab 3: fine litter cover (<7.6 cm diameter) per belt transect, LP_H. Each value is the mean of a transect's two cover circles. Years: 2018, 2019, 2022 to 2025 (2020 and 2021 were not sampled).
The data were collected by FORS 333 students between 2018 and 2026. Tab 2 draws plots with replacement (a bootstrap). Tab 3 draws transects without replacement from each year.
- Online: open the link above in any current browser.
- Offline: download
index.htmland open it in a browser. It needs no internet connection or installation.
- Code (HTML, CSS, and JavaScript): MIT License.
- Text, figures, and embedded class data: Creative Commons Attribution 4.0 International (CC BY 4.0).
Higuera, P. E. (2026). Lolo Peak Sampling Exercise [Interactive teaching tool]. FORS 333: Fire Ecology, University of Montana. https://github.com/HigueraLab/post-fire-sampling-exercise
The exercise was developed by P. Higuera with AI assistance (Claude, Anthropic), and reviewed by the author.
Philip Higuera, Department of Ecosystem and Conservation Sciences, W.A. Franke College of Forestry and Conservation, University of Montana. philip.higuera@umontana.edu