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In the Virtual Forest tutorial, using Distance-based sampling methods:
Table 1. Comparison of three distance-based sampling strategies; actual, random, and haphazard used to calculate the abundance of seven tree species (Eastern Hemlock, Sweet Birch, Yellow Birch, Chestnut Oak, Red Maple, Striped Maple, and White Pine) in the Snyder- Middleswarth Natural Area.
| Tree Species | ||||||||
| Strategies | Eastern Hemlock | Sweet
Birch |
Yellow
Birch |
Chestnut
Oak |
Red
Maple |
Striped
Maple |
White Pine | Est. Time to sample |
| Actual | 469.9 | 117.5 | 108.9 | 87.5 | 118.9 | 17.5 | 8.4 | |
| Systematic | 277.3 | 109.6 | 70.9 | 38.7 | 90.3 | 45.1 | 12.9 | 4hr 18min |
| % error | 40.99 | 6.72 | 34.89 | 55.77 | 24.05 | 157.71 | 53.57 | |
| Random | 441.8 | 144.1 | 105.6 | 115.2 | 86.4 | 28.8 | 0.0 | 4hr 40min |
| % error | 5.98 | 22.64 | 3.03 | 31.66 | 27.33 | 64.57 | 100 | |
| Haphazard | 485.0 | 121.2 | 83.9 | 93.3 | 74.6 | 18.7 | 18.7 | 4hr 38 min |
| % error | 3.21 | 3.15 | 22.96 | 6.63 | 37.26 | 6.86 | 122.6 | |
Based on findings from Table 1:
Which technique had the fastest estimated sampling time?
The times between the 3 sampling strategies were somewhat similar, with the fastest strategy by ~20 minutes being the systematic approach in regards to sampling 24 plots.
Comparing the % error of the different strategies for the two most common and two rarest species. For each species the most accurate strategy was as follows:
- Eastern Hemlock (most common species) most accurate strategy: Haphazard
-
- It surpasses the random strategy with an % error of 3.21.
- Than random & haphazard strategies were more accurate than the systematic, as the systematic had an % error of 40.99.
- Red Maple (second most abundant species) most accurate strategy: Systematic
-
- This strategy had a 24.05% error.
- White Pine (rarest species) most accurate strategy: Systematic .
- Even though it had a 53.57% error, it is far more accurate than the random & haphazard strategies with % errors of 100, and 122.6, respectively.
- Striped Maple (second least abundant species) most accurate strategy: Haphazard.
-
- This strategy had a 6.86 % error which is very low, especially when compared to 64.57% and 157.71% errors for Random and Systematic, respectively.
Did the accuracy change with species abundance?
When comparing all three strategies regardless of tree species, accuracy decreased as species abundance lowered. Therefore, I recommend that more samples than 24 need to be taken to increase accuracy. The majority of % error was inversely proportional to the actual species abundance (save for a few data points), regardless of the sampling strategy.
Was one sampling strategy more accurate than another?
Haphazard strategy had an average % error of 28.96, which is lower than that for Random & Systematic (36.46% & 53.39%, respectively) – there by being the most accurate sampling strategy in a forest terrain. The random strategy being the least accurate.
