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In the online forest sampling tutorial given, I have chosen to do 1. Random sampling using area, 2. Systematic sampling along a topographic gradient using distance, and 3. Haphazard sampling using area. The Haphazard method had the fastest estimated time to sample at 2h38min, compared to 12h47min for the random sampling method, and 4h7min for the systematic sampling.
According to actual data, the two most common species in the Snyder-Middleswarth Natural Area were Eastern Hemlock and Sweet Birch. Let us use tables to compare the % error of the different sampling strategies for both.
| Species | Measures | Actual
Data |
Data for
The Random Sampling Method |
Data for
The Systematic method |
Data for
The Haphazard method |
% Error
Random Sampling |
% Error
Systematic Sampling |
% Error
Haphazard Method |
| Eastern
Hemlock |
Density | 469.9 | 354.2 | 479.0 | 380 | 24.6% | 1.94% | 19.13% |
| Frequency | 73% | 71% | 70.8% | 80% | 2.7% | 3.01% | 9.6% | |
| Dominance | 33.3 | 19.8 | 35.5 | 39.6 | 40.5% | 6.61% | 18.92% | |
| Relative Density | 50.6 | 44.0 | 54.2 | 43.2 | 13% | 7.11% | 14.62% | |
| Relative Frequency | 33.8 | 32.1 | 37.0 | 33.3 | 5.1% | 9.47% | 1.48% | |
| Relative
Dominance |
44.4 | 45.6 | 53.6 | 54.7 | 2.7% | 20.72% | 23.2% | |
| Importance
Value |
42.9 | 40.6 | 48.2 | 43.7 | 5.4% | 10% | 1.86% | |
| Morisita Index | 1.89 | 2.33 | 1.05 | 1.35 | 23.3% | 44.44% | 28.57% | |
| Sweet Birch | Density | 117.5 | 41.7 | 64.5 | 60.6 | 64.51% | 45.11% | 48.43% |
| Frequency | 43.0% | 25% | 29.2% | 20.0% | 41.86% | 32.09% | 53.49% | |
| Dominance | 20.2 | 5.1 | 11.3 | 8.4 | 74.75% | 44.06% | 58.42% | |
| Relative Density | 12.7 | 5.2 | 7.3 | 6.8 | 59.05% | 42.52% | 46.46% | |
| Relative Frequency | 19.9 | 11.3 | 15.2 | 8.3 | 43.21% | 23.62% | 58.29% | |
| Relative
Dominance |
26.9 | 11.8 | 17.1 | 11.6 | 56.36% | 36.43% | 56.88% | |
| Importance
Value |
19.8 | 9.4 | 13.2 | 8.9 | 52.53% | 33.33% | 55.05% | |
| Morisita Index | 2.27 | 3.20 | 0.00 | 5.00 | 40.97% | 100% | 120.26% |
Then, let us do the same thing for the two most rare species; Striped Maple and White Pine.
| Species | Measures | Actual
Data |
Data for
The Random Sampling Method |
Data for
The Systematic method |
Data for
The Haphazard method |
% Error
Random Sampling |
% Error
Systematic Sampling |
% Error
Haphazard Method |
| Striped Maple | Density | 17.5 | 0.0 | 18.4 | 60.0 | NA | 5.14% | 242.86% |
| Frequency | 6.0% | 0.0% | 4.2% | 20.0% | NA | 30% | 233.33% | |
| Dominance | 0.7 | 0.0 | 0.6 | 3.6 | NA | 14.29% | 414.29% | |
| Relative Density | 1.9 | 0.0 | 2.1 | 6.8 | NA | 10.53% | 257.89% | |
| Relative Frequency | 2.8 | 0.0 | 2.2 | 8.3 | NA | 21.43% | 196.43% | |
| Relative
Dominance |
0.9 | 0.0 | 1.0 | 5.0 | NA | 11.11% | 455.55% | |
| Importance
Value |
1.8 | 0.0 | 1.7 | 6.7 | NA | 5.56% | 272.22% | |
| Morisita Index | 17.00 | NA | 24.00 | 5.00 | NA | 41.18% | 70.59% | |
| White
Pine |
Density | 8.4 | 8.3 | 0.0 | 20.0 | 1.19% | NA | 138.09% |
| Frequency | 4.0% | 4.0% | 0.0% | 20.0% | 0% | NA | 400% | |
| Dominance | 0.9 | 1.1 | 0.0 | 0.4 | 22.22% | NA | 55.55% | |
| Relative Density | 0.9 | 1.0 | 0.0 | 2.3 | 11.11% | NA | 155.55% | |
| Relative Frequency | 1.9 | 1.8 | 0.0 | 8.3 | 5.26% | NA | 336.84% | |
| Relative
Dominance |
1.2 | 2.5 | 0.0 | 0.6 | 108.33% | NA | 50% | |
| Importance
Value |
1.3 | 1.8 | 0.0 | 3.7 | 184.62% | NA | 184.62% | |
| Morisita Index | 16.13 | 24.00 | NA | NA | 48.79% | NA | NA |
For the Shannon-Weiner diversity index (not shown in above tables), the most accurate measure was the one given by the random sampling method using area which was giving the exact same figure as actual data: 1.5. However, looking at the % error for the two most common and two rarest species, accuracy greatly varies within the three sampling strategies depending on the measure and the species concerned. For the Sweet birch, the % error was extremely high for all three methods, and in all measures. As for the striped maple, the systematic method was the most accurate, given that the random sampling method did not account for any tree of that species, while the % error of the haphazard method was considerably higher than for the systematic sampling. Finally, the random sampling method was the most accurate for the white pine species. Its percentage error was noticeably lower than in the systematic sampling, and the haphazard method did not provide any data for the white pine. Before doing this tutorial, I was expecting that accuracy would increase in the same direction as species abundance, so I was quite surprised to see how far off were the results for the sweet birch species measures. After doing this tutorial, I realized that for an area as wide as the Snyder-Middleswarth Natural Area, it would have been preferable to use more than 24 samples for better accuracy.
H. Zulfiqar
