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Community Sampling Exercise by Carmen Bell
Community: Snyder-Middleswarth Natural Area
The three virtual sampling strategies used to assess species density for the Snyder-Middleswarth Natural Area included random, systematic and haphazard. Of the three, the area-based haphazard sampling method was the fastest at 12 hours, 12 minutes, likely because these are known representations of the larger area taken in a non-random manner. The longest duration was the area-based random or systematic method of 12 hours, 45 minutes. The difference in time between the two is not vast for the 24 plots, however, the difference may increase given more sample points.
| 1. Area, random or systematic | 2. Area, random or systematic | 3. Area, haphazard |
| 12 hours, 35 minutes | 12 hours, 45 minutes | 12 hours, 12 minutes |
For the total area of the Snyder-Middleswarth Natural Area, 24 sample points were not enough to represent the diversity of the 200ha old-growth hemlock-yellow birch forest. In effect, each sample point represents 8.3 hectares (20.6 acres) over the steep terrain of a ravine created by the Swift Run River. As this is a virtual exercise, the representation can only be imagined. In a real case scenario, the accuracy represented in the sample points would depend, in part, on the variation of soil composition within the degrees of steepness.
My assessment of the histograms from a perspective of relative species abundance, determined that the Eastern Hemlock and Sweet Birch be considered common, while the remaining species be considered rare. Within the context of biodiversity, “…, n individuals usually fit a hollow curve, such that most species are rare … and relatively few species are abundant” (McGill, et al., 2007). Each of the Yellow Birch, Chestnut Oak, Red Maple, Striped Maple and White Pine had a relatively hollow curve given the limited data. The Snyder-Middleswarth Natural Area is known as an old-growth hemlock-yellow birch forest. The lower density of yellow birch could be attributed to the larger stem size of an old growth tree.
Considering the Eastern Hemlock and Sweet Birch as the most common species, the most accurate density reading was the Eastern Hemlock with a 10.6 percentage error between the known and sampled data. Considering the Yellow Birch, Chestnut Oak, Red Maple, Striped Maple and White Pine species as rare, the most accurate density reading lay with the Striped Maple at 14.3% error. I would like to point out that only 20 trees were sampled with a known density of 17.5. The Yellow Birch had a higher percentage of error at 30.2, however, the known density is 108.9 with 76.0 represented in sample data, demonstrating a stronger representation of the species.
Eastern Hemlock
Actual Data
| Density | 469.9 | 520.0 |
520.0 – 469.9 / 469.9 x 100 = 10.6% percentage error
Sweet Birch
Actual Data
| Density | 117.5 | 188.0 |
188.0 – 117.5 / 117.5 x 100 = 60.0% percentage error
Yellow Birch
Actual Data
| Density | 108.9 | 76.0 |
76.0 – 108.9 / 108.9 x 100 = 30.2% percentage error
Chestnut Oak
Actual Data
| Density | 87.5 | 36.0 |
36.0 – 87.5 / 87.5 x 100 = 58.9% percentage error
Red Maple
Actual Data
| Density | 118.9 | 152.0 |
152.0 – 118.9 / 118.9 x 100 = 27.8% percentage error
Striped Maple
Actual Data
| Density | 17.5 | 20.0 |
20.0 – 17.5 / 17.5 x 100 = 14.3% percentage error
White Pine
Actual Data
| Density | 8.4 | 0.0 |
0.0 – 8.4 / 8.4 x 100 = 100% percentage error
