Blog Post 4: Sampling Strategies
In the virtual tutorial, I used the area-based method on the Snyder-Middleswarth Natural Area for this exercise with 20 plots were sampled for systemic and random sampling methods.
Which technique had the fastest estimated sampling time?
It looks like the systematic sampling method had the fastest estimated time due to the following:
- Systematic Sampling Method (10 Hours, 5 Minutes)
- Random Sampling (12 Hours, 10 Minutes)
- Haphazard Sampling (13 Hours, 30 Minutes)
Calculations
Most Popular
| Haphazard | Random | Systematic | |
| Eastern Hemlock | 404.0 – 469.9
469.9 * 100% = 0.4% |
482.6 – 469.9
469.9 * 100% = 2.7% |
455.0 – 469.9
469.9 * 100% = 3.17% |
| Yellow Birch | 140.0 – 108.9
108.9 * 100% = 28.55% |
– | 150.0 – 108.9
108.9 * 100% = 37.7% |
| Red Maple | – | 104.3 – 118.9
118.9 * 100% = 12.27% |
– |
Rare
| Haphazard | Random | Systematic | |
| Chest Nut Oak | 104.0 – 87.5
87.5 * 100% = 18.86% |
– | – |
| White Pine | 12.0 – 8.4
8.4 *100% = 42% |
13.0 – 8.4
8.4 * 100% = 54.76% |
5.0 – 8.4
8.4 * 100% = 40% |
| Stripped Maple |
– |
13.0 – 17.5
17.5 * 100% = 25.71% |
15.0 17.5
17.5 * 100% = 14% |
Systematic Sampling Method
Compare the percentage error of the different strategies for the two most common and two rarest species.
- Most common species – Eastern Hemlock and Yellow Birch
- Rarest species – Striped Maple and White Pine
Area-Based Method
- Total quadrats sampled: 20
- area sampled: 2000 sq. m.
- species sampled: 7
- Total specimens sampled: 165
Time Commitment
- Total quadrats sampled: 20 x 30 mins each = 600 mins
- Distance Traveled between Quadrants 309m @ 3mph = 60 mins
- Total time to sample: 10 hours 5 mins
Random Sampling Method
Compare the percentage error of the different strategies for the two most common and two rarest species.
- Most common species – Eastern Hemlock and Red Maple
- Rarest species – Striped Maple and White Pine
Area-Based Method
- Total quadrats sampled: 23
- area sampled: 2300 sq. m.
- species sampled: 7
- Total specimens sampled: 200
Time Commitment
- Total quadrats sampled: 23 x 30 mins each = 690 mins
- Distance Traveled between Quadrants 3220m @ 3mph = 40 mins
- Total time to sample: 12 hours 10 mins
Haphazard Sampling Method
Area-Based Method
- Total quadrats sampled: 25
- area sampled: 2500 sq. m.
- species sampled: 6
- Total specimens sampled: 223
Time Commitment
- Total quadrats sampled: 25 x 30 mins each = 750 mins
- Distance Traveled between Quadrants 4822m @ 3mph = 60 mins
- Total time to sample: 13 hours 30 mins
Percentage Errors
Percentage error is calculated as the absolute value of
(E – T) x 100%
T , where E = estimated value and T = true value
Which sampling strategy was more accurate than the other?
The percentage error results show that the random sampling method has a higher accuracy rate than systemic or haphazard sampling methods when we look at the percentages for common species.
But considering all four species, the systemic sampling strategy is much more accurate than the other techniques.
Did the accuracy change with species abundance?
After reviewing the percentage error of the 4 species, i.e., the two most common and two rarest species, the main factor influencing this percentage is the abundance rate between each species. In conclusion, based on the above data, accuracy diminishes with species’ rarity (the less abundant species are generally less accurately sampled).