In the virtual forest tutorial I used three sampling techniques (systematic, random, and subjective) using area-based methods. When using a systematic technique, I was able to sample five species of tree (eastern hemlock, sweet birch, yellow birch, chestnut oak, and red maple) which resulted in a diversity index of 1.4 and an estimated sample time of 12 hours and 36 minutes. When using a random technique, I sampled the same five species of trees as with the systematic technique, but the diversity index was lower at 1.1, and the sampling time was greater at 13 hours and 11 minutes. Finally, using a subjective technique, where I tried to sample an area covering the entire map at relatively equal distances in an attempt to discover more species, I sampled the five species of trees discovered previously in addition to two new species (striped maple and white pine), which resulted in a diversity index of 1.4 and a sampling time that was equal to the random technique.
Which technique had the fastest estimated sampling time?
The systematic technique had the fastest sampling time with a time that was 35 minutes faster than both the random and subjective techniques.
Compare the percentage error of the different strategies for the two most common and two rarest species.
Two most common species:
- Eastern Hemlock
- % error of systematic technique = (548.0 – 469.9)/469.9 x 100 = 16.62%
- % error of random technique = (620.0 – 469.9)/469.9 x 100 = 31.94%
- % error of subjective technique = (540.0 – 469.9)/469.9 x 100 = 14.92%
- Sweet Birch
- % error of systematic technique = (156.0 – 117.5)/117.5 x 100 = 32.77%
- % error of random technique = (124.0 – 117.5)/117.5 x 100 = 5.532%
- % error of subjective technique = (112.0 – 117.5)/117.5 x 100 = 4.681%
Two rarest species:
- Striped maple
- % error of systematic technique = (0.0 – 17.5)/17.5 x 100 = 100%
- % error of random technique = (0.0 – 17.5)/17.5 x 100 = 100%
- % error of subjective technique = (16.0 – 17.5)/17.5 x 100 = 8.57%
- White pine
- % error of systematic technique = (0.0 – 8.4)/8.4 x 100 = 100%
- % error of random technique = (0.0 – 8.4)/8.4 x 100 = 100%
- % error of subjective technique = (4.0 – 8.4)/8.4 x 100 = 52%
Did the accuracy change with species abundance?
Yes. The density estimates for species with greater abundance were generally much more accurate than for the species that were more rare. For example, the percent error values for the most abundant species (eastern hemlock) were between 14.92% and 31.94%, whereas the percent error values for the most rare species (white pine) were between 52% and 100%.
Was one sampling strategy more accurate than another?
Yes. Based on the percent error calculations, the subjective sampling technique was the most accurate technique (average percent error for all species of 16%), followed by the random sampling technique (average percent error for all species of 47%), and then the systematic sampling technique (average percent error for all species of 51%).
Below is a screenshot of my results of the virtual forest tutorial:
