Mohn Mill Sampling

Mohn Mill community was selected for the virtual forest tutorial community sampling exercise to which area method was used in conjunction with systematic, random, and haphazard sampling techniques. There were 24 quadrats sampled for each.

The technique that was most efficient in time spent sampling was haphazard which took 12 hours and 18 minutes in comparison to 12 hours 35 minutes for systematic and 12 hours and 34 for random.

When comparing species densities actual versus estimated (data) the majority of species were found to have higher actual densities over estimated densities this included: White oak (actual – 74.5; Est. 36.0); Chestnut oak (actual – 82.9; est. – 72.0); Witch hazel (actual – 142.4; est. 40.0); Red/Black oak (actual – 46.7; est. 32.0); Eastern hemlock (actual – 45.6; est. 4.0); White pine (actual – 12.8; est. – 0.0); Downy juneberry (actual – 9.9; est. 8.0); Black cherry (actual – 1.5, est. 0.0); Sweet birch (actual – 1.2; est. – 0.0); and Yellow birch (actual – 0.8; est. 0.0). Only 6 species actual densities versus estimated (data) densities were lower: Red maple (actual – 403.7; est. – 404.0); Black tupelo (actual – 35.5; est. 40.0); Striped maple (actual – 13.6; est. 136.0); Hawthorn (actual – 4.5; est. 16.0); American basswood (actual – 1.5; est. – 4.0); and White ash (actual – 0.8; est. – 4.0). 

The most common species overall was Red maple (91.0% frequency) followed by Witch hazel (36.0% frequency), White oak (35.0% frequency), Chestnut oak (28.0% frequency), and Red/black oaks (24.0% frequency). The rarest species were Black cherry, Sweet birch, American basswood, Yellow birch, and White ash all of which were found at a 1.0% frequency. I only calculated the percentage error for Red maple (the most common species) and Yellow birch (one of the least common species). 

Sample Calculations for percentage error:

Systematic Sampling:

Most common species (highest frequency):

Red maple (404.0 – 403.7)/403.7*100 = 0.074%

Rarest species (lowest frequency): 

Yellow birch – (0.0-0.8)/0.8*100 = -100%

Random sampling:

Most common species:

Red maple – (362.5-403.7)/403.7*100 = -10.21%

Rarest species 

Yellow birch – (0.0-0.8)/0.8*100 = -100%

Haphazard sampling:

Most common species:

Red maple – (466.7-403.7)/403.7*100 = 15.61%

Rarest species:

Yellow birch – (0.0-0.8)/0.8*100 = -100%

The most accurate sampling strategy for common species appears to be systematic sampling. For the rarest species the percentage error did not change. The accuracy for rare species declined as the rare species numbers increased. To determine this I had to use another species that varied across the systematic, random, and haphazard sampling techniques to which I used Hawthorn. The percentage error calculations for Hawthorn are as follows: systematic – (16.0-4.5)/4.5*100 = 255.5%; random (4.2-4.5)/4.5*100 = -6.67%; and haphazard (20.8-4.5)/4.5*100 = 362.22%.  I feel like using more than 24 sample points would have been better considering that there were more values across the x axis than was used from the systematic sampling technique. Moreover, for haphazard sampling I used areas of high aggregation which most likely skewed my results. Areas of low aggregation potentially have species that were rare in areas of high aggregation.