User: | Open Learning Faculty Member:
Three sampling methods were used in gathering data from the Mohn Mill community using the virtual forest tutorial: haphazard, random, and systematic.
An equal number of quadrats were sampled (i.e. 30 each) with the systematic sampling technique having the fastest sampling time but, the sampling time for all three methods remained within the range of 15 to 16 hours. The haphazard method had a sampling time of 15 hours and 57 minutes, and the random sampling method has a sample time of 15 hours and 49 minutes.
In all three sampling strategies, Red Maple and White Oak were determined to be the two most common species; However, the results for the two rarest species differed for each method (i.e. American Basswood, Sweet Birch, White Ash, and Hawthorn).
- Haphazard or convenience sampling
Using the area, haphazard sampling technique for the Mohn Mill community, American basswood and Hawthorn were the two rarest species as indicated by the actual importance value.
| · Hawthorn
Actual importance value: 0.6
Calculated importance value: 0.4
|
· Sweet birch
Actual importance value: 0.2
Calculated importance value: 0.7
|
- Random sampling
Using the area, random sampling technique for the Mohn Mill community, White ash and Hawthorn were the two rarest species as indicated by the actual importance value.
| · White Ash
Actual importance value: 0.2
Calculated importance value: 0.6
|
· Hawthorn
Actual importance value: 0.6
Calculated importance value: 0.6
|
- Systematic sampling
Using the area, systematic sampling technique for the Mohn Mill community, American basswood and Sweet birch were the two rarest species as indicated by the actual importance value.
| · American basswood:
Actual importance value: 0.2
Calculated importance value: 1.5
|
· Sweet birch:
Actual importance value: 0.2
Calculated importance value: 0.7
|
For all three sampling methods—haphazard, random, and systematic sampling—the accuracy improved with abundance.
Of the three methods, the random sampling method had the highest accuracy.
I found it interesting that the systematic method of sampling had skewed the density of the rare species to such a substantial extent, making a haphazard sampling approach appear to be a more desirable sampling method. I was also surprised to see haphazard having the degree of accuracy it did.
A reason for the lack of accuracy using the systematic sampling method could potentially be using a transect sampling method in conjunction with the systematic method. I selected the samples at regular distances along the transect, with the initial point randomly chosen. As stated in “Tutorial: Sampling techniques,” systematic sampling can produce problems if the points correspond to an underlying environmental pattern, which perhaps is the case for Mohn Mill community.
I am curious about the results stratified sampling and transects would obtain. For stratified sampling, the tree population would be split into somewhat homogenous groups (same species). I predict the accuracy for stratified sampling would be equivalent to, if not better than, the accuracy of random sampling and that the common species determined would match. I think stratified sampling would determine the rarest species to be Hawthorn and Sweet birch due to their occurrence in two of sampling methods used.
A method I am aware of that is commonly used in the forestry industry is the point-centered quarter method, where a point in the center of the forest is identified and then the area surrounding it is separated into four quarters. I am surprised this method was not within the tutorial given its common use in relation to trees. I’d be interested in seeing how the method compares to those used within the tutorial in terms of the rare species determined and accuracy.
