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The main difficulty with my sampling strategy was to do with the site locations. Before I began sampling, I went out to the field and used coordinates to document the areas where there were cedar trees (Thuja plicata) and where there were other trees but no cedar trees present. I then listed off all the coordinates and used a random number generator to select five sites of each type to sample. I planned to walk a number of paces (also generated by a random number generator) from the tree closest to where my GPS said I had reached my destination. This location would be slightly different from where I had taken the coordinates due to GPS inaccuracies caused by the forest canopy (Ordonez Galan et al., 2011). However, I did not take into account the level of imprecision, likely also caused by the tree cover. Instead of taking me to a precise destination as it would in an open area, the GPS only took me to about 20 metres away from the endpoint. To get around this, I began counting my paces from the tree closest to when the GPS had the lowest number of metres left to go.
The surprising part of the data was that the highest value of biomass collected was from a site with Cedar trees. Sample 3 with Cedar trees had a biomass of 580 g/m2. This value was inconsistent with the rest of the data collected from sites with cedar trees and is 28 g/m2 more than the highest value of the samples without cedar trees. I have gone back to this site and suspect that there are some confounding variables at play here. These variables include the amount of sunlight and the topography of the site.
I will be changing my data collection technique to take these confounding variables into account. To do this, I will ensure that the sites I document with coordinates are not in direct sunlight and have relatively constant terrain (no divots where water could pool). I will then continue to use a random number generator to select the sample sites. Another change that I will be making is to begin taking moisture samples alongside the moss samples. I will choose a day to go out and take soil samples from all the sites. Afterwards, I will weigh them, let them dry out and then weigh them again to find the moisture content.
Bibliography:
Ordonez Galan,C., Rodriguez-Perez, J.R., Martinez Torres, J., & Garcia Nieto, P.J., (2011). Analysis of the influence of forest environments on the accuracy of GPS measurements by using genetic algorithms. ScienceDirect, 54(7-8), 1829-1834
The site with high moss cover adjacent to a cedar tree did it have high sunlight and what was the topography? How close to the tree are you taking your measurements? Make sure to include all the details of sample site selection in your final paper. Also, when you interpret your results in the discussion make sure you take into account how widely you could extrapolate your results if your samples are taken under certain conditions.