User: | Open Learning Faculty Member:
While implementing my sampling strategy, some difficulties arose when deciding how to ensure randomization when selecting which sample units to measure. I needed to find a sampling method that allowed me to randomly choose a plant by assigning numerical values to put into a random number generator. I originally wanted to divide each strata into a grid of coordinates, but found out quickly that this was not feasible. I found it difficult to make a grid small enough that each box contained only one stem, therefore, I ended up using the distance-based method. I then found that as I was measuring the distances to the selected point, the plants were not fixed in space and so it was difficult to accurately select the correct plant. I then decided to place the measuring tape on the ground and measure to the bottom of the stem to ensure accuracy.
I found some of the data collected to be surprising, especially in the low degree of sunlight exposure strata. What surprised me was the degree of variation within these strata, especially that of the low degree strata. In this area, most of the plants were under 90 cm tall but there were a few that reached almost 110 cm. Because of this, I decided that five replicates was not enough data to accurately represent the population in each strata. I plan to continue to use the distance-based sampling method with the random number generator, but will generate more replicates so that I have a total of 10 sample unit measurements in total for each strata. I think that increasing the sample size will better represent the sample and decreases the variance within each strata.
Edit:
I decided to revise my research study, and focus on density of the Canada goldenrod as my response variable. I believe density is a better representation for plant growth success, as it eliminates other factors. Height would not be an accurate representation of plant success, unless I measured plant growth over a period of time. Due to the time constraints of my study, I would not be able to record meaningful data for differential plant growth among goldenrod plants in the different strata. As such, I have revised my study design and sampling methods to measure goldenrod density at different levels of sunlight exposure. To calculate density, I will use a stratified random quadrat sampling method, using the same strata that I initially identified. I will divide my study area into three 10 m by 10 m strata, representing low, moderate, and high levels of sunlight exposure. I will randomly place 10 quadrats in each strata by using a random number generator to generate two coordinates. I will continue generating coordinates until I have 10 points in each stratum. I will then locate these points on my study plot by placing a measuring tape on the ground and measuring the appropriate point, which will represent the bottom left-hand corner of the quadrat.
