My hypothesis is that my object of study is more abundant in some areas than others because of differences in soil moisture content across the environmental gradient.
The initial set of field data compared plant height (response variable) to approximate soil moisture content (predictor variable).
I used a haphazard sampling strategy, alternating between measuring plants on the north and south sides of the path that runs through the site.
Since my response variable was plant height, the sampling unit was an individual plant.
There were no difficulties with the execution of the sampling strategy, but a couple of confounding factors made it difficult to ensure that a representative sampling occurred.
Firstly, the plant’s presence and abundance are patchy and uneven across the east-west transect (parallel to the path). With the marsh lying south of the path and the grasslands area north of it, I may need more than one north-south transect to collect representative data across the environmental gradient.
Secondly, a few consecutive days of on-and-off rain showers made the ground soft and moist. This made it easier to insert the moisture meter probes, but likely gave a falsely high moisture rating for some measurements.
The data was not very surprising, although there was some variation in height (68 cm to 34 cm) even though all samples were rated as having very wet soil.
Other issues:
- Drier conditions should reduce the potential for falsely high moisture ratings but could also make it difficult to insert moisture meter probes.
- The moisture meter is not very accurate – it merely rates soil conditions from 1 to 10 to indicate whether soil is dry, moist or wet. Obviously, a quantitative measure of soil moisture would be preferable, but I am not equipped to do that.
- There are many confounding variables, including other soil conditions like pH and salinity. Since I am not equipped to measure them, I will just have to account for them in the final report.
I will modify my data collection technique to a more systematic approach of measuring samples along a north-south transect. This will improve my research by providing more samples across a larger area, covering the full north-south range of the organism.