User: | Open Learning Faculty Member:
I have selected the western redcedar tree (Thuja plicata) as the organism that I plan to study. The three locations along the environmental gradient in my research area are divided by the kind of soil the plants are growing in, namely sandy, silty and loamy soil (see field notes attached)
If a large population of cedar trees are observed thriving in silty soil but are entirely absent from areas with only sand, then western redcedars must need the moisture and nutrients that silty soil contains to populate an area successfully when in competition with pines and firs.
My hypothesis is that western redcedar trees grow in low elevation areas that collect moisture in silty soil. Therefore, because the distribution of western redcedar trees changes along the length of the research area, I predict that the composition of the soil varies as well, in a way that is either detrimental or beneficial to the growth of the tree in relation to the amount of water it can retain.
The response variable is the number of western redcedar trees observed in an area (density), which is a continuous variable. Some predictor variables are the slope, elevation, and soil that the trees grow in, all of which are related to the amount of moisture and nutrients available to the plant. Slope and elevation are continuous variables, but soil can be separated into sandy, silty or loamy soil, and is therefore categorical.
I like your definitions of your predictor variables. Do you have the methods to test the soil? It would be particularly interesting to see if your hypothesis of the difference in soil types/nutrients! Will you test the soil or rely on easier variables such as slope and elevation?
Sounds like a great project!
Your prediction is clearly stated but one potential confounding variable that first came to mind was aspect. Your notes show that aspect was noted so I assumed that you factored it into your research.