I plan to study two types of trees, one with a high water intake, and the other with a low water intake. These two species will be bur oak and black spruce pine trees. I will observe the plant species that surround the trees within 100 inches from the base of the trees.
My hypothesis is that the amount of water available to the plants surrounding the trees will impact the density and abundance of species that surround them.
The response variable is the difference in small plant species surrounding the two types of trees, and potential explanatory variable is the water availability to those small plant species. 
Hi Sarah,
Your your hypothesis seems clear and understandable. The potential response and explanatory variables seem fairly easily measurable. Will you be distinguishing the species of plants around the trees into water/loving or drought resistant categories? Are you not distinguishing types of species surrounding the trees but only abundance of any kind?