The initial data collection showed some flaws in my strategy, and in my understanding. In noticing the relationship between the distance from the river and the gradient of biomass coverage I recognized far too many variables. I became a little lost. I tried to design an experiment to see how a certain variable related to the flow of the river affects the vegetation near the river. However in doing so I was overwhelmed with the realities of interconnectivity. The confounding variables I noticed include; the angle and composition of the ground at the river’s edge, the width and depth of the river at any given point, the rise and fall of the river seasonally, the amount of sunlight at the river’s edge etc. All these variables not only have a relationship to the vegetation along the edge, but also to one another.
The data I collected was not surprising. I found high biomass in patches. The river was wide, the water was flowing relatively slow, and the river is highest at this time of year.
I have decided to change my approach. I am going to study the relationship between the energy levels of the river and the density gradient of Gaultheria Shallon (salal). Instead of percent cover I am going to use a distant based measuring method.
The river is essentially going to be my transect and I will be using a random number generator to determine the strides between each measurement.
I am going to categorize the energy level into low or high based primarily on sedimentation; this is my predictor variable. For my response variable I will be measuring the closest Gaultheria Shallon plant from the river and the distance to the 3 closest Gaultheria from the initial measured plant. I am going to repeat this measurement with a starting point 3m up from the river. This data is going to be used to calculate density.
I think this will improve my study as I realized I was trying to categorize the energy level, and the presence of sediment is more a predictor of energy than the location on a bend. I also believe that the density of Gaultheria is a better indicator of the progression from bare substrate to forest ecology than general biomass. I still will have to acknowledge the confounding variables such as the increased sunlight at the rivers edge.
It sounds like you have learned the lessons of many field biologists, there are so many variables and many of them are interconnected and may be hard to measure! I think you have narrowed your study down well and focusing on one specific plant distribution is a great idea. I’m not sure I completely understand your sampling strategy in terms of where you will start and end, this will probably be more clear in your small assignment. I like the distance based measurement to the closest salal. You could still consider doing density by by doing a 5 – 10 m radius plot around that first plant though I think the way you have described works as well. Your small assignment should also include how you are going to characterize sedimentation.
I totally get feeling overwhelmed with how interconnected everything is and just how many points of data you can collect. This seems a lot more manageable and potentially quite informative. Using the river as your transect is a nice touch too, moving through the forest and keeping your transect strait is a bit of a headache.
Would plant roots also be a potential confounding variable regarding sediment? If the water gets high only occasionally there might be areas that keep it if there’s roots but don’t if there aren’t roots.