Data Collection: Tree composition differences within the forest and along the river

Before I set out to collect data I wanted to solidify my study design. I was not feeling confident and every plan I had seemed to be debunked by confounding factors. I realized that measuring the distance to the closest salal had far too many confounding variables as the geological and biological composition of the river’s edges varies significantly. What I did notice on my subsequent visits is the presence of many submerged trees. Since the water is much higher at this time of year than its summer lows I began to think about how these trees are affected by the magnitude of force coming down the river. I decided to measure the speed of the river and the presence or absence of submerged trees. I also am collecting data on the composition of trees near the river and the composition of trees 40m within the forest canopy. I chose to focus on trees because they are less impacted by changes in topography than salal and there are trees present everywhere in my study area along this river. 

I collected data yesterday by walking along the river and systematically taking measurements every 50m. I measured the speed of the water with a meter long pvc rectangle with a ping pong ball attached to a fishing line on one edge and a stopwatch. I measured the speed of the river 0.5m from the edge of the water three times and then calculated the average. Since the river speed varies in quick succession I marked the presence or absence of submerged trees within a 3m radius. I classified “submerged” as having any portion of the trunk touching the water. This river varies drastically with the rain and since the water is not at its highest, if any portion is touching the water now it is likely that the entire base of the trunk would be submerged when levels are high. I then identified all the trees within a 10x10m plot. I repeated this 6 times along one side of the river, crossed and repeated on the other side 6 times. After these replicates were measured I headed into the forest perpendicular to the river between 40-50m and identified all the trees. From here I moved parallel to the river 50m and repeated the identification process. I totaled 12 replicates so far of water speed and submerged trees, 12 replicates of near river tree species richness, and 12 replicates of in forest tree species richness.  

Issues implementing my sampling design come from the fact that it is late winter, almost spring and all of the deciduous trees still lack living leaves. I was still able to identify all accurately as most of them had remaining reproductive structures as well as build up of leaf litter remaining below. It also is rough terrain near the river however I was able to measure at all of my systematic points. 

I noticed that there were many submerged trees, even when the flow of water was measured to be relatively fast, some of which were growing at an angle almost parallel to the flow of the river. This made me think that a better correlation would be to measure the angle of the tree at each of these sites. The submerged trees were primarily Maples with a couple Black cottonwood and one large cedar in an area of very slow flowing water. I think that with the variation of water speed depending on complex water flow dynamics, the measurement of speed that I am doing is rather crude. I may decide to focus my efforts on documenting the composition of trees in various locations.