5 – Reflections on study design

My sampling strategy was to use a 12m measuring rope to count the number of big sagebrush and green rabbitbrush along the hillsides coming up from Guerin Creek. I counted the number of plants within a 3m segment of rope, extending 0.5m on either side of the rope to give a 3m2 quadrat.

Sampling this number of quadrats was very doable, in total there were 8 unique lines measured and bushes counted and it took one hour. In implementing my sampling strategy, a few things went differently than planned. First, I misjudged the depth of the creek valley, so ended up with double the distance I was expecting to cover. My rope wasn’t designed for more than 12m of measurement, so I only measured the initial 12m as planned, and then counted bushes from an elevation of 12m to the top of the hillside. Additionally, there were between 15-30cm of snow cover, depending on the hillside. This prevented the counting of any young bushes, therefore only mature bushes grater than 40cm high were included in the count.

The data I collected was close to what I expected after doing some research (table 1). The intital 3m are likely flooded in the spring, and so there were few established brush plants right creekside. The number of plants actually then increased all the way to 12m, so clearly they are able to germinate and grow that far from the water table. However, there were 6.67 sagebrush plants per m between 9-12m; while from 12-45m there were only 1.13 bushes per m. When I take another sample I will include measures from 12-18m, 18-24m, 24-30m and 30-36m from the creekbed. This will help elucidate more information about how far above the water table the bushes thrive. Rabbitbrush is much less frequent on the hillsides, so it’s accuracy may not be as good as the big sagebrush measures.

I will need to sample around the entire creek, since there were significant differences between the topography of the two hillsides. The bushes in the second site were nearly double the size and the hillside was very steep compared to Site 1.

Table 1. Mean number of sagebrush and rabbitbrush bushes counted at various elevations from the Guerin Creek bed at Thompson Rivers University in Kamloops, BC.