In our first week on the Spring Creek preserve I noticed a strange pattern: Along the hillsides near our camp there were a series of horizontal vegetation bands, alternating between relatively sparse and dense vegetation. I immediately began to question why this was happening. My conclusion was that, since the bands occurred along the strike of the bedding, there had to be a difference in the underlying bedrock which would make some layers more suitable to plant growth than others. And since access to water is one of the main limiting factors for growth on the preserve, I decided the difference had to be in porosity.
Three weeks later, I set out to test my theory. I would map the plant communities within each of the bands to quantify the difference in growth and determine whether any unique communities had arose from this phenomenon, then I would dig a hole at each site mapped down to bedrock and measure the porosity. I quickly ran into a problem which turned my testing on its head: The Mowry formation, where these bands were observed, is made entirely of shale. There are two important things to know about shale porosity; One, that shale rock is hardly porous at all – the grains form too tightly to leave channels for water to flow into the rock, and two, that shale formations are extremely porous, because of the way they tend to form in thin, loosely connected beds, leaving ample room for water to flow through. The porosity of shale formations has been well studied by people with million dollar scanners, but it would be impossible to measure with the materials I had available.
I changed my hypothesis. Instead of measuring porosity, I would instead measure bedding thickness and induration, which is how difficult it is to break apart. My theory was that plants would have less resistance growing their roots through thinner, less indurated beds, thus more plants would grow in those layers out of opportunity. Though I haven’t analyzed the data yet, it does seem like the general trend supports this new hypothesis, but there are a few outliers I need to find a way to explain, such as one relatively dry layer with thinner bedding than the surrounding layers, or another layer with very little vegetation despite having deep topsoil. All in all I am happy with the data I collected and excited to present it.
