Ongoing Field Observations along a Peninsula

As I’ve become more interested in GIS and erosion lately, I’ve been paying a lot of attention to both and will likely focus my observations on the active erosion occurring along the peninsula. I decided to pursue my first line of questioning from my previous blog post while visiting the site a second time, and paid close attention to the vegetation cover type in relation to the extent of erosion on the shoreline.

I’m not sure if there are any scientifically preferred methods of quantifying erosion at this scale, however for this study I think that measuring the height of unvegetated soil, beginning at the water’s surface and ending where the soil is stabilized by vegetation would be a good representative measure. A quantifier for “stabilized” will need to be fleshed out in the future before the big data collection occurs, perhaps something like “less than 25% exposed soil, by visual approximation” would do. But this might vary in it’s practical application between cover types such as grass and trees. Maybe poking a stick into the soil to evaluate the extent of the existing root networks would be a better quantifier for that. Or maybe, the angle of the slope would be a good inticator.

Anyways, my visual observations suggest that there are 3 distinct types of vegetation communities along the peninsula. The most common is grassland. Surprisingly, the peninsula and the shorelines leading up to it appear to be extensively covered with a wide variety of tallgrass prairie species such as big bluestem, little bluestem, blue grama, among others. There are also desiccated forbs of a very wide variety, although winter identification will be tough outside of the easily identifiable ones such as flodman’s thistle, closed gentian, milkweed, sunflowers, etc. This may be a rare surviving holdout of ultra-rare, original tall grass prairie. The next most common cover type is early successional aspen forest that is consuming the grassland. The trees are young looking, likely not more than 15 years old. There still exists much grass covering the ground within these aspen groves. These two cover types are constrained to the horizontal plateau of the peninsula, and remain several feet above the water’s surface along its length. A third cover type is sandbar willow, and this appears to be in early successional stage of taking over the grassland, however unlike the aspen trees the willow is predominantly established low along the shore where it likely seeded in, where is encroaching upward into the plateau cover types. There are areas of of both grassland and aspen grove on the plateau, with or without these willows present. It might be difficult to categorize these different combinations into only a few variables of study.

I think a good hypothesis to investigate is that the type of vegetation cover above the shoreline is related to the severity of shoreline erosion.

The response variable would be something like height of destabilized soil above the water’s edge, which would be a continuous variable. The explanatory variable would be the type of vegetation cover directly above that measured height, which would be categorical.

I made one rough observation roughly in the middle of a representative area of each cover type. Grassland had 1.5 metres of exposed soil under it, aspen forest 0.75m, sandbar willow with grassland had 0.25m, and aspen forest with with willow had 0.5.

The amount of aspen forest with sandbar willow is much lower than I remembered, so I might just drop that category. I suspect that sandbar willow offers the greatest erosion protection, followed aspen, followed by grassland. Further, I suspect that willow combined with aspen might prove superior to any of those categories, however there is not enough of this cover type on the peninsula to yield meaningful data.