Effects of Soil Erosion Barriers on Percent Cover and Sediment Size

Ranching began on Santa Rosa Island in the 1840’s, introducing nonnative megafauna that put selective grazing pressures on endemic species. Dense groves of island oak (Q. tomentella) are aid in sediment deposition and retention. A current restoration effort, involved installing soil erosion barriers, known as wattles, to prevent sediment from being lost upslope and recruit plant growth whose root systems could further stabilize the slope. This experiment was designed to compare percent cover of vegetation growth in areas with and without soil erosion barriers. This was done using the line intercept method (n=42) on three meter transects, measuring intervals along the transect where plant cover was present. At the end of the transect, the sum was calculated to determine percent plant cover. The results showed areas with soil erosion barriers had a higher average percent plant cover (24.5%) compared to areas lacking soil erosion barriers (10.2%). The experiment sought secondly to quantify the size of sediment in areas with and without soil erosion barriers (n = 42) on a slope in the middle of the island that contains a grove of Q. tomentella. On each transect where percent plant cover was measured, a sediment sample was taken. The sediment was weighed in grams, and run through a series of micron sieves. The sediment was weighed in grams, and the distribution was observed. After comparing the two treatments, there was no significant difference between the distribution of sediment sizes. This data informs future restoration attempts in their decision for placement of sediment retention devices. Future studies could focus on areas of the slope that would benefit most from soil erosion barrier devices. Additionally, many of the plants that were observed were nonnative grasses, and there could be investigations regarding how to allow endemic species to colonize these disturbed areas more successfully