Hardwood Bark Chips as a Surfacing Material for Recreation Trails

Medium and coarse grades of central states hardwood bark chips were used in this experiment. A 24 by 36 inch Kinesko lawn roller was modified by welding 1-7/8 inch outside diameter galvanized pipe spaced on 4 inch centers around the outside of the roller. With a total weight of 540 lbs., applying 8 psi over the length of each pipe, each pass with the roller provided the equivalent of 18.75 people traversing the area. Sixty 3 foot by 5 foot plots were laid out in three replications of four compaction treatments with five bark treatments per compaction treatment. The bark treatments consisted of: a) 4-inch thickness of coarse grade bark, b) 4-inch thickness of medium grade bark, c) 2-inch thickness of coarse grade bark, d) 2-inch thickness of medium grade bark, and e) control (no bark). Compaction treatments consisted of: a) heavy use- approximately 265 people per day, b) medium use- 130 people per day, c) light use- 40 people per day, and d) control (no use). This was accomplished by making 14, seven, and two passes with the roller per day over the bark treatments respectively. Soil samples were taken with a Uhland soil core sampler every 2 weeks for a period of 12 weeks, one from each of the sixty plots. One inch of water was applied with an overhead rotary irrigation system to the entire plot area 24 hours prior to sampling. From these soil samples, the following determinations were made: a) soil moisture content, b) aeration porosity percentage, and c) bulk density. The hardwood bark surface provided protection for the trails as evidenced by the increased soil moisture percentage and reduced bulk density as compared to the control treatment. A 4-inch depth of medium grade, bark provided the most site protection, and the 2-inch depth of coarse bark provided the least protection. In general, the medium grade bark was better than the coarse grade bark in providing site protection. Aeration porosity percentage appeared to be a poor indicator of site protection.

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