In October 2018, 1.5 years after the mulching and trenching treatment, we surveyed tree and shrub regeneration using 1/500th of an acre (5.3 ft.) fixed radius plots. Data was collected in 36 plots, with 18 plots in the mulched and trenched two acres and 18 plots in the trenched two acres. The species sampled were buckthorn, red pine, aspen, pin oak, bur oak, cherry, hackberry, elm, ash, Rubus spp. (raspberry and blackberry), hazel, prickly ash, and amur maple. Any other species were grouped together as “miscellaneous native shrubs.” For pin oak and bur oak, separate counts were maintained for stump sprouts versus seed origin.
Overall, there was lower shrub density and higher tree density in the mulched and trenched treatment area compared to the trenched treatment area (Table 1, Supplemental Content). Buckthorn, hazel, and raspberry all had greater average density and height in the trenched treatment area compared to the mulched and trenched treatment area, suggesting mulching can help set back shrub growth. However, prickly ash height and density remained similar across both treatments and was slightly higher in the mulched and trenched area.
Both treatments resulted in considerable buckthorn density, with 12,000 stems per acre (22% relative density) in the mulched and trenched treatment area and 18,139 stems per acre (27% relative density) in the trenched treatment area (Table 1). These results suggest mulching and trenching can set back shrub growth better than just trenching alone. However, buckthorn still grows aggressively in each treatment, so mulching even when combined with disc trenching does not adequately control buckthorn.
Tree density was higher in the mulched and trenched treatment, with 7,167 trees per acre compared to 3,667 trees per acre in the trenched area. Trees in the trenched treatment were an average of 0.7 ft. taller than trees in the mulched and trenched treatment (Table 1). This difference in density and height might be attributed to the slightly older age of natural regeneration in the trenched-only treatment. Untrenched strips could have contained advance regeneration that was taller in height.
Looking at target species, red pine was originally planted at a density of 900 seedlings per acre. A year and a half post-treatment, there are 722 trees per acre of red pine occurring at 83% frequency in the mulched and trenched treatment and 222 trees per acre occurring at 33% frequency in the trenched site (Table 1). The difference in red pine density between each treatment suggests that the mulching treatment benefitted planted red pine seedlings, which was an unexpected result. This could also have to do with the regeneration plot size (5.3 foot radius) being smaller than the distance between rows and seedlings (7 feet). Pin oak density was fairly constant across both treatments, while bur oak density was nearly three times higher in the mulched and trenched treatment. Mulching combined with trenching appears to have suppressed competition enough to allow planted red pine, and to a lesser extent bur oak, to establish successfully.