Negative Interactions between Tree Seedlings and Non-Native Grasses in a Restoration Setting: Getting to the Root of the Problem
Aldrovandi, M.  2018.  M.S. Thesis.

Abstract:
Aggressive herbaceous plants are often planted on reclaimed minesites, but these can inhibit the establishment of woody vegetation on the site. The objective of this study was to determine which of nine ground cover species [ragweed (Ambrosia artemisifolia), annual ryegrass (Lolium multiflorum), partridge pea (Chamaecrista fasciculata), black mustard (Brassica nigra), lablab (Lablab purpureus), sorghum (Sorghum bicolor), German millet (Setaria italica), smartweed (Polygonum pensylvanicum), sunn hemp (Crotalaria juncea)] would outcompete tall fescue without outcompeting shortleaf pine (Pinus echinata), chinkapin oak (Quercus muehlenbergii), and northern red oak (Quercus rubra) tree seedlings on a legacy mine site. It was predicted that groundcover species that do not have a shallow root system with an extensive surface area will be less competitive with tree seedlings than species that have a shallow root system with an extensive surface area. Competition was determined by tree growth, transpiration rate, and chlorophyll content over the period of about 1 year. Results from this experiment showed no significant effect on height or root collar diameter (RCD) growth by treatment or seedling species. There was no effect on transpiration rate or chlorophyll content by treatment. Some effect was found on transpiration rate and chlorophyll content by cover. Intermediate levels of groundcover were found to be the most beneficial. Despite treatment species being seeded at high rates, results did not indicate effective competition between treatments and the vegetation already present on site. Even if seeding rates were increased to outlandish levels, the cost of seed would outweigh any benefit that might exist.