Effects of manure and sawdust/sucrose amendments on soil quality, plant biodiversity, and plant density in urban riparian restoration

  Riparian ecosystems are a top priority for restoration because they support high biodiversity and contribute to a variety of valuable ecological services such as soil conservation, flood control, and water purification. This three year study utilizes two inexpensive and readily available treatments, manure and sawdust/sucrose amendments, to enhance restoration of a riparian habitat surrounding an urban lake. While these amendments are known to enhance restoration in old fields, sage scrub, and grassland ecosystems, their efficacy in restoring riparian systems has not been evaluated. In order to evaluate the efficacy of these amendments, forty experimental plots were established in summer 2005. Each plot was assessed for plant density, plant biodiversity and soil quality (measured as pH, nitrogen, potassium, phosphorus, and carbon) in summer 2005 and 2006. Between 2005 and 2006 a 27% decrease in total plant density and a 44% decrease in plant diversity were observed. The decrease in plant density did not alter the dominance of  native grasses (covering 64% of the study area), but a  41% density increase of  exotic Centaurea maculosa (spotted knapweed) and a 79% decrease of exotic Melilotus Alba (white sweet clover) were observed. This change in species density may be related to differences in nitrate, potassium, and phosphorus in manure and sawdust/sucrose amended plots. If these amendments are successful in changing the soil quality and favoring native plants, this low cost restorative technique could become a template for  municipalities to maintain and improve their urban resources.