Growth and competition among understory plants varies with reclamation soil and fertilization

Abstract

Introduction: Following oil sands mining in Alberta, Canada, the main land management goal is to establish a functioning boreal forest ecosystem, including the understory plant community. One of the challenges with restoring the understory is the presence of non-native species that compete with desirable native species for resources. In a greenhouse experiment, we studied the growth of two native understory species (Galium boreale and Vicia americana) and a non-native invasive species (Matricaria perforata) grown with either intra- or interspecific neighbors across three common land reclamation soils and a nitrogen fertilizer treatment. Results: When grown by itself, V. americana aboveground biomass did not differ among soil or fertilizer treatments, likely due to its ability to fix nitrogen. Growth of M. perforata was directly related to soil nitrogen, and it had the greatest increase in biomass with fertilization. Growth and biomass of G. boreale was less than the other species, and it had the highest mortality in the nitrogen-poor soil. When grown together, the proportional biomass of M. perforata and V. americana varied with soil treatment such that M. perforata was dominant in the high-nitrogen forest floor-mineral mix treatment while V. americana was dominant in the low-nitrogen peat-mineral mix. Conclusions: Operationally, care should be taken when applying fertilizer to reclamation areas, as it may have an unwanted positive effect on growth for undesirable non-native plants at the expense of native species. In terms of seed mixtures, V. americana may be a good option for low inorganic nitrogen resource soils and G. boreale for high nitrogen resource soils.