Mound microsites: Can they influence plant survival and growth in mine reclamation

This study examined arctic lupine (Lupinus arctica) and Mackenzie willow (Salix prolixa) seedling as well as growing medium responses to the effects of microtopography created by mounding the surface of a waste rock storage facility of a former metal mine in northern British Columbia. In the first two growing seasons of the study, mounding had a significant effect on near surface moisture (p<0.001), with moisture in the bottom swales measured to be significantly wetter than the other microtopographical positions, due to the accumulation of water. There were no measured effects on near-surface overburden temperature. The microtopographical treatments significantly affected the concentration of some nutrients, resulting in higher levels in the bottom swales likely due to nutrient leaching and displacement from locations on the mound. Overall plant survival was relatively high, with 5-year survival rates of 81% and 97% respectively for lupine and willow. Both willow and lupine seedlings exhibited highest mortality in bottom swales. Factors that may have contributed to higher mortality rates in the bottom swales include elevated moisture and concentrations of some metals and nutrients as well as reduced root lengths. Lupine cover, biomass and Rhizobium nodule formation were also significantly lower on plants occurring in the bottom swales. Similarly, after the first year of growth, willows planted in the bottom swales experienced the lowest cover and shortest root length in comparison to willows planted on the other mound locations. However, after the second year of growth, the highest cover was measured in willow plants occurring in the bottom swales. In this study, the microtopography formed by mounding the waste rock storage facility of a former metal mine facilitated significant differences in physical, chemical, and biological microsite conditions as well as plant survival and growth, at least in the first few years after planting. The created microtopography of mounding may be an efficient tool in influencing overburden characteristics and increasing the diversity of colonizing plant species on a mine reclamation site by providing a variety of sites favorable for seedling development.