Conifer seedling establishment on a rock disposal site at the Mount Polley Mine to assess competitive effects of various herbaceous groundcovers when using biosolids as a soil amendment Hunt, Janelle; Holmes, Gabriel; McMahen, Katie
A field-scale tree trial was established in 2013 and 2014 on rock disposal site slopes at Mount Polley Mine to evaluate herbaceous groundcovers’ ability to promote coniferous tree growth on parcels amended with biosolids. Parcels were amended with 20 cm of overburden and biosolids were applied at a rate of 110 dry tonnes per hectare (control parcels received no biosolids). The parcels were then seeded with either: native grasses and forbs (at 5 kg/ha or 10 kg/ha), native forbs, fireweed, or unseeded. The control parcels were also unseeded. Lodgepole pine, Douglas-fir, and deciduous tree and shrub seedlings were planted across all parcels. After two and three growing seasons, herbaceous vegetative cover was highest on parcels seeded with native grasses and lowest on the forbs, fireweed, and unseeded parcels. Higher cover was associated with greater competition with conifer seedlings, increased vegetation/snow press, increased herbivory and reduced seedling survival. Growth of the conifers however, was higher on the parcels amended with biosolids compared to control parcels. These results suggest that the understory on biosolids amended soils should be seeded at low seeding rates with native forbs in order to have the highest conifer survival while still providing erosion and invasive plant control.
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