Competition Between Herbaceous Vegetation and Conifer Seedlings on a Biosolids Amended Mine Site

摘要

A field-scale tree trial was established in 2013 and 2014 on rock disposal site slopes at the British Columbia Mount Polley Mine to evaluate various 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: a native grasses and forbs mix (at 5 kg/ha or 10 kg/ha), a native forbs mix, fireweed, or left unseeded. The control parcels were also left unseeded. Lodgepole pine, Douglas-fir, and native 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. The higher vegetative cover (in particular, graminoid cover) was associated with greater competition with conifer seedlings, increased vegetation/snow press, increased rodent damage to the trees and therefore reduced seedling survival rates. The growth of the conifers however, was notably higher on the parcels amended with biosolids as compared to the 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 rates while still providing erosion and invasive plant control.