Screening for control of a forest weed: early competition between three replacement species and Calamagrostis canadensis or Picea glauca.
In a growth chamber experiment, an additive series design was used to test the ability of 3 replacement species (Trifolium pratense, T. repens and Epilobium angustifolium) to suppress Calamagrostis canadensis, a problem species in the regeneration of Picea glauca in mixed-wood associations of the boreal forest. Effects of the replacement species on P. glauca seedlings were also tested. Seedlings of C. canadensis were planted at 3 different times (same time as, and 2 and 4 weeks later than the replacement species) into 4 densities of the replacement species (229, 601, 1577 and 4174 plants m-2). Seedlings of P. glauca were planted into the same 4 densities of the replacement species and at the same time as the replacement species. Light transmission through the replacement species' canopies decreased with time and increasing density. After 8 weeks, the deepest shade was cast by T. pratense, which reduced light transmission to as low as 4%. Biomass and mortality of the replacement species were not affected by C. canadensis or P. glauca. The replacement species did, however, show different rates of density-dependent mortality, which was attributable to different levels of intraspecific competition. Above-ground biomass accumulation, rhizome production and mortality in C. canadensis was negatively affected by all 3 replacement species, especially at the latest planting time. Height and biomass of P. glauca seedlings was also reduced by all replacement species. The results indicated that all 3 replacement species could be used to control seedling establishment by C. canadensis. Differences between the replacement species are discussed in the light of possible applications in forestry.