Growth Response of Picea mariana Seedlings to Competition for Radiation
The growth response of 4-year-old black spruce seedlings (Picea mariana (Mill.) B.S.P.) to reduced radiation availability (DIFN) caused by herbaceous and woody competitors was investigated on a clay and on a loam site on a research plot in Ontario, Canada. Variability in black spruce growth was less explicable by reduced radiation availability caused by woody competitors than growth variability caused by herbaceous competitors. On the clay site, competition from fireweed (Epilobium angustifolium L.), Canada bluejoint grass (Calamagrostis canadensis (Michx.) Nutt.) and red raspberry (Rubus idaeus L. var. strigosus (Michx.) Maxim.) decreased black spruce diameter by more than 40% compared to seedlings without competition. Canada bluejoint grass and fireweed also distinctly reduced black spruce diameter performance on loam (> 30%). These results are discussed in relation to the need of vegetation control.