Understory species and functional diversity in a chronosequence of jack pine and red pine stands in the south-central boreal forest

Abstract

Dominant tree species and anthropogenic disturbances influence understory taxonomic diversity (TD) and species traits (functional diversity, FD) in managed forests. We compared understory TD and FD in managed jack pine (Pinus banksiana Lamb.) stands and red pine (Pinus resinosa Ait.) plantations. Understory herbs, grasses, shrubs, and nonvascular species were assessed in 1 m2 quadrats on two perpendicular line transects. Data were analyzed using generalised least squares regression, and multivariate fourth corner and RLQ analyses. Although there were few differences in understory species communities, red pine plantations appeared to impose weak environmental filters on TD in ways that were absent from the jack pine stands. Taxonomic diversity declined with age in red pine but not in jack pine, and may have been affected by the accumulation of litter cover in red pine stands. Although vegetation cover was lower in red pine than in jack pine, species richness on a percent cover basis was greater, and saturated at high cover levels in jack pine. Functional richness and evenness were unaffected by overstory species, but high litter cover favoured higher values of functional divergence. These results imply that there was a high level of functional redundancy among species for the suite of traits that we analyzed.