Effects of forest plantation management on herbaceous-layer composition and diversity

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Abstract
I compared the species composition and diversity of vascular plants in the herbaceous layer from a chronosequence of intensively managed spruce (Picea) plantations in three age-classes (5–7, 10–12, 14–16 years) with natural, mature stands (ca. 90 years) in southeastern New Brunswick, Canada. Total species richness (stand level) averaged 81–84 species in the three plantation age-classes compared with 64 species in the natural stands; richness of forest habitat species alone was 33–36 in the plantations and 37 in the natural stands. More fertile sites had significantly higher values for Hill's diversity indices (N0, N1, N2). Mean N0, N1, and N2 (subplot level) did not differ among stand types for all species, but N1 and N2 were significantly greater in the natural stands than in one or two plantation age-classes for forest habitat species alone. The two younger age-classes of plantations differed significantly in composition from the natural stands and the plantations became slightly more similar (Sørensen's index) to the natural stands with increasing age. One forest habitat species was lost and 24 others decreased in cover in the plantations. Tracking of plantations over a longer time period will be needed to determine whether these forest habitat species eventually regain their former abundance.Key words: chronosequence, forest harvesting, herbaceous layer, plantations, species diversity, species composition.