Understory herb assemblages 25 and 60 years after clearcutting of a northern hardwood forest, USA

The abundance of understory herbs in 25- and 60-year old clearcuts was compared to adjacent old secondary stands to infer how herb assemblages change in space and time following clearcutting of secondary forest. Herb densities and environmental conditions were sampled along 100 m transects crossing the clearcut/old secondary forest boundary, at three sites with 25-year old clearcuts and three sites with 60-year old clearcuts. At the 25-year sites, species densities of the 23 most frequent species were compared between clearcuts and adjacent old secondary forest to classify species into response groups. Species were classed as “insensitive” if there was little or no difference in density (seven species), “sensitive” if densities were lower in the clearcuts (six species), “enhanced” if densities were higher in clearcuts (four species), and “edge-enhanced” if densities were highest near clearcut edges (six species). Densities of two of the six sensitive species declined significantly with distance from the edge into the clearcut. Further, when regression results for all 23 species were combined, the mean slope of density vs. distance was significantly negative, indicating an overall trend to lower density with distance into the clearcuts. Most species classed as sensitive at 25 years did not show similar sensitivity at the 60-year sites; only one species had lower density in 60-year clearcuts than adjacent old secondary stands. Overall, there were substantial residual effects of clearcutting on herb assemblages within 50 m of the historical edge at 25-year sites, but not at 60-year sites. This difference may be due to different logging practices at the two historical times, as well as the difference in time for recovery since logging.