Effects of logging disturbance on understory plant communities in temperate forests.

Abstract

A meta-analysis of 39 empirical studies quantifying understory plant species richness in logged and unlogged temperate forests demonstrates lower species richness of shade-tolerant, forest species and vernal herbs in clear-cut forests compared to unlogged forests. In clear-cut forests, higher species richness of resident species and early sucessional and exotic species was found compared to unlogged forests. Silvicultural site preparation following logging decreased resident species richness and increased total species richness in logged forests compared to unlogged. Selectively logged forests support higher species richness of both resident species and all species compared to unlogged forest. A field study of selectively-logged, sustainably-certified, mesic forests on the Menominee Indian Reservation in Wisconsin demonstrated higher species richness in small gaps than in unlogged and undisturbed areas within the same stands. However, species richness per stand and per stem did not differ between logging treatments, indicating that low-impact selective logging alters the herbaceous species density without changing richness or composition within stands. The effects of selective logging were similar to published effects of natural disturbances. The importance of physical disturbance and altered environmental conditions after clear-cut logging for survival, growth and reproduction of a forest understory plant, <italic>Uvularia grandiflora </italic>, were experimentally tested in recently clear-cut and unlogged sites. Soil disturbance and slash deposition, significantly reduced <italic>U. grandiflora </italic> populations. The effects of a recently clear-cut environment varied with site conditions; on the most mesic site, <italic>U. grandiflora</italic> recovered to match control plots following logging. On drier sites, the opposite results were observed. These findings indicate that the response of <italic> U. grandiflora</italic> to logging varies with site conditions and that understanding response to logging by understory species requires incorporation of environmental variability. A seed dispersal and predation experiment, using seeds of <italic> U. grandiflora, Sanguinaria canadensis</italic> and <italic>Trillium grandiflorum </italic>, revealed few differences in rates of seed dispersal or seed predation among recently clear-cut forests, older clear-cut forests (15--20 years post-logging), and mature, unlogged forests, with the exception of higher rates of dispersal and predation of <italic>U. grandiflora</italic> seeds in recent clear-cuts compared to other logging treatments. Overall, however, results do not support the hypothesis that logging disrupts myrmecochory.