Effects of harvesting and deer browsing on attributes of understory plants in northern hardwood forests, Upper Michigan, USA

Abstract

Both forest harvesting and browsing by white-tailed deer ( Odocoileus virginianus Zimmerman) affect the composition and structure of forest vegetation throughout the eastern deciduous forest in the United States. We studied their affect and their interaction by measuring the composition, richness, cover, physical stature, and reproductive potential of vascular plants in the understory of three thinned (uneven-aged, even-aged, managing for old-growth characteristics) and two unthinned (second-growth, old-growth) forests dominated by sugar maple ( Acer saccharum Marsh.) in western Upper Michigan. Based on measurements taken five years after deer exclosures were established, we found consistent and strong statistical differences in species richness and percent cover related to forest harvest but not to deer browse. Percent cover of the understory vegetation showed weakly significant interactions between deer browse and forest harvest. Thinned forests had a greater average richness and cover of graminoid species, average cover of wild red raspberry ( Rubus strigosus L.) and sugar maple compared to unthinned forests. Measurements of plant morphology and the frequency of flowering and fruiting were more sensitive indicators of deer browse than community measurements such as richness and cover. Based on measures of physical stature and reproductive potential, sugar maple, red-berried elder ( Sambucus racemosa L.), bluebead-lily ( Clintonia borealis (Aiton) Raf.), small Solomon-seal ( Polygonatum pubescens (Willd.) Pursh.), false Solomon-seal ( Smilacina racemosa (L.) Desf.), rosy twisted stalk ( Streptopus roseus Michaux), and trillium species ( Trillium grandiflorum (Michaux) Salisb. and T. cernuum L.) all experienced significant browse damage. A better understanding of the interaction between forest harvest and deer browse and their effect on community composition and structure is critical to maintaining and enhancing biodiversity in managed northern hardwood forests.