Effects of conifer release with glyphosate on summer forage abundance for deer in Maine

Effects of conifer release with glyphosate on summer forage availability for large herbivores in northern forests have received relatively little study. We determined effects of glyphosate treatment of clearcuts on abundance of summer foods for white-tailed deer (Odocoileus virginianus) at 1 and 7-10 years posttreatment. We measured the abundance (percent cover in a 0- to 1.8-m height stratum) of five forage classes for deer (leaves of deciduous trees, leaves of deciduous shrubs, forbs, grasses, ferns) on 12 clearcuts (six treated, six untreated) to determine 1-year effects and on 10 clearcuts (five treated, five untreated) to determine 7- to 10-year effects. Abundance of leaves of deciduous trees was greater on untreated sites (38 versus 11%) at 1 year posttreatment, but the difference was less (18 versus 12%) at 7-10 years posttreatment (age x treatment interaction, P = 0.005). Leaves of deciduous shrubs exhibited a similar pattern. Abundance of forbs was similar (13-14%) at 1 year posttreatment but greater on treated sites (29 versus 15%) at 7-10 years posttreatment (P = 0.03). Grasses and ferns were less abundant than other forage classes. Overall, glyphosate application initially decreased the abundance of leaves of deciduous trees and shrubs used as food in summer, but the longer term positive effects on forb abundance may result in little net change in overall habitat value.