WINTER FORAGING ECOLOGY OF MOOSE ON GLYPHOSATE-TREATED CLEARCUTS IN MAINE

The herbicide glyphosate is widely used in northern coniferous forests of the United States and Canada to promote conifer dominance on clear cut sites by suppressing regeneration of deciduous species. We determi ned effects of glyphosate treatment of regenerating clearcuts on (1) b rowse availability (total biomass, by species, and proportion with hig h digestible energy [DE] content), (2) browse use, and (3) diet qualit y of moose (Alces alces) in winter in Maine during 2 periods: 1-2 and 7-11 years posttreatment. We measured browse availability and use and collected browse samples for nutritional analyses on 12 clearcuts in J anuary-March 1991 before aerial treatment with glyphosate of 6 of thes e clearcuts in August 1991. We conducted posttreatment sampling of tre ated and untreated clearcuts during January-March 1992 and 1993. We al so sampled 14 clearcuts that had been treated with glyphosate 7-11 yea rs earlier and 5 untreated clearcuts of similar age in January-March 1 992 or 1993. Available biomass (kg/ha) of deciduous browse decreased ( P = 0.001) 70% on treated clearcuts relative to untreated clearcuts fr om pretreatment to year 2, but was not affected (P = 0.29) at 7-11 yea rs posttreatment. Available browse from red maple (Acer rubrum) and pa per birch (Betula papyrifera) appeared to decrease less than pin cherr y (Prunus pensylvanica) in years 1-2 suggesting that species compositi on on sites may influence the magnitude of effects on total browse ava ilability. The proportion of deciduous browse biomass with a relativel y high DE content (1.8 kcal/g) was not affected (P = 0.37) by treatmen t at 1-2 years, but was greater (P = 0.047) on treated than untreated clearcuts at 7-11 years posttreatment. Biomass and percent of availabl e deciduous browse eaten by moose were not affected (P > 0.1) by glyph osate in years 1-2, but were 4-5 times greater (P ( 0.1) on treated th an untreated clearcuts at 7-11 years posttreatment. The DE and protein content of moose diets on clearcuts was not affected (P > 0.1) by tre atment in either time period. Initial reductions in browse availabilit y may decrease the suitability of clearcuts for foraging by moose, but this effect would decrease over the next 5-9 years because browse ava ilability decreases naturally on untreated sites. We concluded that gl yphosate did not have important effects on diet quality. Heavy browsin g in older treated clearcuts suggests that moose may be attracted to t hese sites, but this behavior was not directly related to browse avail ability or nutrition. We discuss management options for minimizing eff ects of glyphosate treatment on moose habitat.