FOREST DISTURBANCE TYPE DIFFERENTIALLY AFFECTS SEASONAL MOOSE FORAGE

Abstract

We examined the effects of forest disturbance on forage availability, moose (Alces alces) seasonal forage selection, and predicted in vivo digestibility in eastern Maine. Wet-mass estimated and dry-mass conversions of species consumed by three tamed moose were made throughout the year (late winter, early spring, late spring, summer, fall, early winter) in budworm (Choristoneura fumiferana) defoliated, defoliated-clearcut, defoliated-clearcut-burned, and undefoliated (control) 60- to 80-year-old spruce-fir (Picea-Abies) stands. Four Treatment replicates were on sandy (deep) and 2 on silty (shallow) soils) Three plots were established on sandy soils within both 5- and 14-year-old wildlife burns. Diet samples mixed in the proportions eaten in the field and representing the species and plant parts eaten during 564 individual feeding bouts were digested (in vitro) with cattle rumen fluid, and converted to in vivo digestibility estimates using forages of known in vivo digestibility. Forage dry mass consumption and forage group selection was related to treatment, season, and with few exceptions, availability. Dry mass consumed ranged from 152 g/hr (early winter on controls) to 1,320 g/hr (summer on the 14-year-old wildlife). Digestibility of mixed diet samples changed during the growing season, but not during the dormant (November to April) period. Digestibility ranged from 29% [early spring (pre-leaf-out) on the 14-year-old wildlife] to 47% [fall (80) on defoliated-clearcut and defoliated-clearcut-burned (combined) and late spring (post-leaf-out) on the 5-year-old wildlife]. Deciduous woody species were the forage group most commonly eaten, accounting for: 15 to 70% (depending on season) of the forage consumed in controls; 25 to 70% in budworm defoliated stands; 50 to 85% in the “recently disturbed” (clearcut, clearcut and burned, 5-year-old wildfire); and 80% or greater throughout the year in the 14-year-old wildfire plots. Moose ate significant amounts of previously unobserved or what have been considered insignificant forage groups [fallen hardwood leaves, ferns, Rubus spp., and spruce (Picea spp.)]

Natural and human-caused disturbances differ in their effects on forage production and moose use. Control and budworm de foliated plots, through time, produced limited amounts of the least digestible forage. Forage production and digestibility following cutting and controlled burns were similar, and greater than that on control on budworm defoliated plots. Although the 14-year-old wildfire produced the greatest amount of available forage, digestibility was similar to that observed on control budworm to foliated plots. Forage production, up to 6 growing-seasons post-treatment, was reduced more by wildfires than the other disturbances examined.