BROWSE REMOVAL, PLANT CONDITION, AND TWINNING RATES BEFORE AND AFTER SHORT-TERM CHANGES IN MOOSE DENSITY
Keywords:Alaska, Density Dependent, , Forage, Intraspecific Competition, Nutritional Condition
We monitored forage-based indices of intraspecific competition at changing moose (Alces alces) densities to gauge short-term, density-dependent environmental feedback and to ultimately improve management of moose for elevated sustained yield. In 4 areas of interior Alaska where moose density recently changed, we evaluated the magnitude of change among 4 browse indices: proportional offtake of current annual growth biomass (OFTK), proportion of current twigs that were browsed (PTB), mean twig diameter at point of browsing (DPB), and proportion of plants with broomed architecture. In 1 area where moose density increased 100% in 6 years following effective predation control, browse removal increased 138% for OFTK, 20% for PTB, and 16–
42% for DPB of primary browse species, with a 44% increase in brooming. We also studied 3 areas where moose density declined 31–41% following elevated antlerless harvests of 2–
4 years duration. In these areas (with intervals of 3–
12 years between browse surveys) we found declines of 30–40% in OFTK, 26–68% in PTB, and 11–
37% in DPB, but changes in plant architecture were inconsistent. The proportion of parturient cows with neonate twins did not change between browse surveys, presumably because of a substantial lag time influenced by life history of the dominant reproductive cohorts and little change in browse nutrient content and digestibility. Of the 4 browse indices studied, proportional OFTK most consistently reflected the direction and magnitude of short-term changes in moose density. Area-specific measures of habitat and animal conditions at high moose density provided an objective means for gauging the capacity of the respective ecosystems to support moose and maintain forage plants. We used these measures of winter forage and moose condition to justify implementing harvest strategies and to ultimately reduce high moose densities below levels of strong negative feedback.
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