Food Supply Early in the Plant Growing Season: Influences from Elk Abundance and Precipitation
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Large herbivores interact with plant communities via grazing and trampling, and the response of plant communities to these disturbances is influenced by available moisture. Whether herbivore disturbances and available moisture influence biomass of plant communities additively or multiplicatively, however, can vary based on the temporal and spatial scale at which these factors are observed. Examining these relationships is needed to understand the dynamics of plant and herbivore populations. Early in the plant growing season, many plants put most of their energy goes towards above ground growth, and herbivore disturbances can accelerate this growth given adequate soil moisture. The relationship between these factors can also vary spatially as conditions for plant growth differ. I measured the entire food supply for a non-migratory population of elk (Cervus elaphus) in a temperate rainforest over a 15-year period when population abundance and total precipitation varied. The food supply was a 50-hectare meadow complex that was divided into 7 sectors, 2-10 hectares in size. I compared linear mixed effect models using Aikaike Information Criterion to determine whether elk abundance and total precipitation had an additive or multiplicative influence on the herbivore food supply. The selected model included elk abundance and precipitation as additive, not multiplicative, predictors of food supply. Also, the relationship between food supply and precipitation varied across sectors. Forage biomass in some sectors showed a positive asymptotic relationship with precipitation but in other sectors showed little increase with precipitation. Even in this temperate rainforest, elk herbivory influenced meadow plant communities independently of precipitation.