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Effects of a Reintroduced Herbivore on Ecosystem-Level Processes:An Integrated Approach for Understanding Variable Outcomes Across Heterogeneous Landscapes

Dodge, V. J.. 2017.


Purpose of the Study: There is considerable evidence that large mammalian herbivores influence ecosystem level processes, however, their effects are often variable and hard to predict. Several frameworks have been put forward, which include other properties that might also affect ecosystem level processes, including nutrient level of dominant plants in the habitat, herbivore body size, climate type, and physical characteristics of the soil. The purpose of this study is to integrate these frameworks and incorporate gradients of herbivore activity level, soil texture and moisture to determine the effects of a large mammalian herbivore on ecosystem-level processes. Procedure: We use an 18-year-old experiment stratified across a heterogeneous landscape to examine the effects of tule elk (Cervus canadensis nannodes), a reintroduced native herbivore, on soil physical and chemical properties along the coast of northern California. Findings: Elk significantly affect soil bulk density, penetration resistance, infiltration rate, and pH, and that these effects vary among soil formations. Soil moisture and texture significantly affect nitrate and ammonium availability, and this effect can be modulated by elk. Finally, the level of elk activity can influence nutrient availability and bulk density, and the effect of elk on bulk density can in turn influence nitrate and phosphate availability Conclusions: Our study emphasizes the importance of an integrated approach to examining the effects of herbivores on ecosystem-level processes. These findings may help researchers make more accurate predictions about how large herbivores influence soil properties and processes, leading to more informed decisions with regard to conservation, restoration, reintroduction and agriculture.

Key Words

native ungulate herbivores, environmental heterogeneity, soil characteristics,nutrient cycling