Succession, herbicides, forage nutrition and elk body condition at Mount St. Helens, Washington

Abstract

Concerns have been voiced over recent reductions in forest cutting, herbicide spraying, and past heavy grazing on nutritional resources for elk (Cervus elaphus) and their body condition in the Pacific Northwest. I evaluated the effects of herbicides and herbivory on elk forage in a paired, retrospective vegetation sampling design for early seral (<13yrs) forests around Mount St. Helens (MSH), Washington. Common herbicide regimes reduced elk forage for <3 years after stand initiation and shortened the period of availability of the most nutritious forages prior to forest canopy closure. Herbicide-treated early seral stands provided higher nutritional resources for elk than mid and late-seral stands. Herbivory reduced biomass, primarily of highly palatable shrub species due to reductions in plant height rather than density. I related elk body fat derived from organs collected from hunter-harvested lactating elk in fall 2011 at MSH (n=55) to the habitat surrounding kill locations. Probability of an elk being pregnant was related to body fat. Lactating females were not thinner than non-lactating female elk, and barren non-lactating individuals had the poorest body condition. The most supported model predicting body fat of lactating elk included harvest date, elevation, and elk density.