Forest Succession and Nutritional Carrying Capacity of Elk since the 1980 Eruption of Mount St. Helens

  • Author / Creator
    Sparkes, Shantel N
  • There has been increasing concern over declines in habitat quality for elk (Cervus elaphus) on industrial timber lands west of Mount St. Helens due to canopy closure and the loss of nutritional resources related to succession of early seral stands created by the 1980 eruption. Vegetative recovery across the landscape has varied due to the range in severity of the initial disturbance and different management practices on industrial lands vs. in the Mount St. Helens National Volcanic Monument. In this thesis, I assessed the 5-year changes in the nutritional carrying capacity (NCC) for elk (elk days/ha) within a core area of the Mount St. Helens elk population since the 1980 eruption based on digestible energy of preferred forage species using the Forage Resource Evaluation System for Habitat model (FRESH). I constrained estimates of NCC by considering only areas with a minimum amount of biomass where an elk could forage profitably (150 kg/ha), species that met digestible energy requirements of a reproductive elk in late summer (2.9 kcal/g), the maximum amount that a species could contribute to the diet (40%), and the maximum amount that a species could be consumed (100%). I also limited the contribution of an area by its relative use derived from a resource selection function (NCCconstrained), which was developed from movement data of 23 GPS-collared elk monitored in 2009-2011 in this region. I tested whether the advancing forest succession of highly disturbed areas of the Monument was offsetting the broad-scale decline in elk summer range on industrial timber lands. From 1980-1995 the NCC was higher outside than inside the Monument due to low tephra and ash, active salvage logging and replanting, and rapid forest succession on industrial forest lands typical of this region. From 2000-2010 the NCC on industrial lands declined due to canopy closure and broad-scale application of operational herbicides and their associated reduction in preferred forages, whereas inside the Monument the NCC increased, showing partial support for my hypothesis. The resource selection function indicated elk selection was most strongly influence by available digestible energy, followed by distance to forage-cover edge, distance to a public road and slope. Constraining the NCC by relative use resulted in 2-49% decrease across study years with the greatest declines on industrial lands from 1980-1990 and inside the Monument from 2000-2010. We discussed trends in estimates of elk carrying capacity to trends in the elk summer distribution, body condition, probability of pregnancy, and overwinter elk mortality across a portion of the study area and found a general correspondence. Results from this study allowed us to anticipate the consequences of current forest succession trends and provide an approach to assess future trends in elk habitat quality under alterative management scenarios.

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  • Degree
    Master of Science
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    This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.