Date of Award

5-2015

Degree Type

Thesis

Degree Name

Master of Science

Department

Biology

Program

Biology

First Advisor/Chairperson

Alan Rebertus

Second Advisor

Donna Becker

Third Advisor

Mac Strand

Abstract

Understory herbivory combined with canopy loss alters trajectories of forest succession, and in extreme cases may produce novel landscapes dominated by the groundcover layer. I investigated the response of woody species to savannas which have emerged in Isle Royale National Park as a result of moose herbivory. I used dendrochronological methods and microsite plots to describe the spatial, temporal, and competitive responses of white spruce (Picea glauca), a non-palatable species, to the savanna environment. Most tree species had lower densities in savannas, however bird-dispersed species mountain ash (Sorbus decora) and chokecherry (Prunus virginiana) were increasing in older savannas. White spruce has increased more or less synchronously in both savanna and forest sites, with new establishment favored by sites transitioning from forest to savanna. Spruce seedling density increased with forb cover and plant species richness and decreased with plant litter depth, an effect which intensified with savanna age. Spatial patterns in savannas reflected clustering attributable to seed dispersal and microsite limitation, suggesting long-sustaining patterns of microsite heterogeneity in open savannas.

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