Intra-Island Growth Variation between Balsam Fir and White Spruce Trees, Isle Royale National Park, Michigan, U.S.A

Authors: Zachary Merrill*, The University of Tennessee Knoxville Laboratory of Tree-Ring Science, Henri Grissino-Mayer, The University of Tennessee
Topics: Biogeography
Keywords: Dendrochronology, Biogeography, Moose, Trophic Cascade, Spruce-Fir
Session Type: Paper
Day: 4/12/2018
Start / End Time: 5:20 PM / 7:00 PM
Room: Grand Ballroom C, Astor, 2nd Floor
Presentation File: No File Uploaded


Isle Royale National Park in Lake Superior is well-known for advancing research in island biogeography with its research on the longest continuous predator-prey relationship studies, involving moose (Alces alces) and wolves (Canis lupus). The effect moose herbivory has on balsam fir (Abies balsamea) plays a major role in the life history of moose, especially the winter diet in which balsam fir becomes one of the only available browse species. Selective browsing by moose of preferred nitrogen-rich species has influenced the successional trajectory of the forest and changed forest composition and stand dynamics over time. Our research concerns the trees on which this trophic relationship depends. For example, what is the effect of moose herbivory on balsam fir tree growth, as well as the overall vigor of balsam fir-dominated forests? Can the growth of fir and associated white spruce (Picea glauca) be analyzed using dendrochronological methods to determine the effects of moose on growth patterns of tree species? We used tree-ring widths as a proxy to determine if growth rate suppression of balsam fir was evident and to what degree. We randomly located 20 belt transects each 100-m in length to collect core and cross-section samples from both species of various sizes and ages. Early evidence suggests moose-induced suppression in the tree-ring record, especially in the early 1990s when the moose population exploded to over 2,500 individuals. A period of release after this widespread growth suppression coincides with the die-off of 80 % of the moose population in 1997.

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