Ungulate herbivores create patterns of forage availability, plant species composition, and soil fertility as they range across large landscapes and consume large quantities of plant material. Over time, herbivore populations fluctuate, producing great potential for spatio-temporal landscape dynamics. In this study, we extend the spatial and temporal extent of a long-term investigation of the relationship of landscape patterns to moose foraging behavior at Isle Royale National Park, MI. We examined how patterns of browse availability and consumption, plant basal area, and soil fertility changed during a recent decline in the moose population. We used geostatistics to examine changes in the nature of spatial patterns in two valleys over 18 years and across short-range and long-range distance scales. Landscape patterns of available and consumed browse changed from either repeated patches or randomly distributed patches in 1988-1992 to random point distributions by 2007 after a recent record high peak followed by a rapid decline in the moose population. Patterns of available and consumed browse became decoupled during the moose population low, which is in contrast to coupled patterns during the earlier high moose population. Distributions of plant basal area and soil nitrogen availability also switched from repeated patches to randomly distributed patches in one valley and to random point distributions in the other valley. Rapid declines in moose population density may release vegetation and soil fertility from browsing pressure and in turn create random landscape patterns.
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Acknowledgments We thank John Briggs, Knut Kielland and an anonymous reviewer for their thoughtful comments which helped us improve the paper. The staff of Isle Royale National Park provided valuable logistic support. Bradley Dewey analyzed the resin bag samples and assisted with field work during the 18 years spanning this research. This research and the earlier research of Pastor et al. (1998) were funded by the National Science Foundation’s Long-term Research in Environmental Biology Program. Without the continuous support of this program, this research would not have been possible, and we thank the officers, staff and review panels of NSF for making it so.
- Landscape patterns
- Plant-animal interactions
- Population dynamics