On Isle Royale National Park, heavy moose browsing over the past 100 years has suppressed the regeneration of many tree species, gradually resulting in a shift towards more open forests and savannas. By 1996, 16% of the forests at the southwest end of Isle Royale had become savanna and another 20% were starting to break-up. The changes in understory vegetation brought about by savanna formation have received little attention, even though the future of moose and wolf populations on Isle Royale

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... e tied to these vegetation changes. This study examined the vegetation of savannas ranging in age (date since formation) from <10 years to 80 years to examine how the ground flora changes along a successional pathway from initial forest breakup, to extensive grassland, and finally to a zootic subclimax dubbed "moose-spruce savanna." Ordination techniques were used to describe plant communities and to identify environmental variables that influence vegetation development. Non-parametric multiplicative regression was used to predict how these variables influenced individual plants and structure within the communities. Plant communities had a notable shift from forest herbs to ruderal species, especially non-native plants. This succession was influenced strongly by the underlying bedrock and hydrology altering moisture regimes and plant communities. Picea glauca and Poa pratensis competed in a dynamic inhibitory relationship. The former facilitated forest plants while the latter out-competed other plants and promoted open swards. These interactions are dramatically changing the character of Isle Royale's upland plant communities and will have important trophic consequences for the island.