The eastern moose (Alces alces americana) is one of the few remaining mega-herbivores in the eastern deciduous forest. Both extinct and modern-day mega-herbivores (such as elephants, giant sloths, and wooly mammoths) are often considered ecosystem engineers, at least partly because of their large sizes and unique behaviors. Moose may alter succession and forest regeneration via both trophic and non-trophic pathways. Moose not only preferentially browse young shoots in disturbed or early successional forests, they also create disturbances via bedding, antler-rubbing, and branch-breaking. We hypothesize that branch-breaking will be accompanied by browsing of the broken tips, linking these trophic and non-tropic effects together. We also characterize the tree species, height, and size of broken trees to illustrate how this branch-breaking behavior may structure the plant community and delay succession.
Results/Conclusions
Throughout parts of Western MA and northern Connecticut, moose broke main trunks on 18 different tree species. Moose broke stems between 1.5 and 2 meters from the ground, and main trunks were broken far more often than lateral branches. Furthermore, the mean length of the stem above the break was over 3 meters. We found that moose breakage of main tree-trunks, as well as lateral branches, was accompanied by browsing on the tips of the felled trunks 96% of the time. The height of breakage coupled with browse frequency indicates that moose break trunks to access shoot tips that are out of reach. This behavior of breaking tree-trunks may keep the forest in an earlier successional stage. Moose have been observed breaking tree-trunks throughout much of their range including Alaska, Siberia, and northern Michigan. To our knowledge (and surprise), this is the first quantitative assessment of this behavior. Our results reveal that moose likely exert strong top-down impacts on young forests directly via browsing, and indirectly, through the non-trophic pathways documented here.