Characteristics Of Stem-Breaking By Moose (Alces Alces, Cervidae): A Case-Study And Worldwide Review

During foraging, moose break stems of numerous saplings in order to lower shoot tips to a height they can reach. Both stem-breaking and bedding occur throughout the range of moose and these behaviors together create disturbed patches, which increase habitat heterogeneity forest-wide. Here, we explore this phenomenon in two ways: a case study in which we quantify the size of moose beds and evaluate the physical and taxonomic extent of stem breaking for more than 300 broken trees at seven sites in western Massachusetts and Connecticut, and a literature review on stem-breaking. In our case study, moose broke the stems of 17 deciduous woody species and were twice as likely to snap main stems rather than lateral stems. After breaking a stem, moose browsed shoot tips 96% of the time. Moose snapped primarily shade-intolerant or intermediately tolerant species (92%); the frequency of broken shade-intolerant trees was 2-4 times greater than the frequency of their occurrence in the stand, and the only shade-tolerant species moose broke were shrubs or understory tree species. We measured the 10 moose beds that we encountered; they ranged in size from 1.5-3.4 m(2) (mean = 2.5 m(2)). We performed a systematic review of stem breaking by moose throughout their range and found 14 publications that characterized stem-breaking by moose in Europe and North America. These studies typically focused on a few tree species of economic importance, on how stem-breaking increased forage access to the tips of broken trees, or how moose damage in general redirected or delayed succession. The one report of stem-breaking across all species found 1% of all trees were broken, while as many as 60% of individuals of preferred species were broken at sites in both North America and Europe. Stem-breaking contributes to keeping some forest stands in an earlier stage of succession, and bedding may create small patches of crushed vegetation that may enhance local plant diversity at small spatial scales. Thus, our findings and review support previous research that characterize moose as ecosystem engineers, keystone species, or both.