Beavers cut, but do not prefer, an invasive shrub, Amur honeysuckle (Lonicera maackii)

Abstract

The North American beaver is a keystone riparian obligate which creates and maintains riparian areas by building dams. Invasive shrubs are common in riparian zones in the eastern U.S., but it is not known if beavers promote or inhibit these invasions. In southwest Ohio, we investigated beaver preference for Amur honeysuckle (Lonicera maackii), a prevalent riparian invader, compared to other woody species. At each of eight sites, we identified woody stems greater than 2.5 cm diameter on two 120 × 2 m transects parallel to the water’s edge and six, 25 m secondary transects perpendicular to these, recording diameter, distance to the water’s edge, and whether cut by beaver. The roles of plant genus, diameter, and distance to water in determining which stems were cut by beaver were determined by binomial generalized regression. Beaver preference for each genus and each site was quantified with an electivity index, which utilizes the proportion of stems cut compared to available stems. Probability of stem cutting depended on genus, diameter, and distance; stems closer to water and with smaller diameter had a higher probability of being cut. Although L. maackii comprised 41% of cut stems, it was low preference for beaver at six of eight sites. Beaver electivity for L. maackii was negatively associated with the density of small diameter stems of preferred taxa (Salix, Ligustrum, Pyrus, Carya and Acer negundo). These findings indicate that beaver do not hinder L. maackii. Another non-native shrub, Elaeagnus umbellata, had high electivities, suggesting beavers may impede its invasion.