Journal of the Torrey Botanical Society 144(4): 379–384, 2017. Excluding deer increases the proportion of beech saplings originating from seed versus those of root sprout origin 1 Evan Frigoletto, Patrick Wylie, Sarah C. Pasquini, and Walter P. Carson 2 Department of Biological Sciences, University of Pittsburgh, A234 Langley Hall, Pittsburgh, PA 15260 Abstract. American beech (Fagus grandifolia Ehrh.) regenerates both from seed and also clonally via root sprouts. Regenerating beech saplings often form dense and depauperate understories that cast deep shade and displace co- occurring species. The relative proportion of saplings that originate from seed versus root sprouts varies widely throughout the range of beech. Although the cause for that variation remains unclear, it may be linked to canopy or soil disturbances, the spread of beech bark disease (BBD), or overabundant deer. Here, we asked whether the long- term exclusion of deer and the absence of BBD would favor the regeneration of saplings (20–150 cm tall) of seed origin versus those of sprout origin. We addressed this question using deer exclosures (16 and 60 þ yr old) and paired controls in one forest in Pennsylvania where BBD had caused major adult mortality and another where BBD was not present. We found that excluding deer significantly decreased the relative proportion of root sprouts from approximately 60% to approximately 25% in each forest, regardless of stand age, exclosure age, soil type, and presence or absence of BBD. Our findings provide evidence that deer, acting as herbivores, seed predators, agents of physical disturbance, or all of those simultaneously, create forest understories where root sprouts predominate. Although speculative, our results may apply to large regions because deer have been overabundant throughout much of the geographic range of American beech. Key words: beech bark disease, deer, Fagus grandifolia, overbrowsing, root sprouts, root suckers American beech (Fagus grandifolia Ehrh.) is a late-successional tree species that is widespread throughout the eastern deciduous forest. Regener- ation of beech in the understory occurs both from seed and clonally from root sprouts (Peterson and Jones 1997). Beech saplings originating from seed often outnumber root sprouts, although that proportion varies widely among regions and root sprouts tends to increase under harsher climatic conditions or following canopy or soil disturbanc- es (Held 1983, Morris et al. 2004). Beech bark disease (BBD) complex has caused high adult mortality of American beech throughout  50% of its range (Evans et al. 2005, and citations therein). That mortality can contribute to a dense beech understory because beech seedlings and saplings typically survive or remain uninfected, thereby creating thickets that are composed of many individuals of beech; of which, some fraction are root sprouts (Ehrlich 1934; Houston 1975, 1994; Morin et al. 2007; Garnas et al. 2011; Cale et al. 2013). Surprisingly, the degree to which BBD stimulates root sprout production is unclear. It may be that canopy and soil disturbances (whether logging, wind, or BBD) all stimulate sprouting within the understory or root sprouts might be abundant before those disturbances. Jones and Raynal (1986) determined that BBD failed to stimulate root sprout production when the parent tree was still alive. In Michigan, Petrillo and Witter (2005) found a similar proportion of root sprouts in forest stands where BBD was present (17%) versus where it was absent (21%). To our knowledge, there are no studies that report the proportion of beech root sprouts before the arrival of BBD and then after periods of mortality caused by the pathogen. For example, although Houston (1975) reported the development of beech thickets after the death of adult beech, the proportion of beech saplings that were root sprouts versus those of seed origin was not reported. Throughout much of the eastern deciduous forest biome, overabundant deer have caused substantial declines in understory diversity and favored a small subset of species that are both highly shade tolerant and also likely browse tolerant and that includes American beech (Kobe et al. 1995, Rooney 2001, Horsley et al. 2003, Co ˆte ´ et al. 2004, Long et al. 2007, Krueger et al. 2009, Nuttle et al. 2013). Beaudet and Messier (2008) demonstrated that beech root sprouts growing in the shaded understory have 20% higher 1 We thank John Dzemyan and Alejandro Royo for assistance with data collection and other critical logistics, and Eric Griffin, Nathan Brouwer, and Alejandro Royo for helpful comments on earlier drafts of the manuscript. 2 Author for correspondence: walt@pitt.edu doi: 10.3159/TORREY-D-17-00010.1 ÓCopyright 2017 by The Torrey Botanical Society Received for publication August 31, 2016, and in revised form January 9, 2017; first published September 13, 2017. 379