Vegetation and underplanting response to amur honeysuckle invasion and deer herbivory in mixed hardwood forests
Herbivory from wildlife and competition from invasive plants are two major deterrents to native tree regeneration and native herbaceous cover and diversity. Individually, both white-tailed deer (Odocoileus virginianus Zimmerman) and the invasive shrub Amur honeysuckle (Lonicera maackii (Rupr.) Herder) have been found to separately and negatively affect native tree and herb diversity and abundance in the Midwest. While the effects of both white-tailed deer and Amur honeysuckle have been studied independently, less is known about possible interactive effects between the two species on vegetation communities and seedling regeneration. In this study, we examined the use of underplanted seedlings for forest restoration in areas of Indiana where both white-tailed deer and Amur honeysuckle are abundant. We evaluated development of one-year-old underplanted northern red oak (Quercus rubra L.) and American chestnut ( Castanea dentata (Marsh.) Borkh) seedlings across five sites in Indiana following Amur honeysuckle removal and deer exclusion. The planted seedlings were assessed at the beginning and end of each growing season for survival, browse, and growth. Foliar nitrogen concentration and water stress of the planted seedlings were evaluated using combustion analysis and pre-dawn moisture measurements, respectively. Changes in herbaceous vegetation and natural regeneration of native tree seedlings after Amur honeysuckle removal and deer exclusion were also examined over the course of the study. The survival of underplanted American chestnut and northern red oak seedlings was greatest in the areas in which Amur honeysuckle was removed and white-tailed deer were excluded. Plant moisture stress was greater in the honeysuckle removal areas for northern red oak and American chestnut and was greater outside the deer exclosures for American chestnut. There was no difference in the proportion of seedlings browsed in areas with or without Amur honeysuckle. There also was no difference in foliar nitrogen concentration among treatments; however relative growth in height was greater in the absence of deer for both species. Native herbaceous and tree seedling richness, evenness, and diversity were greater where honeysuckle was removed, but we found no effect of deer after two years of exclusion, except for spring herb evenness for which we found lower evenness where honeysuckle or deer was present than when both were present or absent. There was no difference in species richness, diversity, or overall abundance of native tree seedlings that naturally regenerated, however, honeysuckle and white-tailed deer individually had a positive effect on the density of Acer saccharum and Fraxinus americana , respectively, while honeysuckle had a negative effect on the density of Prunus serotina. The presence of honeysuckle and deer had a positive effect on the density of elm species (Ulmus spp.). Our results indicate that the exclusion of white-tailed deer and the control of Amur honeysuckle may be necessary for successful establishment and growth of underplanted seedlings in forest restoration efforts. Amur honeysuckle removal may also be necessary for the recovery of native herbs and tree seedlings, however, the effect of deer on the overall vegetation community may require greater than two years to manifest.
Jenkins, Purdue University.
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