Incorporating habitats of plants and ungulates contributes to prioritize targets for conserving regional plant diversity

Abstract

AbstractOvergrazing caused by overabundant ungulates exceeding the land carrying capacity induces catastrophic ecological problems. Installation of ungulate‐proof fences is an effective management tool to protect plants from overgrazing. However, an efficient framework to prioritize conservation targets (i.e., plant species to be protected by the fences and areas to install the fences) for maintaining plant diversity under limited resources has yet to be formulated. At a regional scale, the possibility of plants being encountered and grazed by ungulates would increase when the habitats of plants and that of foraging ungulates overlap. We tested the utility of incorporating the encounter tendency as well as the palatability of each plant species to identify areas for preferential installation of fences to secure regional plant diversity. We conducted a plant survey in five 3 × 3 m quadrats at 30 stands at Minakami, Gunma, Japan, and recorded the presence or absence of ungulate grazing scars for all plant shoots within a height of 25–200 cm at each quadrat. We developed a regression model in which the presence or absence of a grazing scar was explained by the susceptibility of a plant species to grazing (palatability) and the susceptibility of the quadrats to visitation by ungulates (visitability). The encounter tendency of respective species was then evaluated based on the visitability of quadrats and the frequency distribution of their shoots across the quadrats. Of 211 plant species examined, 121 showed significant values of either or both palatability and encounter tendency, whereas the two metrics were mutually independent. In addition, using a simulation model, we showed that the median of the number of species lost in a region would be 1.8‐fold smaller over 20 yr when considering both the palatability and the encounter tendency to identify areas for the installation of ungulate‐proof fences as compared to considering only palatability. We suggest that accounting for both palatability and encounter tendency would greatly improve our capacity to identify priority areas for the installation of ungulate‐proof fences to efficiently ensure the persistence of regional plant diversity.