Simple quantitative method for estimation of herbage damage caused by sika deer (Cervus nippon)

Abstract

AbstractQuantitatively estimating herbage damage caused by wild herbivores, such as deer, provides a basis for developing countermeasures designed to prevent the damage. However, a simple and easy way to quantify deer damage has not yet been developed. In this study, we estimated herbage damage caused by sika deer (Cervus nippon) in three meadows of a dairy farm in central Japan during three cutting periods. We then compared the validity of quantitative estimation of herbage damage using three simple methods: by comparing plant height or plant length outside and inside a deer exclosure cage, and by estimating the density of sika deer populations using spotlight census surveys in the meadows. We also examined the effect of the timing of herbage damage (i.e. early, middle and late season) caused by sika deer on a total herbage yield during each cutting period. The decreased plant height outside of a deer exclosure had a significant and unbiased linear relationship with herbage damage caused by sika deer. However, the decreased plant length outside of a deer exclosure had a significant but biased linear relationship with herbage damage caused by sika deer. The required sample size for assessing the difference in plant height outside of a deer exclosure increased when the herbage damage was small. On the other hand, the mean density of sika deer did not have a linear relationship with herbage damage. The timing of herbage damage caused by sika deer did not significantly affect total herbage yield. These results show comparing plant height outside and within a deer exclosure provides a simple and inexpensive quantitative method that can be used to estimate herbage damage caused by sika deer. This simple method, however, can be reliable when the herbage damage is relatively large (e.g. >30%).