Factors determining agricultural damage from foraging ungulates : an experimental study using exclosures in oat- and grass fields

Sammanfattning: Ungulates foraging on and damaging agricultural crops are a common phenomenon worldwide, which create conflicts between stakeholders with different economic interests. Further, the spatiotemporal distribution of food and the quality of food is often referred to as the “foodscape”. The purpose with this study was to gain knowledge about which factors determine the level of damage in crops created by foraging ungulates and investigate if drones can be used to estimate crop damage in a more efficient way. To estimate proportion biomass loss in both grass- and oat fields, I used exclosures that prevented ungulate foraging and compared the crop weight inside these exclosures with adjacent control plots that allowed foraging. Within each field, three exclosures were established, two near field edges and one in the center. Aiming to explain the variation in biomass loss, I used several different explanatory variables and conducted a linear mixed model with a backwards elimination approach, to determine the factors with the greatest impact. I also monitored all grass fields with a drone that captured multispectral images, which were used to create NDVI-maps over the fields. Further, I used the NDVI-maps and a linear mixed model to investigate if NDVI was correlated with biomass weight in grass fields. I found that proportion of arable land surrounding a field had the greatest impact on the variation in biomass loss. Proportion of arable land had a negative correlation with biomass loss for both oat- and grass fields. For grass fields, there were also a positive correlation between biomass weight in non-foraged plots and biomass loss. Furthermore, NDVI showed a strong positive correlation with biomass weight in grass fields, which suggests that drones could be used to streamline estimates of biomass loss in grass fields. In conclusion, the foodscape is an important factor determining agricultural damage by foraging ungulates. Therefore, instead of decreasing ungulate populations, more focus needs to be placed on improving the foodscape for ungulates.