Experimental evidence for large carnivore risk cues reducing deer browsing intensity in a temperate forest

Intensive ungulate browsing represents a major challenge for managing
temperate forests, and only a clear understanding of the underlying
ecological processes can help to mitigate its impact. Predator-prey
interactions play a crucial role in shaping browsing patterns; however,
the lack of a comprehensive understanding of these dynamics hinders the
development of functional policies. Using an experimental approach, we
simulated large-carnivore presence using olfactory cues to examine the
effects of predation risk on deer behaviour and its consequences for
browsing intensity on tree saplings. We conducted this experiment in
eleven locations in the Bavarian Forest National Park (Germany), each
comprising four plots with olfactory cues of wolf, lynx, cow, and water
(control). In each plot, we planted 30 saplings representing the five most
common tree species in the area, which we regularly monitored to assess
browsing intensity and selectivity.  In addition, we set a camera
trap at each plot to record deer species (red and roe deer), age, sex, and
behavioural metrics like time spent vigilant, visitation duration, and
visitation frequency. This experimental design allowed comparisons of the
effects of different large carnivore on prey species while measuring
browsing intensity. Our results demonstrated that deer modified their
behaviour in response to large carnivore scent cues compared to non-risky
cues, with more pronounced effects in lynx treatments compared to
controls. Red and roe deer spent significantly less time in lynx
treatments compared to controls, especially at dawn and dusk. In spring at
dusk, we observed similar decreases in visitation duration in wolf
treatments. Notably, our findings also show increased vigilance time of
adult deer accompanied by juveniles at sites with lynx cues during winter
nights. As a consequence of these behavioural changes, we recorded a
significant reduction in browsing intensity in lynx treatments compared to
controls. However, no signs of tree species selectivity were found in
plots with large carnivores scent cues nor differences in visitation
frequency. Synthesis and applications: By analysing multiple behavioural
responses and considering relationships between different trophic guilds,
we provide unique insights into the mechanisms of predator-prey
interactions and their indirect impact on forest ecosystems. In
particular, our findings highlight the role of large carnivores in
mitigating ungulate browsing damages, which is important for managing
temperate forests (both natural and commercial) where herbivore browsing
is a significant pressure.