Top-down and bottom-up forces explain patch utilization by two deer species and forest recruitment

Abstract

Ungulates play an important role in temperate systems. Through their feeding behaviour, they can respond to vegetation by selecting patches or modify vegetation composition by herbivory. The degree in which they interact with vegetation can either reinforce landscape heterogeneity by creating disturbance or reduce heterogeneity in case of overbrowsing. This study evaluates how bottom-up (patch quality, structure), top-down forces (hunting, distance to village, forest edge) and deer features (feeding type, abundance) mediate patch utilization in a temperate forest and assess the implications of patch utilization and light on forest recruitment. Theory predicts that animals seek to maximize their energetic gains by food intake while minimizing the costs associated to foraging, such as the energy required for avoiding predators and exploiting resources. We focused on two deer species with contrasting feeding type: a browser (C. capreolus) and a mixed feeder (C. elaphus). We paired camera traps to vegetation sub-plots in ten forest sites in the Netherlands that widely ranged in deer abundance and landscape heterogeneity. Results showed that patch utilization is simultaneously explained by bottom-up, top-down forces and by deer abundance, as predicted by the safety-in-numbers hypothesis. Yet, forces best explaining patch utilization differed between deer species. Overall, higher patch utilization came with higher browsing, lower tree diversity and a large difference in forest composition: from a mix of broadleaves and conifers towards only conifers. We conclude that these two deer species, although living in the same area and belonging to the same guild, differentially perceive, interact with and shape their surrounding landscape.

The presence of wolves leads to spatial differentiation in deer browsing pressure on forest regeneration

“…However, we must remember that the earliest stand stages in commercial forests represent only a part of the total ecosystem and deer browsing pressure may be lower at other stages of forest development. Although the threat posed by human hunters is thought to be the most important determinant of cervid responses in commercial forests during the day through the hunting season 36 , 60 – 62 , we have observed a pattern of changes in the distance from the forest edge selection by deer in the face of cursorial predators. We found that open-spaced centres of large-sized clearcuts and young forests, distant from older forest edges, seem to be the safest places for deer to reduce predation risk by wolves and to browse in northern Poland.…”

Insights from a 31‐year study demonstrate an inverse correlation between recreational activities and red deer fecundity, with bodyweight as a mediator

“…It is important to understand the fitness consequences of the fear of humans as an important stressor on other species for the management and conservation of these species (Darimont et al., 2015 ; Larson et al., 2016 ; Naidoo & Burton, 2020 ). In particular, it could enhance our understanding of the mechanisms that can result in trophic cascades (Chitwood et al., 2022 ), because large‐bodied ungulates can structure landscapes such as forests (Ramirez et al., 2018 , 2023 ), affecting forest‐related plant and animal species (Svenning et al., 2015 ). Large‐bodied ungulates may be expected to fear humans more strongly than other predators, such as wolves, thereby exhibiting strong responses to humans (see Ciuti et al., 2012 ; Crawford et al., 2022 ; Zbyryt et al., 2018 ), especially hunters (Cromsigt et al., 2013 ).…”

Woodland expansion in the presence of deer: 30 years of evidence from the Cairngorms Connect landscape restoration partnership

“…An important finding was the difference in regeneration success between tree species: Scots pine showed the greatest expansion, whilst the rarer broadleaves showed limited expansion. This may partly reflect preferential browsing of broadleaves by deer (Ramirez et al, 2023), but is likely to be also a reflection of the lack of seed sources for rarer species and the requirement of some species for more open ground conditions to germinate successfully; future work as outlined above should help to elucidate this. Several authors have highlighted the merits of a spectrum of approaches to achieve woodland expansion (e.g.…”