Abstract
Impediments, such as tree logs, can prevent access to saplings for deer, and can increase perceived predation risk by blocking view and escape possibilities for deer in areas with large carnivores. Therefore, impediments can influence deer foraging decisions and the trade-off between safety and food of different quality indirectly influencing tree regeneration. The aim of our study was to test how the presence of an impediment affects deer foraging behavior and tree sapling performance of eight species that differ in preference by deer. We planted saplings without, nearby and inside impediments and followed their fate for three consecutive years in Białowieża forest, Poland. We constructed 1 m high impediments of 5 × 5 m that would still allow deer to enter the impediment and forage from the saplings planted inside. However, we never recorded deer inside the impediments. Near the impediments deer visitation rate and cumulative visitation time was reduced. As a result, browsing intensity of all tree species was lower nearby and especially inside the impediment. Deer did not select different tree species without, near or inside the impediment. Due to the overall lower browsing intensity, tree saplings increased in height near the impediment and heights increased significantly within the impediment. The palatable, but browsing intolerant, Acer platanoides benefited most from the impediment as this species was highly selected and heavily browsed without an impediment. Followed by the palatable, but more browse tolerant Tilia cordata and Pyrus pyraster. In comparison, the presence of an impediment had a smaller effect on the less preferred Alnus glutinosa, Picea abies and Pinus sylvestris which survived well without an impediment. Our study showed that impediments modified deer behavior as they visited these plots less frequently and thereby indirectly reduced the browsing impact on the preferred tree species. Therefore, the potential for successful recruitment of preferred tree species is higher near an impediment, and especially when surrounded by impediment structures. In the long-term, the presence of natural impediments like tree logs allows browsing intolerant tree species to escape browsing, ultimately leading to a more diverse forest composition.
Highlights
Dead wood is an important factor enhancing forest biodiversity in general (Paillet et al, 2009), including effects on vegetation
Herba ceous plants and tree saplings often grow on tree logs (Fukasawa and Ando, 2018; Orman et al, 2016) and tree logs can act as protective structures against ungulate browsers and facilitate tree regeneration (Heinemann and Kitzberger 2006, Smit et al, 2012, van Ginkel et al, 2013, 2018, Kuijper et al, 2013), thereby influencing forest tree species composition in the long term
The aim of our study is to investigate how impediments influence deer foraging behavior and link this to tree sapling browsing intensity and performance
Summary
Dead wood is an important factor enhancing forest biodiversity in general (Paillet et al, 2009), including effects on vegetation. The lower visitation rate and foraging time near tree logs results in a reduced browsing pressure, allowing saplings to grow taller and escape above the herbivore browsing line of 200 cm (Kuijper et al, 2013; Ripple and Beschta, 2003; Smit et al, 2012; van Ginkel et al, 2018). By increasing the foraging costs, tree logs can directly (via physical pro tection) and indirectly (via protection resulting from increased perceived risk) create ‘windows of opportunity’ for successful tree regeneration (Beschta et al, 2018; Kuijper et al, 2013; Ripple and Beschta, 2006; van Ginkel et al, 2018; Winnie, 2014). The relative importance of both mechanisms for tree recruitment is currently debated (Beschta et al, 2014; Winnie, 2014, 2012)
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