Grazing by wild red deer can mitigate nutrient enrichment in protected semi-natural open habitats

Abstract

Eutrophication through atmospheric nutrient deposition is threatening the biodiversity of semi-natural habitats characterized by low nutrient availability. Accordingly, local management measures aiming at open habitat conservation need to maintain habitat-specific nutrient conditions despite atmospheric inputs. Grazing by wild herbivores, such as red deer (Cervus elaphus), has been proposed as an alternative to mechanical or livestock-based measures for preserving open habitats. The role of red deer for nutrient dynamics in protected open habitat types, however, is yet unclear. Therefore, we collected data on vegetation productivity, forage removal, quantity of red deer dung and nutrient concentrations in vegetation and dung from permanent plots in heathlands and grasslands (eight plots à 225 m2 per habitat type) on a military training area inhabited by a large population of free-ranging red deer over one year. The annual nutrient export of nitrogen (N) and phosphorus (P) by red deer grazing was higher than the nutrient import through red deer excreta, resulting in an average net nutrient removal of 14 and 30 kg N ha−1 a−1 and 1.1 and 3.3 kg P ha−1 a−1 in heathlands and grasslands, respectively. Even when considering approximate local atmospheric deposition values, net nutrient depletion due to red deer grazing seemed very likely, notably in grasslands. Demonstrating that grazing by wild red deer can mitigate the effects of atmospheric nutrient deposition in semi-natural open habitats similarly to extensive livestock grazing, our results support the idea that red deer are suitable grazing animals for open habitat conservation.

Zoogeochemistry of a protected area: Driven by anthropogenic impacts and animal behavior

“…This assertion is further corroborated by the fact that fecal nutrient concentrations in Ovstrup Hede are comparatively high in winter. Here, we found concentrations of 2.0% N and 0.4% P, which is slightly higher than those found in a PA in southern Germany (1.9% N and 0.24% P) (Riesch et al, 2022) and in natural grazing sites in Oostvaardersplassen in the Netherlands (1.6 %N and 0.3 %P) (Valdés-Correcher et al, 2019) and Montana, USA (1.5% N) (Christianson & Creel, 2007). The average fecal nitrogen concentration of deer in winter in a comparable, but fenced PA in Denmark (Klelund Dyrehave) dominated by coniferous forest and heathland, but with supplementary feeding in winter was found to be 1.7% (Fløjgaard et al, 2016).…”

How Do Nitrogen Deposition, Mowing, and Deer Grazing Drive Vegetation Changes on Dune Heaths?

“…At the study site, there is no dung removal, which contrasts with traditional heathland farming practices, where livestock dung was removed and depleted the soil of nutrients; albeit, even when livestock is not present at our study site, deer are still exporting nutrients from the dune heath [15]. However, our data show that even with deer grazing, nitrogensensitive bryophytes declined.…”

“…As a management tool, mowing and removing the material or grazing the habitat may counteract excess nitrogen on heathlands; however, data indicate that it removes less nitrogen than other conservation methods (e.g., sod-cutting) [11]. While several manipulation studies address the effects of excess nitrogen and mowing on heathland habitats e.g., [9,[11][12][13], fewer studies examine the effects of deer grazing on heathlands e.g., [14,15]. Here, we examine how nitrogen deposition, mowing, and Ecologies 2024, 5 117 deer grazing affect dune heath vegetation because, to our knowledge, no studies have investigated how all factors combined impact dune heath vegetation.…”

“…In Denmark, sheep grazed heathlands all year round, while cattle were often transported to the stables to collect their dung for fertilising fields; however, these traditional livestock farming practices have disappeared in most places [44]. In contrast, the number of deer in Denmark has been increasing in the past decades, which means that they have a significant effect on vegetation, but this may not be comparable effect to sheep and cattle due to their different feeding habits [15,45,46]. Other substantial differences exist between deer and domesticated ungulates, such as cattle and ponies; cattle and ponies have larger hooves than sheep and deer, meaning they affect the vegetation differently.…”

“…Additionally, red deer maintain the heathland ecosystem by forming open sand structures and creating early stages of succession [49]. According to [15], free-ranging red deer remove as much as 14 kg N ha −1 year −1 from heathlands and it has been concluded that it makes them suitable for heathland conservation because red deer might remove enough nitrogen to cause nutrient depletion given, of course, that nitrogen deposition levels are sufficiently low. Removing red deer with exclosures promotes a general change in species composition, reduces bare soil occurrence, and increases the height of dwarf shrubs [37,49].…”