Foxes fertilize the subarctic forest and modify vegetation through denning

Abstract

Ecosystem engineers modify habitats through processes other than trophic interactions, such as by regulating soil nutrients, and can influence resource availability and quality for other organisms. Predator-mediated elemental cycling may be especially important in determining plant diversity and growth in ecosystems where soil fertility and primary productivity are low. Red foxes (Vulpes vulpes L.), top predators in the Subarctic, could engineer local ecosystems through denning, which could create biogeochemical hotspots of nutrients due to continual input of feces, urine and prey remains. We examined soil and vegetation characteristics on red fox dens and paired control sites in woodland habitats near the Arctic treeline in Manitoba, Canada. The organic soil layer on den sites had 81% more inorganic nitrogen and 250% more extractable phosphorus than in control areas. Denning also increased soil respiration and pH in the organic layer, suggesting improved soil quality and nutrient availability for plants. By enriching nutrients and disturbing soils through digging, den sites had a higher plant species ß-diversity and a greater cover of erect woody shrubs (Salix spp.), grasses (Leymus mollis (Trinius) Pilger) and weedy ephemerals compared to control sites, resulting in a regional increase in plant species richness. Our research highlights the importance of considering impacts of predators other than through their consumption of prey, and provides insight into the role of red foxes in modifying plant diversity and productivity in the Subarctic.

A cosmic view of ‘tundra gardens’: satellite imagery provides a landscape-scale perspective of Arctic fox ecosystem engineering

“…Arctic foxes re-use dens for decades or even centuries (Macpherson 1969), and through time the combination of digging burrows and the accumulation of nutrients from fox excrement and prey remains likely alters local vegetation. As noted earlier, similar nutrient-enhancement patterns are found on other predator home sites (Kurek et al 2014;Fedriani et al 2015;Kucheravy et al 2021;Lang et al 2021), supporting the hypothesis that the predators are the cause of the enhanced vegetation. Arctic foxes, and other predators, have accordingly been classified as ecosystem engineers -organisms that benefit other species through physical modifications of their environment (Jones et al 1994) -due to the unique vegetative traits localized to their dens.…”

“…For instance, predators that perennially re-use home sites may indirectly affect local plant and soil communities by concentrating prey-derived nutrients there. Soil nutrient levels and plant growth are greater at ground-nesting eagle owl ( Bubo bubo ) nests compared to reference sites (Fedriani et al 2015), whereas the combination of bioturbation (from digging burrows) and nutrient deposition by badgers ( Meles meles ) and red foxes ( Vulpes vulpes ) benefits plants around their dens (Kurek et al 2014; Kucheravy et al 2021; Lang et al 2021). To date, few studies have looked at these patch-scale predator effects from a landscape-scale perspective (but see Bump et al 2009; Gable et al 2020).…”

Red foxes enhance long‐term tree growth near the Arctic treeline

“…In each of our models, denning was a significant predictor of ring width, with higher radial growth in white spruce on dens between 1897 and 2017 at treeline, despite similarities in tree densities, climate, and age across all sites. Our previous work found that red fox dens were dominated by tall, erect shrubs, grasses, and forbs, whereas control sites are mainly dominated by prostrate shrubs, which we attributed to the higher nutrient concentrations on dens (Lang et al, 2021). The nutrients added by red foxes likely also resulted in the higher radial growth observed in white spruce.…”

“…Red foxes ( Vulpes vulpes ) are widely distributed worldwide (Larivière & Pasitschniak‐Arts, 1996) and are considered ecosystem engineers by concentrating soil nutrients through organic waste, depositing prey remains, and disturbing soils at den sites (Godó et al, 2018; Kurek et al, 2014; Lang et al, 2021). These activities alter vegetation composition on dens compared to the surrounding habitat.…”

“…These activities alter vegetation composition on dens compared to the surrounding habitat. Previously, we examined the impacts of red fox denning at the Arctic treeline, quantifying soil nutrient concentrations, soil respiration, depth of the organic soil layer, and vegetation composition on red fox dens and paired control sites (Lang et al, 2021). Soils on dens had 81% more inorganic nitrogen, 250% more extractable phosphorus, and elevated CO 2 production.…”