Above- and belowground responses to long-term herbivore exclusion

Abstract

Herbivores can play an important role in determining arctic ecosystem function with effects determined in part by herbivore identity. We examined the impact of long-term (twenty-two years) small and large mammal herbivore exclusion in two arctic plant communities in northern Alaska: dry heath (DH) and moist acidic tundra (MAT). Our aims were to examine how herbivore exclusion influences (1) plant communities and (2) soil nutrient pools and microbial processes. Though herbivore absence increased moss and decreased evergreen shrub cover in MAT, there were few other significant effects on vegetation in either community. We also observed no influence of exclusion on most soil properties. However, in DH, phosphatase activity was greater in areas where small mammals alone were present, suggesting that they are altering phosphorus (P) availability, perhaps through herbivores' influence on the plant community and subsequently on competition for P with the microbial community. We conclude that herbivore impacts in the Arctic are dependent on both the plant community and herbivore identity (size). We show the importance of understanding the roles of herbivores in the Arctic and contribute to a growing number of herbivore studies in a biome likely to experience future changes in herbivore communities and ecosystem function. ARTICLE HISTORY

Large and small herbivores have strong effects on tundra vegetation in Scandinavia and Alaska

“…To understand the herbivore effect on the plant communities better, the effect on separate plant functional groups needs to be considered. Probably the most commonly known effect of reindeer is that they reduce the abundance of ground lichens in summer and winter grazing ranges (Bernes et al., 2015 ; Gough et al., 2008 ; Olofsson et al., 2004 ; Roy et al., 2020 ). We did indeed find that large herbivores had a strong negative impact on lichen abundance in all places where ground lichens were common, but no clear effect of small herbivores.…”

Response of vegetation and carbon fluxes to brown lemming herbivory in Northern Alaska

“…While our experiment showed a potentially substantial impact of lemming herbivory on the CO2 fluxes from these tundra ecosystems, we did not address the impact of varying degrees of intensity of herbivory and population cycling of brown lemmings on carbon fluxes and photosynthetic capacity of different vegetation communities. Roy et al (2020) found that herbivore presence can alter communities of vegetation differently, as herbivores play a role in regulating a variety of plant species. These herbivores can lead to significant changes in the abundance of vegetation types, allowing for the potential of the tundra during the peak growing season to switch between a carbon source to sink in the absence of herbivory (Min et al, 2021).…”

“…Several methods for analyzing the effects of lemmings on Arctic vegetation have been documented. Most of these studies focused on ecosystem functioning in the absence of lemmings (Lara et al, 2017;Lindén et al, 2021;Min et al, 2021), the impacts of lemming waste products and carcasses on nutrient cycling and vegetation (McKendrick et al, 1980;Roy et al, 2020), the disturbance to soil via turnover by burrowing and fecal production (McKendrick et al, 1980), and recruitment and loss of forest vegetation (Ericson, 1977). This leaves a crucial gap in our understanding of how one of the main herbivores in a rapidly changing ecosystem may affect carbon cycling.…”

Herbivores in Arctic ecosystems: Effects of climate change and implications for carbon and nutrient cycling

“…Similarly, high densities of domesticated Rangifer can reverse such shrub expansion 83 . Exclusion of small mammals also increased deciduous and evergreen shrub abundance in tundra 31,80 and the forest‐tundra ecotone 84 . Herbivore‐induced reductions in shrub abundance are broadly relevant to arctic element dynamics, because they could counteract some effects of climate‐induced shrub expansion 21 .…”

“…Herbivore‐induced reductions in shrub abundance are broadly relevant to arctic element dynamics, because they could counteract some effects of climate‐induced shrub expansion 21 . However, in some cases, interactions among shrubs and vertebrate herbivores are weak 85,86 or dependent on ecosystem type 80 . Moth outbreaks in Greenland also dramatically reduce the biomass and aboveground production of deciduous shrubs, 47,48 but it remains unexplored whether low levels of background invertebrate herbivory 10,44 affect community composition more generally.…”