Herbivore grazing—or trampling? Trampling effects by a large ungulate in cold high‐latitude ecosystems

Abstract

Mammalian herbivores have important top‐down effects on ecological processes and landscapes by generating vegetation changes through grazing and trampling. For free‐ranging herbivores on large landscapes, trampling is an important ecological factor. However, whereas grazing is widely studied, low‐intensity trampling is rarely studied and quantified. The cold‐adapted northern tundra reindeer (Rangifer tarandus) is a wide‐ranging keystone herbivore in large open alpine and Arctic ecosystems. Reindeer may largely subsist on different species of slow‐growing ground lichens, particularly in winter. Lichen grows in dry, snow‐poor habitats with frost. Their varying elasticity makes them suitable for studying trampling. In replicated factorial experiments, high‐resolution 3D laser scanning was used to quantify lichen volume loss from trampling by a reindeer hoof. Losses were substantial, that is, about 0.3 dm3 per imprint in dry thick lichen, but depended on type of lichen mat and humidity. Immediate trampling volume loss was about twice as high in dry, compared to humid thin (2–3 cm), lichen mats and about three times as high in dry vs. humid thick (6–8 cm) lichen mats, There was no significant difference in volume loss between 100% and 50% wetted lichen. Regained volume with time was insignificant for dry lichen, whereas 50% humid lichen regained substantial volumes, and 100% humid lichen regained almost all lost volume, and mostly within 10–20 min. Reindeer trampling may have from near none to devastating effects on exposed lichen forage. During a normal week of foraging, daily moving 5 km across dry 6‐ to 8‐cm‐thick continuous lichen mats, one adult reindeer may trample a lichen volume corresponding to about a year's supply of lichen. However, the lichen humidity appears to be an important factor for trampling loss, in addition to the extent of reindeer movement.

Synthesizing the effects of large, wild herbivore exclusion on ecosystem function

“…The carbon cycle is an integrated system that refers to both pools (storage) and fluxes (cycling between pools) of carbon. Large herbivores directly impact carbon pools and fluxes through plant consumption, trampling plants and soil, removing woody vegetation like trees, and depositing waste products (Asner & Levick, ; Heggenes et al, ; Tanentzap & Coomes, ). Large herbivores also impact carbon storage and flux indirectly.…”

Morphological and Chemical Traits of Cladonia Respond to Multiple Environmental Factors in Acidic Dry Grasslands

“…Competition with bryophytes and vascular plants is not the only stressful factor for lichens in dry grasslands, however, we found only a few correlations between traits and disturbance factors. Trampling is regarded as the main threat to Cladonia lichens [ 68 ], but the positive correlation with richly branched podetia suggests that a moderate trampling could be a positive factor in open habitats, e.g., as a major driver of dispersal [ 16 , 36 , 69 ]. Trampling has the positive effect of producing and dispersing thallus fragments and, therefore, it could be particularly beneficial for lichens with large and fragile thalli.…”

Grazing buffers the effect of climate change on the species diversity of seedlings in an alpine meadow on the Tibetan Plateau

“…Grazing also reduced the number of leguminous seedlings with sexual reproduction (Forbis, ). The selective consumption by livestock induces strong changes in the relative abundance of plant species, thereby producing important impacts on ecosystem structure and functioning (Heggenes et al, ). As is well known, palatable graminoids and legumes have a more competitive advantage than unpalatable forbs and legumes; thus, grazing may help the seedling recruitment of unpalatable forbs and legumes by decreasing their competition with graminoid species (Gallego, Distel, Camina, & Rodríguez Iglesias, ; Niu, He, Zhang, & Lechowicz, ).…”