Reindeer grazing reduces seed and propagule bank in the High Arctic

Abstract

It is commonly assumed that plant establishment in the High Arctic is limited by severe abiotic conditions and by a paucity of propagules and seeds. Heavy reindeer grazing may reduce plant allocation to reproduction and removes significant proportions of flowers and seeds, thus reducing contributions to seed rain and seed bank. In contrast, foraging and trampling may break up existing mature plants, increasing the vegetative propagules in the soil. To determine the effect of grazing on colonization potential in the High Arctic, two studies were carried out: (i) a comparison of seed bank inside and outside three long-term reindeer ( Rangifer tarandus platyrhnchus (Vrolic)) exclosures and (ii) an investigation of the germinable seed and propagule bank of two neighbouring peninsulas with contrasting reindeer grazing history in northwestern Svalbard (79°N, 12°E). Seed banks inside reindeer exclosures germinated significantly more seedlings (596 seedlings·m–2) than those outside (263 seedlings·m–2). Species composition and total plant cover was similar on both peninsulas, but forage-plant cover was lower on the heavily grazed peninsula (Brøggerhalvøya) than on the adjacent lightly grazed peninsula (Sarsøyra). Brøggerhalvøya had significantly lower species richness and density of seed and propagule bank (0.21 ± 0.02 germinating species per sample, 0.15 ± 0.02 propagule species per sample, 416 ± 103 seedlings·m–2, 283 ± 78 propagules·m–2) than did Sarsøyra (0.44 ± 0.40 germinating species per sample, 0.35 ± 0.03 propagule species per sample,1016 ± 188 seedlings·m–2, 782 ± 238 propagules·m–2). These results imply that reindeer depleted both the seed and the propagule banks, thus reducing the potential for colonization of disturbed areas. Grazing may, therefore, have a lasting impact on High Arctic plant communities.

Seasonal shift in factors controlling net ecosystem production in a high Arctic terrestrial ecosystem

“…Kärnefelt and Thell]. S. polaris is distributed in circumarctic regions (Myklestad 1993;Cooper 2006;Argus 2007;Kienast et al 2008) and is a common species throughout the island of Spitsbergen (Skarpe and van der Wal 2002;Ohtsuka et al 2006). It has small oval leaves approximately 1 cm in diameter, and short stems.…”

Large-scale grazing history effects on Arctic-alpine germinable seed banks

“…Furthermore, there is also evidence that high grazing pressure not only decreases the amount of flowers, but also reduces the investment on sexual reproduction in many reindeer forage species (Ehrlén 1997;Wada 1999;Bråthen and Junttila 2006). Many alpine areas are known to be already seed limited (Turnbull et al 2000;Eskelinen and Virtanen 2005) and recent studies on geese (Kuijper et al 2006) and Svalbard reindeer (Cooper 2006) have discovered intensive grazing in the High Arctic to have depleted the seed banks, thus having a lasting impact in these plant communities. Parallel with the grazing history effect, we found a regional gradient in seed density from region west and middle to region east.…”

“…Reindeer are known to pick their food nonrandomly by selecting plant reproductive parts and some species before others (White and Trudell 1980;Klein 1990;Wada 1999;Bråthen and Oksanen 2001;Cooper and Wookey 2003). As a result, reindeer can change the seed bank density (Cooper 2006) and potentially shape the composition of the plant life history traits present in the seed bank.…”

Short-term herbivory has long-term consequences in warmed and ambient high Arctic tundra

“…Grazing impacts arctic plants at the individual level through mechanisms such as compensatory growth (McIntire andHik 2002, Cooper et al 2006), and can influence arctic ecosystem functioning by reducing litter input and shifting carbon and nutrient cycles (Sjögersten et al 2012). Effects of grazing on community dynamics and diversity may also be long-lasting through a reduction in the seed bank (Kuijper et al 2006, Cooper 2006). Furthermore, studies in the Low Arctic have shown that while increasing grazing pressure can have strong immediate effects on vegetation communities, cessation of grazing does not return communities to their pre-grazing state (for example , Olofsson 2006).…”