Trapped? Evidence of changes in relative plant abundance after long-term grazing exclosure across the Tundra.
Herbivores alter plant communities through the effects of selective grazing based on plant palatability. There has also been a perceived link between the relative palatability of plants and ecosystem functions. By changing the relative abundance of certain plant species, prolonged or intense grazing can affect ecosystem processes and lead to land degradation. Management interventions such as grazing exclusion can help an ecosystem recover from degraded states. However, a recent study from a degraded area in Iceland showed no significant change in plant community composition after decades of grazing cessation. This lack of response to the removal of the presumed driver of degradation could indicate the ecosystems being ‘trapped’ in a degraded state. Yet, we do not know how widespread this lack of response to long-term grazing exclusion is across the tundra biome. This thesis aims to review the current grazing literature to identify if similar situations are happening elsewhere in the tundra. I reviewed articles that experimentally excluded large and medium herbivores for ten or more years. The literature search yielded 12 articles; none of which mentioned previous degradation, making them unsuitable to assess whether the ecosystems were actually trapped in a degraded state. Moreover, the coarsest taxonomical resolution reported in the available literature was based on plant growth forms, which is too broad to characterise the plant communities in terms of their relative palatability to grazers. However, by assessing studies looking at change in relative abundance for the available growth form groups I found that most groups showed no changes after the exclosure period suggesting that gazing cessation does not necessarily impact the abundance of all growth form groups.
Náttúru- og umhverfisfræði, State-and-transition models, Land degradation, Plant growth form, Tundra, Grazing exclosure, Grazing ecology
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