Herbivores can have large impacts on the composition and functioning of plant communities and may even drive the vegetation towards a different state. For example, grazing by reindeer can result in a shift from relatively unproductive dwarf shrub vegetation to a more nutrient rich vegetation type dominated by herbaceous plants. We studied so-called historical milking grounds (HMGs) in northern Sweden: old reindeer herding sites that were subject to high numbers of reindeer for many centuries, up to a century ago. The high reindeer concentrations in the past caused the vegetation to shift locally to small meadow-like patches, which are still clearly discernible in the otherwise heath-and shrub dominated tundra, a century after their active use.One possible mechanism for the long-term stability of HMG vegetation is the interaction with biotic and abiotic components of the soil. More specifically, a positive interaction between the vegetation and associated soil biota would help stabilize the current vegetation and slow down invasion rates of other plant species. We tested this assumption by growing seedlings representative of HMG vegetation (Potentilla crantzii) and control vegetation (Betula nana) in soils from HMGs and control sites, in a climate chamber. By sterilizing the soils, we could separate the biotic from abiotic drivers, to try and understand the different growth responses of plants in different soils. We found that,although both the typical control- and HMG plant species grew well in HMG soils due to the increased nutrient availability, microorganisms in the HMG soil provided an additional benefit for the typical HMG plant species. This was mostly the case when soils from nutrient poor habitats (heath) were considered.In summary, we conclude that positive interactions between plants, soils and soil organisms can explain the long-term stability of vegetation shifts that were caused by reindeer many centuries ago.
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Reference: Egelkraut, D., Kardol, P., De Long J.R., Olofsson, J. (2018)
The role of plant–soil feedbacks in stabilizing a reindeer‐induced vegetation shift in subarctic tundra. Functional Ecology 32:1959-1971.