The role of plant–soil feedbacks in stabilizing a reindeer‐induced vegetation shift in subarctic tundra

Abstract

Herbivory can drive vegetation into different states of productivity and community composition, and these changes may be stable over time due to historical contingency effects. Interactions with abiotic and biotic soil components can contribute to such long‐term legacies in plant communities through stabilizing positive feedbacks. We studied the role of plant–soil feedbacks in maintaining vegetation changes caused by historical (~1350–1900 AD) reindeer herding in northern Sweden. These historical milking grounds (HMGs) consist of meadow plant communities formed in naturally nutrient‐poor heath or naturally nutrient‐rich shrub‐dominated vegetation and are still clearly visible in the landscape, a century after active use ceased. We selected two phytometer species: the forb Potentilla crantzii as representative of HMG vegetation, and the dwarf shrub Betula nana, as representative of control vegetation. We grew both species under glasshouse conditions on soils derived from replicated HMG and paired control plots, using live soils and sterilized (γ‐radiation)‐inoculated soils, to separate between biotic and abiotic soil effects. A net negative plant–soil feedback for B. nana biomass in its home (i.e., control) soil and a net positive feedback for P. crantzii in its home (i.e., HMG) soil in heath habitat was partly driven by the soil biotic community. However, abiotic differences in mineral nitrogen (N) concentrations between control and HMG soils were a stronger driver of differences in plant growth. Positive feedbacks maintaining a high mineral nutrient availability are thus important, especially in nutrient‐poor habitats. The positive plant responses to higher soil mineral N concentrations, combined with positive biotic plant–soil feedbacks, might shift the competitive balance in favour of typical HMG plant species, thereby contributing to stability of HMG plant communities. Our data indicate that herbivore‐driven changes in the interactions between plants and both biotic and abiotic components of the soil persist over long temporal scales. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.13113/suppinfo is available for this article.

Single introductions of soil biota and plants generate long‐term legacies in soil and plant community assembly

“…) and reindeer milking ground (Egelkraut et al . ) systems. Those legacies act over a much longer time scale than the twenty‐year legacy we report here.…”

“…This is a result of self‐reinforcing feedbacks between plant and soil communities and selective feeding by herbivores (Egelkraut et al . ). Together these examples from real ecosystems show that human‐induced legacies in community assembly are widespread and can affect ecosystems over very long timescales (decades‐centuries) through altered plant–soil community interactions.…”

Contrasting vegetation states do not diverge in soil organic matter storage: evidence from historical sites in tundra

“…Whereas the vegetation transition initially was culture‐driven, a multitude of mechanisms such as increased soil nutrient availability, high rodent herbivory on shrubs invading the HMGs, and interspecific plant competition partially aided by positive plant–soil feedbacks, jointly explains why these sites are so stable through time (Egelkraut et al. , ). At present, reindeer grazing pressure does not appear to differ between surrounding tundra and the HMGs (Egelkraut et al.…”

Why are plant–soil feedbacks so unpredictable, and what to do about it?

“…Drivers that operate at larger spatial scales have the potential to change the components of PSF at the ecosystem level, but how these drivers interact with other drivers across scales might vary. For example, vertebrate herbivores will likely influence PSFs at larger spatial scales (Egelkraut, Kardol, De Long, & Olofsson, ) than aboveground insect consumers (Heinze & Joshi, ) when considered individually, but competition between vertebrate and invertebrate herbivores might interact to influence PSFs (Branson & Haferkamp, ). Plant–plant interactions, such as competition and facilitation, should also be taken into account (Box ).…”