Historical corrals in Fennoscandia reveal divergent legacies of concentrated reindeer densities between continental and suboceanic tundra

Aims: In the subarctic tundra, the transition of dwarf shrub-dominated into graminoid-dominated ecosystems in response to heavy reindeer grazing intensity is hypothesized to represent an ecosystem transition to another state. However, little evidence exists regarding the extent to which the original vegetation shapes the stability and composition of the new state. We hypothesized that vegetation in sites where reindeer densities were high historically remains in a graminoid-dominated state and more strongly so in the suboceanic than the continental geobotanical district. We further hypothesized that plant communities between the two geobotanical districts would be more similar in heavily grazed sites than in control tundra heaths. Location: Subarctic tundra in northernmost Fennoscandia in Finland and Norway. Methods: We located six historical reindeer corral sites used in herding activities between the late 1800s and the 1950s in two geobotanical districts: three in the suboceanic section underlain by non-acidic bedrock and three in the continental section underlain by acidic bedrock. We analyzed plant community composition using point intercept method inside the corrals and in the surrounding tundra heaths that were used as controls. Results: The graminoid abundance was higher inside the corrals than in the control heaths independent of the geobotanical district. In the suboceanic tundra heaths, however, forb abundance and species richness per plot were substantially higher inside the corrals. This led to a stronger divergence in plant community composition between the geobotanical districts. Evergreen dwarf shrub abundance did not differ between the corrals and the controls in either of the geobotanical districts, but deciduous dwarf shrub abundance was low inside the corrals in the continental district. Conclusions: Our findings support earlier findings that concentrated reindeer densities exert long legacies on tundra vegetation but reveal that the plant species composition and the diversity of the graminoid-rich vegetation state depend strongly on environmental conditions, leading to a different composition of this vegetation state in different geobotanical districts.