Mound-building ants increase the proportion of Gramineae in above-ground vegetation and the soil seed bank in alpine meadows

Question: The impact of ants on the vegetation and soil seed bank of alpine meadows on the Qinghai-Tibetan Plateau is largely unknown. We questioned how the mound-building ant, Camponotus herculeanus, affects the above-ground vegetation, the soil seed bank and physico-chemical properties of the soil. Location: An alpine meadow in the northeast margin of the Qinghai-Tibetan Plateau (37°40′ N, 102°32′ E), China. Methods: We used field and greenhouse studies to determine the above-ground vegetation parameters and soil physico-chemical properties, and the soil seed bank composition under the mound (UM), the herbage circle at about 10 cm width around the outside of the mound (mound edge, ME) and the area 1 m from the center of the mound (control). Results: (a) The mound edge had higher vegetation height, greater above-ground biomass, lower vegetation coverage and lower plant richness than controls; (b) Gramineae had a higher total importance value, which was based on the height, coverage and biomass of each plant species, and composed a higher biomass proportion in the mound edge than in controls (68% vs. 38%), while most of the perennial dicotyledons were restricted to the controls; (c) dicotyledons were the main seed group in the 0–8 cm layer of soil_UM (43%), soil_ME (51%) and soil_control (60%), while Gramineae had a significantly higher seed density and percentage of total seeds in the soil_UM (16,507 ± 2,882.7 seeds/m³, 28.1%) than in the soil_control (4,200 ± 799.5 seeds/m³, 10.2%); and (d) soil in the 0–8 cm layer under the mound had lower water content and lower bulk density than soil on the mound edge and in controls. Conclusions: Mound-building activity of Camponotus herculeanus increased the proportion of Gramineae and decreased the proportion of dicotyledons at the site of the study indicating, that mound building could enhance the transformation of a grass and sedges community to mainly a grass community in the alpine meadow.