Forbs in Viking lands: the effect of disturbing dominant graminoids on recruitment in tundra grasslands

Grasslands, by definition, are dominated by graminoids. Nevertheless, forbs also make up a substantial part of vascular plant diversity in grasslands and are important resources of mammalian herbivores. However, forb recruitment is constrained by successful dominant graminoids, limiting access to safe sites for germination. Disturbances created by herbivores can reduce graminoid dominance and favor forb recruitment. Here we hypothesize that intense disturbance, such as that caused by megaherbivores, promotes safe sites for forbs in such graminoid‐dominated grasslands, whereas disturbance by today's herbivores, such as small rodents, may not be sufficiently intense. We selected a total of 80 plots with either of four successful graminoid species in tundra grasslands of the Varanger Peninsula, Norway. The graminoid species were silicon‐poor or rich, and of either mat‐ or bunch‐growth form. Plots were further selected in both rodent disturbed and undisturbed areas. We manually removed the dominant graminoid in half of the plots, mimicking megaherbivore disturbance by reducing both shading capabilities and belowground rhizome and root systems. Results show that forb recruitment was significantly enhanced one year following the manual removal of all four graminoids. This effect on forb recruitment was similar among the four graminoids even though they were associated with distinct plant communities. The rodent disturbance did not enhance forb recruitment. In plots with rodent‐disturbed graminoids, the manual removal enhanced forb recruitment only in plots with silicon‐rich graminoids. Forb recruitment was further enhanced by higher levels of initial species richness, initial forb abundance, and soil moisture. Our findings support the hypothesis that intense disturbance, simulating megaherbivore effects on dominant graminoids, significantly enhances forb recruitment.