Effects of laboratory simulated grazing on biomass of the perennial Arctic grass Dupontia fisheri from Svalbard: Evidence of overcompensation

The perennial grass Dupontia fisheri is an important forage for reindeer (Rangifer tarandus platyrhynchus) in Svalbard. In a growth chamber experiment, biomass and tillering responses to different clipping frequencies and clipping heights, simulating different reindeer grazing pressures, were measured al two nutrition levels during two growth periods. Total accumulated biomass was reduced by clipping at high frequency, low height, or both in the first growth period, but was unaffected by clipping in the second growth period. Moreover, the reducing effect of clipping on total biomass was present at low nutrition level only; i.e. plants compensated for high simulated grazing pressure when sufficient nutrients were available. Aboveground biomass was reduced 36% by high clipping frequency in the first growth period, but, due to a 61% reduction in aboveground biomass with time in unclipped plants, clipped groups appeared to have higher mean aboveground biomass than unclipped during the second growth period. This observation could be explained by increased self-shading in the unclipped control plants over time. Although the interactions between nutrition and clipping treatments indicate that regrowth of D, fisheri is resource dependent, these results also suggest that grazing by reindeer is important for the maintenance of a high net aboveground production in D. fisheri in Svalbard.