Increased rainfall ameliorates the negative effect of trampling on the growth of High Arctic forage lichens

Recolonisation of trampled lichen pastures in the High Arctic is dependent on the regrowth from small fragments of lichen thalli. Intact lichens have been shown to grow most rapidly during periods of sustained moisture caused by rainfall or cloudy days. Climate change models for Arctic areas predict wetter summers, milder winters and greater stochastic variability. Therefore we hypothesised that the growth of both damaged and intact Svalbard reindeer forage lichens would be increased under the future climatic scenarios. The effects of rainfall frequency, increased precipitation, and simulated cloud cover on relative growth rate (RGR) of Cetraria delisei, C. islandica and C, nivalis, from NW Svalbard were examined under controlled conditions. Low light did not depress RGR, suggesting that shading provided by increased cloud cover would not affect the lichen growth. The ability to gain mass and the RGR was lower in cut thalli than intact thalli under most watering regimes. Frequency of watering was the most important factor influencing growth, but this also interacted synergistically with quantity. Damaged thalli watered frequently grew significantly more than intact thalli watered less frequently. These results suggest that an increase in summer precipitation as predicted by climate modelling would increase the growth rate of fragmented thalli and may help to ameliorate the damage done to the Lichen thalli by reindeer trampling and grazing.