Grazing and fire impacts on macrolichen communities of the Seward Peninsula, Alaska, U.S.A

We sought to assess impacts of fire and grazing by reindeer and caribou on lichen communities in northwestern Alaska. Macrolichen abundance was estimated from 45, 0.38-ha plots. Eighteen of those plots, scattered throughout the southern Seward Peninsula, represented two levels of grazing, heavy and light. We found lightly grazed areas had taller lichens and greater total lichen cover than heavily grazed sites. Minor yet statistically significant changes in community structure were also observed between heavily and lightly grazed sites. However, lichen species richness did not differ by grazing status. Overall, average lichen height appears to be the best indication of grazing intensity on the Seward Peninsula. Apart from the 18 grazing plots, 8 additional plots were established in previously burned sites to represent reference conditions with a known time since disturbance date. These plots provided a framework of vegetation recovery from severe, recent disturbance towards pre-disturbance conditions. Patterns in lichen, bryophyte and vascular plant characteristics from these fire plots in combination with our findings from the grazing plots were then used to interpret the disturbance history of new plots. These new plots comprise the remaining 19 plots (of the total 45) that were sampled within the Bering Land Bridge National Preserve (BELA). We believe the location of BELA, regardless of disturbance history, is more favorable to vascular plants and Sphagnum, and lichens grow taller in response, compared to areas on the Seward Peninsula further south. In addition, lower cover in the Preserve may be attributed to site or climatic differences rather than grazing.