Overgrazing is not common with wild caribou, which continually move and are dispersed in winter, but the generally more sedentary reindeer can almost completely remove the lichen cover. Recovery in that case takes 30 to 50 years. Since lichens are weakly anchored in the soil and are brittle when dry, trampling by herds can also destroy them. Heavy grazing during the 1970s reduced them considerably on the Chukotsk Peninsula. Fires are common during occasional dry vecirs in northern forests and tundras.
Lichens are quite flammable and are some of the slowest plants to recover after a fire.
Reindeer moss is especially slow. Lacking water-conducting organs iike stems and roots, lichens absorb moisture and nutrients from the atmosphere through surface cells. Dissolved and airborne materials pass freely into their cells. This makes them especially susceptible to pollutants. In industrialized areas, severe atmospheric pollution has resulted iii the elimination of many lichen species.