Satellite-detected Decreases in Caribou Lichen Cover, Cladonia (Cladina) spp., Over Eastern Canada During the Last Three Decades

Liming He
Wenjun Chen
Robert Fraser
Isabella Schmelzer
Andre Arsenault
Sylvain Leblanc
Julie Lovitt
Peter White
Sabrina Plante
Alexis Brodeur
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Caribou lichens, Cladonia (Cladina) spp., are a slow-growing, vital winter forage for caribou that are likely to be influenced by global warming. However, the large-scale response of caribou lichens to changing global climate remains unclear. Here, we derived caribou lichen cover maps for two time periods ∼30 years apart (i.e., the late 1980 s, and 2020 s) using Landsat satellite imagery for a region (0.59 million km2) in Eastern Canada that includes all or portions of several boreal caribou population ranges. We restricted our assessment to regions with at least 10% lichen cover and evaluated differences between the two time periods. Results show that since the 1980 s satellite-derived lichen cover declined in 62% of the region evaluated, remained constant in 27%, and increased in 11%. Twenty-three percent of the lichen cover decrease occurred in areas that burned after 1980, while 77% of the decrease remains unexplained, with warming-induced shrub encroachment, and caribou presence and grazing both possible causes. Caribou lichen regeneration occurs within regions burned before the 1980 s. Given that shrubification and wildfire frequency are projected to continue increasing, further monitoring of the scale and scope of ongoing changes will help to clarify future patterns. However, our results strongly suggest that the amount of caribou lichens has declined overall.