Multi-decadal patterns of vegetation succession after tundra fire on the Yukon-Kuskokwim Delta, Alaska

Alaska’s Yukon-Kuskokwim Delta (YKD) is one of the warmest parts of the
Arctic tundra biome and tundra fires are common in its upland areas. Here we combine
field measurements, Landsat observations, and quantitative cover maps for tundra plant
functional types (PFTs) to characterize multi-decadal succession and landscape change
after fire in lichen-dominated upland tundra of the YKD, where extensive wildfires
occurred in 1971–1972, 1985, 2006–2007, and 2015. Unburned tundra was
characterized by abundant lichens and low lichen cover was consistently associated
with historical fire. While we observed some successional patterns that were consistent
with earlier work in Alaskan tussock tundra, other patterns were not. In the landscape
we studied, a large proportion of pre-fire moss cover and surface peat tended to survive
fire, which favors survival of existing vascular plants and limits opportunities for seed
recruitment. Although shrub cover was much higher in 1985 and 1971–1972 burns than
in unburned tundra, tall shrubs (>0.5 m height) were rare and the PFT maps indicate
high landscape-scale variability in the degree and persistence of shrub increase after
fire. Fire has induced persistent changes in species composition and structure of upland
tundra on the YKD, but the lichen-dominated fuels and thick surface peat appear to
have limited the potential for severe fire and accompanying edaphic changes. Soil thaw
depths were about 10 cm deeper in 2006–2007 burns than in unburned tundra, but
were similar to unburned tundra in 1985 and 1971–1972 burns. Historically, repeat fire
has been rare on the YKD, and the functional diversity of vegetation has recovered
within several decades post-fire. Our findings provide a basis for predicting and
monitoring post-fire tundra succession on the YKD and elsewhere.