Abstract. Landscapes in high northern latitudes are assumed to be highly
sensitive to future global change, but the rates and long-term trajectories
of changes are rather uncertain. In the boreal zone, fires are an important
factor in climate–vegetation interactions and biogeochemical cycles. Fire
regimes are characterized by small, frequent, low-intensity fires within
summergreen boreal forests dominated by larch, whereas evergreen boreal
forests dominated by spruce and pine burn large areas less frequently but
at higher intensities. Here, we explore the potential of the monosaccharide
anhydrides (MA) levoglucosan, mannosan and galactosan to serve as proxies
of low-intensity biomass burning in glacial-to-interglacial lake sediments
from the high northern latitudes. We use sediments from Lake El'gygytgyn
(cores PG 1351 and ICDP 5011-1), located in the far north-east of Russia,
and study glacial and interglacial samples of the last 430 kyr (marine
isotope stages 5e, 6, 7e, 8, 11c and 12) that had different climate and biome
configurations. Combined with pollen and non-pollen palynomorph records from
the same samples, we assess how far the modern relationships between fire,
climate and vegetation persisted during the past, on orbital to centennial
timescales. We find that MAs attached to particulates were well-preserved
in up to 430 kyr old sediments with higher influxes from low-intensity
biomass burning in interglacials compared to glacials. MA influxes
significantly increase when summergreen boreal forest spreads closer to the
lake, whereas they decrease when tundra-steppe environments and, especially,
Sphagnum peatlands spread. This suggests that low-temperature fires are a typical
characteristic of Siberian larch forests also on long timescales. The
results also suggest that low-intensity fires would be reduced by vegetation
shifts towards very dry environments due to reduced biomass availability, as
well as by shifts towards peatlands, which limits fuel dryness. In addition,
we observed very low MA ratios, which we interpret as high contributions of
galactosan and mannosan from biomass sources other than those currently monitored,
such as the moss–lichen mats in the understorey of the summergreen boreal
forest. Overall, sedimentary MAs can provide a powerful proxy for fire
regime reconstructions and extend our knowledge of long-term natural
fire–climate–vegetation feedbacks in the high northern latitudes.
Vegetation shifts and microbial substrate utilisation in boreal forest floors of Western Canada.
