Abstract
Thaw of ice-rich permafrost soils on sloping terrain can trigger erosional disturbance events that displace large volumes of soil and sediment, kill and damage plants, and initiate secondary succession. We examined how retrogressive thaw slumps (RTS), a common form of thermo-erosional disturbance in arctic tundra, affected the local loss and re-accumulation of carbon (C) and nitrogen (N) pools in organic and surface mineral soil horizons of 18 slumps within six spatially independent sites in arctic Alaska. RTS displaced 3 kg C and 0.2 kg N per m2 from the soil organic horizon but did not alter pools of C and N in the top 15 cm of the mineral horizon. Surface soil C pools re-accumulated rapidly (32 ± 10 g C m−2 yr−1) through the first 60 years of succession, reaching levels similar to undisturbed tundra 40–64 years after disturbance. Average N re-accumulation rates (2.2 ± 1.1 g N m−2 yr−1) were much higher than expected from atmospheric deposition and biological N fixation. Finally, plant community dominance shifted from graminoids to tall deciduous shrubs, which are likely to promote higher primary productivity, biomass accumulation, and rates of nutrient cycling.
Highlights
More than half the global soil organic carbon (C) pool resides in the soils and sediments of Arctic and Boreal regions (Schuur et al 2009, Tarnocai et al 2009, Zimov et al 2006)
We used both shrub dendrochronology and radiocarbon dating of moss macrofossils at the base of the newly-formed soil organic layer to estimate when soil erosional processes ended and plant regeneration was initiated in the slumps
The additional fact of high mineral soil exposure (>50%) further supports the idea that shrub age is a better estimate of the disturbance age at this slump
Summary
More than half the global soil organic carbon (C) pool resides in the soils and sediments of Arctic and Boreal regions (Schuur et al 2009, Tarnocai et al 2009, Zimov et al 2006) This has spurred considerable interest in understanding how the C balance of these ecosystems will respond to observed and predicted climate warming (Schuur and Abbott 2011). Thaw of ice-rich soil can destabilize the ground surface, leading to catastrophic mass wasting of soil and sediment and the formation of thermoerosional disturbance features (Kokelj et al 2009, Murton 2009, Schuur et al 2008) This process mixes plant biomass with surface and deep soils, exports surface materials to aquatic ecosystems (Kokelj et al 2005, Ping et al 2011), and exposes unweathered mineral substrates (Lantz et al 2009, Schuur et al 2008). Plant community reorganization may occur via recruitment of new individuals from seeds, spores, or the vegetative propagules of damaged plants within the disturbed site (Bartleman et al 2001, Jorgenson et al 2001, Mackay and Burn 2002, Ovenden 1986, Yang et al 2010), leading to shifts in the species and functional groups that dominate after disturbance (Lantz et al 2013)
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