title: The influence of vegetation and soil characteristics on active-layer thickness of permafrost soils in boreal forest.
abstract: Carbon release from thawing permafrost soils could significantly exacerbate global warming as the active-layer deepens, exposing more carbon to decay. Plant community and soil properties provide a major control on this by influencing the maximum depth of thaw each summer (active-layer thickness; ALT), but a quantitative understanding of the relative importance of plant and soil characteristics, and their interactions in determine ALTs, is currently lacking. To address this, we undertook an extensive survey of multiple vegetation and edaphic characteristics and ALTs across multiple plots in four field sites within boreal forest in the discontinuous permafrost zone (NWT, Canada). Our sites included mature black spruce, burned black spruce and paper birch, allowing us to determine vegetation and edaphic drivers that emerge as the most important and broadly applicable across these key vegetation and disturbance gradients, as well as providing insight into site-specific differences. Across sites, the most important vegetation characteristics limiting thaw (shallower ALTs) were tree leaf area index (LAI), moss layer thickness and understory LAI in that order. Thicker soil organic layers also reduced ALTs, though were less influential than moss thickness. Surface moisture (0-6 cm) promoted increased ALTs, whereas deeper soil moisture (11-16 cm) acted to modify the impact of the vegetation, in particular increasing the importance of understory or tree canopy shading in reducing thaw. These direct and indirect effects of moisture indicate that future changes in precipitation and evapotranspiration may have large influences on ALTs. Our work also suggests that forest fires cause greater ALTs by simultaneously decreasing multiple ecosystem characteristics which otherwise protect permafrost. Given that vegetation and edaphic characteristics have such clear and large influences on ALTs, our data provide a key benchmark against which to evaluate process models used to predict future impacts of climate warming on permafrost degradation and subsequent feedback to climate.
authors: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors: James P
authors: JP
authors: Fisher
authors: Geography, College of Life and Environmental Science, University of Exeter, Exeter, EX4 4RJ, UK.
authors: Cristian
authors: C
authors: Estop-Aragonés
authors: School of GeoSciences, University of Edinburgh, Kings Buildings, Edinburgh, EH9 3JN, UK.
authors: Aaron
authors: A
authors: Thierry
authors: Geography, College of Life and Environmental Science, University of Exeter, Exeter, EX4 4RJ, UK.
authors: Dan J
authors: DJ
authors: Charman
authors: Geological Survey of Canada, Natural Resources Canada, Ottawa, ON, K1A 0E8, Canada.
authors: Stephen A
authors: SA
authors: Wolfe
authors: Geography, College of Life and Environmental Science, University of Exeter, Exeter, EX4 4RJ, UK.
authors: Iain P
authors: IP
authors: Hartley
authors: Department of Geography, University of Sussex, Brighton, BN1 9QJ, UK.
authors: Julian B
authors: JB
authors: Murton
authors: School of GeoSciences, University of Edinburgh, Kings Buildings, Edinburgh, EH9 3JN, UK.
authors: Mathew
authors: M
authors: Williams
authors: Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK.
authors: Gareth K
authors: GK
authors: Phoenix
mesh_terms: D002170:Canada; D065946:Permafrost; D012987:Soil; D066188:Taiga; D014197:Trees
chemical_list: D012987:Soil
keywords: Northwest Territories; active-layer thickness; boreal forest; discontinuous zone; permafrost; structural equation modelling