title: Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest-wetland landscape.
abstract: In the sporadic permafrost zone of northwestern Canada, boreal forest carbon dioxide (CO2) fluxes will be altered directly by climate change through changing meteorological forcing and indirectly through changes in landscape functioning associated with thaw-induced collapse-scar bog ('wetland') expansion. However, their combined effect on landscape-scale net ecosystem CO2exchange (NEELAND), resulting from changing gross primary productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we quantify indirect land cover change impacts on NEELANDand direct climate change impacts on modeled temperature- and light-limited NEELANDof a boreal forest-wetland landscape. Using nested eddy covariance flux towers, we find both GPP and ER to be larger at the landscape compared to the wetland level. However, annual NEELAND(-20 g C m-2) and wetland NEE (-24 g C m-2) were similar, suggesting negligible wetland expansion effects on NEELAND. In contrast, we find non-negligible direct climate change impacts when modeling NEELANDusing projected air temperature and incoming shortwave radiation. At the end of the 21st century, modeled GPP mainly increases in spring and fall due to reduced temperature limitation, but becomes more frequently light-limited in fall. In a warmer climate, ER increases year-round in the absence of moisture stress resulting in net CO2uptake increases in the shoulder seasons and decreases during the summer. Annually, landscape net CO2uptake is projected to decline by 25 ± 14 g C m-2for a moderate and 103 ± 38 g C m-2for a high warming scenario, potentially reversing recently observed positive net CO2uptake trends across the boreal biome. Thus, even without moisture stress, net CO2uptake of boreal forest-wetland landscapes may decline, and ultimately, these landscapes may turn into net CO2sources under continued anthropogenic CO2emissions. We conclude that NEELANDchanges are more likely to be driven by direct climate change rather than by indirect land cover change impacts.
authors.affiliation: Département de géographie & Centre d'études nordiques, Université de Montréal, 520 Chemin de la Côte Sainte-Catherine, Montréal, QC, H2V 2B8, Canada.
authors.forename: Manuel
authors.identifier: 0000-0003-1996-8639
authors.initials: M
authors.lastname: Helbig
authors.affiliation: Department of Geography, University of Lethbridge, Lethbridge, AB, T1K 3M4, Canada.
authors.forename: Laura E
authors.initials: LE
authors.lastname: Chasmer
authors.affiliation: Department of Atmospheric and Oceanic Sciences, University of Wisconsin-Madison, Madison, WI, 53706, USA.
authors.forename: Ankur R
authors.initials: AR
authors.lastname: Desai
authors.affiliation: Department of Geography, Swansea University, Singleton Park, Swansea, SA28PP, UK.
authors.forename: Natascha
authors.initials: N
authors.lastname: Kljun
authors.affiliation: Cold Regions Research Centre, Wilfrid Laurier University, Waterloo, ON, N2L 3C5, Canada.
authors.forename: William L
authors.initials: WL
authors.lastname: Quinton
authors.affiliation: Département de géographie & Centre d'études nordiques, Université de Montréal, 520 Chemin de la Côte Sainte-Catherine, Montréal, QC, H2V 2B8, Canada.
authors.forename: Oliver
authors.initials: O
authors.lastname: Sonnentag
mesh_terms: D002170:Canada; D002244:Carbon; D002245:Carbon Dioxide; D057231:Climate Change; D017753:Ecosystem; D065928:Forests; D066188:Taiga; D053833:Wetlands
chemical_list: D002245:Carbon Dioxide; D002244:Carbon
keywords: boreal forest; carbon dioxide; climate change; ecosystem respiration; eddy covariance; gross primary productivity; permafrost; wetlands