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Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest–wetland landscape

Helbig, Manuel; Chasmer, Laura; Desai, Ankur R.; Kljun, Natascha LU ; Quinton, William L. and Sonnentag, Oliver (2017) In Global Change Biology 23(8). p.3231-3248
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 CO2 exchange (NEELAND), resulting from changing gross primary productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we quantify indirect land cover change impacts on NEELAND and direct climate change impacts on modeled temperature‐ and light‐limited NEELAND of a boreal forest–wetland landscape. Using nested eddy covariance flux towers, we find both GPP and... (More)
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 CO2 exchange (NEELAND), resulting from changing gross primary productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we quantify indirect land cover change impacts on NEELAND and direct climate change impacts on modeled temperature‐ and light‐limited NEELAND of 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 NEELAND using 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 CO2 uptake increases in the shoulder seasons and decreases during the summer. Annually, landscape net CO2 uptake is projected to decline by 25 ± 14 g C m−2 for a moderate and 103 ± 38 g C m−2 for a high warming scenario, potentially reversing recently observed positive net CO2 uptake trends across the boreal biome. Thus, even without moisture stress, net CO2 uptake of boreal forest–wetland landscapes may decline, and ultimately, these landscapes may turn into net CO2 sources under continued anthropogenic CO2 emissions. We conclude that NEELAND changes are more likely to be driven by direct climate change rather than by indirect land cover change impacts. (Less)
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author
publishing date
type
Contribution to journal
publication status
published
subject
keywords
climate change, ecosystem respiration, eddy covariance, gross primary productivity, permafrost, wetlands
in
Global Change Biology
volume
23
issue
8
pages
3231 - 3248
publisher
Wiley-Blackwell
external identifiers
  • scopus:85013997063
ISSN
1354-1013
DOI
10.1111/gcb.13638
language
English
LU publication?
no
id
459a48de-e900-473d-8d86-606432ef479a
date added to LUP
2018-04-16 14:54:24
date last changed
2019-08-14 04:14:33
@article{459a48de-e900-473d-8d86-606432ef479a,
  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 CO2 exchange (NEELAND), resulting from changing gross primary productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we quantify indirect land cover change impacts on NEELAND and direct climate change impacts on modeled temperature‐ and light‐limited NEELAND of 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 NEELAND using 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 CO2 uptake increases in the shoulder seasons and decreases during the summer. Annually, landscape net CO2 uptake is projected to decline by 25 ± 14 g C m−2 for a moderate and 103 ± 38 g C m−2 for a high warming scenario, potentially reversing recently observed positive net CO2 uptake trends across the boreal biome. Thus, even without moisture stress, net CO2 uptake of boreal forest–wetland landscapes may decline, and ultimately, these landscapes may turn into net CO2 sources under continued anthropogenic CO2 emissions. We conclude that NEELAND changes are more likely to be driven by direct climate change rather than by indirect land cover change impacts. },
  author       = {Helbig, Manuel and Chasmer, Laura and Desai, Ankur R. and Kljun, Natascha and Quinton, William L. and Sonnentag, Oliver},
  issn         = {1354-1013},
  keyword      = {climate change,ecosystem respiration,eddy covariance,gross primary productivity,permafrost,wetlands},
  language     = {eng},
  month        = {01},
  number       = {8},
  pages        = {3231--3248},
  publisher    = {Wiley-Blackwell},
  series       = {Global Change Biology},
  title        = {Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest–wetland landscape},
  url          = {http://dx.doi.org/10.1111/gcb.13638},
  volume       = {23},
  year         = {2017},
}