Re-assessment of the climatic controls on the carbon and water fluxes of a boreal aspen forest over 1996-2016: Changing sensitivity to long-term climatic conditions

Peng Liu; Alan G Barr; Tianshan Zha; T Andrew Black; Rachhpal S Jassal; Zoran Nesic; Warren D Helgason; Xin Jia; Yun Tian

doi:10.1111/gcb.16218

Re-assessment of the climatic controls on the carbon and water fluxes of a boreal aspen forest over 1996-2016: Changing sensitivity to long-term climatic conditions

Glob Chang Biol. 2022 Aug;28(15):4605-4619. doi: 10.1111/gcb.16218. Epub 2022 May 14.

Authors

Peng Liu^{1

2}, Alan G Barr³, Tianshan Zha^{1

2}, T Andrew Black⁴, Rachhpal S Jassal⁴, Zoran Nesic⁴, Warren D Helgason⁵, Xin Jia^{1

2}, Yun Tian^{1

2}

Affiliations

¹ School of Soil and Water Conservation, Beijing Forestry University, Beijing, China.
² Beijing Engineering Research Center of Soil and Water Conservation, Beijing Forestry University, Beijing, China.
³ Global Institute for Water Security, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.
⁴ Biometeorology and Soil Physics Group, University of British Columbia, Vancouver, British Columbia, Canada.
⁵ Chemical and Biological Engineering, University of Saskatchewan, Saskatoon, Saskatchewan, Canada.

PMID: 35474386
DOI: 10.1111/gcb.16218

Abstract

Recent evidence suggests that the relationships between climate and boreal tree growth are generally non-stationary; however, it remains uncertain whether the relationships between climate and carbon (C) fluxes of boreal forests are stationary or have changed over recent decades. In this study, we used continuous eddy-covariance and microclimate data over 21 years (1996-2016) from a 100-year-old trembling aspen stand in central Saskatchewan, Canada to assess the relationships between climate and ecosystem C and water fluxes. Over the study period, the most striking climatic event was a severe, 3-year drought (2001-2003). Gross ecosystem production (GEP) showed larger interannual variability than ecosystem respiration (R_e ) over 1996-2016, but R_e was the dominant component contributing to the interannual variation in net ecosystem production (NEP) during post-drought years. The interannual variations in evapotranspiration (ET) and C fluxes were primarily driven by temperature and secondarily by water availability. Two-factor linear models combining precipitation and temperature performed well in explaining the interannual variation in C and water fluxes (R² > .5). The temperature sensitivities of all three C fluxes (NEP, GEP and R_e ) declined over the study period (p < .05), and, as a result, the phenological controls on annual NEP weakened. The decreasing temperature sensitivity of the C fluxes may reflect changes in forest structure, related to the over-maturity of the aspen stand at 100 years of age, and exacerbated by high tree mortality following the severe 2001-2003 drought. These results may provide an early warning signal of driver shift or even an abrupt status shift of aspen forest dynamics. They may also imply a universal weakening in the relationship between temperature and GEP as forests become over-mature, associated with the structural and compositional changes that accompany forest ageing.

Keywords: Southern boreal forest; aspen forest; carbon fluxes; climate sensitivity; long-term change; water flux.

MeSH terms

Carbon*
Ecosystem
Forests
Saskatchewan
Taiga*
Trees
Water

Substances

Water
Carbon