Northwestern Canada is experiencing about twice the rate of climate warming compared to the rest of the Earth, resulting in the degradation of the cryosphere1. A large portion of this extensive high-latitude region is underlain by permafrost, defined as ground permanently frozen for at least two years, and covered by the forest, wetland and lake ecosystems of the boreal biome. It is still unclear how interactions between the Arctic-boreal region and the atmosphere may respond to changing climate and permafrost conditions. The eddy covariance (EC) technique2 provides the only means to quasi-continuously measure ecosystem-scale net exchanges of energy and matter and thus interactions between the land surface with the atmosphere (Fig. 1).
Figure 1: a) Eddy covariance tower at Scotty Creek (SCC) including b) a 3D-sonic anemometer and an infrared gas analyzer, c) measuring landscape- (green) and ecosystem-scale (red) net exchanges of energy and matter
Eddy covariance measurements of carbon, water and heat fluxes were the central component of the Fluxnet-Canada Research Network (FCRN). The FCRN initiative (2001-2011) provided important new insights in land surface-atmosphere interactions of Canada’s forest, wetland and grassland ecosystems. However, the FCRN initiative did not include the country’s high-latitude regions, mostly due to the lack of low-power and -maintenance instrumentation suitable for the harsh environmental conditions at remote sites and the lack of infrastructure needed to meet the requirements of the EC technique (e.g., sufficiently tall tower structures). Thus, Canada’s Arctic-boreal region remains underrepresented in FLUXNET, the global initiative integrating regional initiatives (e.g., FCRN, AmeriFlux) and in Earth system models4.
Figure 2:: The Taiga Plains ecozone and the Arctic-Boreal Vulnerability Experiment (ABoVE) study domains with four boreal forest research sites along a 2000-km latitudinal climate and permafrost gradient from permafrost-free (Old Black Spruce, OBS) over sporadic (<50%, Scotty Creek, SCC) and discontinuous (50-90%, Smith Creek, SMC), to continuous permafrost (>90%, Havikpak Creek, HPC). Trail Valley Creek (TVC) is a tundra research site just north of HPC; together these two sites characterise the forest-tundra ecotone.
The Canada Research Chair (CRC) Tier 2 in Atmospheric Biogeosciences in High Latitudes expanded the EC measurements made at the permafrost-free FCRN Old Black Spruce (OBS) site towards a 2000-km latitudinal transect (the ‘transect’) along a climate and permafrost gradient across the boreal forest of the Taiga Plains ecozone and the forest-tundra ecotone (Fig. 2). In addition to OBS, state-of-the-art EC measurements of net carbon dioxide (CO2), methane (CH4), water vapor and heat exchanges are concurrently made at Scotty Creek (SCC), Smith Creek (SMC), Havikpak Creek (HPC) and Trail Valley Creek (TVC). The transect covers the central portion of the Extended Study Domain of NASA’s Arctic-Boreal Vulnerability Experiment (ABoVE, 2015-2023) which seeks to provide “a better understanding of the vulnerability and resilience of ecosystems and society to this changing environment”5 (Fig. 2). The southern Taiga Plains ecozone is characterized by a high degree of boreal landscape fragmentation due to rapid thaw-induced forest loss. In the northern Taiga Plains ecozone, the fuzzy boreal treeline is slowly migrating into some Arctic landscapes presently occupied by dwarf-shrub and polygon tundra ecosystems which also experience tall-shrub encroachment (‘Arctic greening’). To examine the consequences of forest loss (e.g., SCC) and treeline migration across the forest-tundra ecotone (HPC), the instrumental set-up involves ‘nested’ EC systems (Fig. 1c) and a nearby tundra EC system (TVC), respectively. The EC measurements at all sites (Fig. 2) are supported by additional measurements collected in collaboration with Drs. J. Baltzer, P. Marsh and W. Quinton/all Wilfrid Laurier University (WLU) through the Northwest Territories (NWT)-WLU Partnership Agreement (2010-2030). By examining ecosystem-scale land surface-atmosphere interactions centered on the innovative use of the EC technique and in line with ABoVE, the CRC’s first-term goal (2014-2018) had been to provide a mechanistic understanding of high-latitude ecosystem function across northwestern Canada’s Arctic-boreal region under the influence of rapidly changing climate and permafrost conditions.
The instrumental and methodological efforts along the transect had been expanded during the later phase of the CRC’s first term. The focus of the CRC’s second term (2019-2023) has been on collecting and analysing concurrent radiometric- (e.g., L-band radiometry6), leaf- (e.g., plant functional traits7), whole tree- (e.g., hydraulic traits8), and plot-scale carbon and water flux (different chamber techniques) measurements made within the EC footprints at OBS, SCC, SMC, HPC and TVC (Fig. 2). Observations made at SCC, SMC, HPC and TVC are currently integrated by Environment and Climate Change Canada in the site-level benchmarking system of CLASSIC9, the land surface component of the Canadian Earth System Model10. By substantially contributing to improved boreal forest representation in initiatives such as FLUXNET, and by enhancing the ecological realism of boreal forests in Earth system models, the CRC’s second-term goal is to better constrain boreal forest productivity estimates across the Extended ABoVE Study Domain.
The described research activities are carried out on the traditional territory of the Dehcho First Nations (SCC, SMC) and the Inuvialuit people (HPC, TVC). We recognize and respect the Dehcho First Nations and Inuvialuit people as the traditional custodians of the land and waters on which we conduct our research activities.
We gratefully acknowledge infrastructure and operational support received from the Canada Research Chairs program, Natural Sciences and Engineering Research Council, Polar Continental Shelf Program, Northern Scientific Training Program, Fonds de Recherche du Québec – Nature et technologies, Canada First Excellence Research Fund, NWT Cumulative Impact Monitoring Program, NWT Environmental Studies Research Fund and Canadian Space Agency.