Effects of observed and experimental climate change on terrestrial ecosystems in northern
Canada: results from the Canadian IPY program
Supplementary Material
1 Introduction
Arctic tundra ecosystems were the focus of research in the CiCAT project (Climate Impacts on
Canadian Arctic Tundra Ecosystems: Multi-scale and Interdisciplinary Assessments;
http://ipytundra.ca). Studies were conducted at multiple scales, from satellite data analysis to genetic
analyses of soil microbial communities and included assessments of vegetation change over the past 30
years, community-based research on changes in tundra environments including berry shrubs, and
studies of the carbon fluxes in tundra ecosystems across Arctic Canada. An ecosystem modelling study,
the first of its kind in Canada, was completed based on the carbon flux research. CiCAT was linked to
the IPY core project ITEX – the International Tundra Experiment, which is a network of tundra
ecologists and sites studying the responses of tundra systems to experimental and observed changes in
climate (Henry and Molau 1997; Elmendorf et al. 2012a; www.geog.ubc.ca/itex).
The forest-tundra ecotone was the focus of the PPS Arctic Canada project (Present processes, Past
changes, Spatio-temporal variability in the Arctic delimitation zone, Canada; http://ipy-ppsa.mun.ca/).
Studies were conducted along transects from northern boreal forest through the forest-tundra to the low
Arctic tundra in sites across Canada, and along local altitudinal gradients. The objectives of PPS Arctic
Canada included determining recent change in tree and shrub distributions, correlating change with
environmental data, investigating mechanisms, spatial patterns and the role of disturbance, and
developing models to predict future changes as treeline migrates. The project also investigated the
relationship between environmental change, resource availability and human health and well-being in
the forest-tundra ecotone. The Canadian project was the largest component of the international PPS
Arctic core project in IPY, which was coordinated in Norway (Hofgaard and Harper 2011;
http://ppsarctic.nina.no/ ).
Interactions between plants and soil microbes was the focus of a project conducted in northern
Alaska (Carbon, Microbial and Plant Community Dynamics in Low-Arctic Tundra) using the longterm ecosystem experiments at Toolik Lake. The objectives of this project were to gain a better
understanding of plant interactions with mycorrhizal fungi and other soil microbes that regulate carbon
fluxes in tundra systems. Studies included investigations of the links between below and above ground
community processes regarding carbon balance and transfer. A major effort was identifying key
microbial groups in the soil involved in carbon cycling in Arctic tundra and determining how these
processes will respond to climate change.
While these three terrestrial projects are the focus of this summary and synthesis, other projects
also involved studies of northern terrestrial ecosystems. Carbon cycling and fluxes was also the focus
of a project in the northern boreal forest of the Mackenzie River region of NWT (Changing Forests and
Peatlands along the Mackenzie Valley, Northwest Territories). This project was coordinated at the
Northern Forestry Centre, Natural Resources Canada, Edmonton.
Environmental changes in the Old Crow region of northern Yukon was the focus of the project
“Yeendoo Nanh Nakhweenjit K’atr’ahanahtyaa: Environmental Change and Traditional Use in the Old
Crow Flats, Yukon” (YNNK), which was led by the Vuntut Gwitch’in First Nation in Old Crow and
involved researchers from academic and government institutions (Wolfe et al. 2011). The major
objective of the project was to use traditional knowledge and scientific studies to better understand the
changes that have been observed in the past few decades on the Old Crow Flats, a critically important
wetland system in northern Yukon (Wolfe et al. 2011).
Another project was focused on “Measuring the Impact of Climate Change on Landscape and
Water Systems in the High Arctic” and was conducted on paired watersheds on the southern coast of
Melville Island near Cape Bounty (http://geog.queensu.ca/cbawo/). While the major focus of this
project was on the hydrology and sediment fluxes in the systems (Lamoureux and Lafrenière 2009),
there were also studies linked to the CiCAT project, including experimental warming and snow fences
and measurements of CO2 fluxes over mesic tundra using a standard eddy covariance tower method
(Lafleur et al. 2012).
2 Community-based research
2.1 Observations of environmental change
The Aboriginal people in northern communities bring a wealth of experience and knowledge of their
local and regional environments, and have experienced the changes that are now commonly reported
across the circumpolar Arctic. They have seen and felt the impacts of the warming Arctic, as it has
affected their ability to use wildlife resources, to travel on the land and even to predict the weather
using traditional methods (Jolly et al. 2002). Each of the terrestrial ecosystem projects incorporated
collaborative research with community members, Aboriginal agencies and territorial governments.
Supplementary Material Fig. 1
The answers to the standardized semi-directed questionnaire were analyzed using ordination (GérinLajoie et al. 2010).
While our interviews with community members focused on changes in the environment, participants
often cited the problems of access to food resources, both from traditional practices such as hunting and
fishing, and from imported food from the south. For example, participants reported that because of
changes in the climate and the uncertainty with traditional weather forecasts, access to hunting and
fishing areas has become riskier (Jolly et al. 2002; Ford et al. 2007; Cuerrier et al. 2012). Along with
the usual variability in wildlife resources, the problems brought by changes in the climate are impacting
the availability of country food in some communities (Cuerrier et al. 2012). These impacts are a part of
food security in Arctic communities, which is an important and complex issue, beyond the scope of this
paper. Socioeconomic factors, including lack of income, employment, food prices and loss of
traditional knowledge and skills all affect access to food (Ford et al. 2007).
2.2 Community-based observations of changes in vegetation and berry production
Supplementary Materials Fig. 2
In addition, warming experiments were established in some communities over berry shrubs, using
open-top chambers (OTCs) that followed the design used in the International Tundra Experiment
(ITEX; Marion et al. 1997).
2.3 Community-based monitoring and education
Ross et al. (2012) conducted sixty interviews with IPY researchers, northern resident and integrative
science educators to evaluate researcher-led science education and outreach activities in the Yukon and
found that outreach that is culturally specific, people-focused and led by the local community’s vision
was most successful according to educators and residents. They identified factors supporting
educational outreach initiatives, and provided recommendations on how to strengthen educational
outreach partnerships. Results show that institutional barriers discourage researchers from participating
in educational outreach. Northern residents and educators viewed integrative science as an effective
method to engage students in Indigenous knowledge and standard scientific approaches, and to
encourage collaborative educational outreach partnerships amongst outreach stakeholders.
3 Vegetation
The major objective of the PPS Arctic Canada project was to measure the structure of tree populations
and vegetation along gradients from forest to tundra and along altitudinal gradients within the foresttundra. These studies were coordinated using common protocols (Hofgaard and Rees 2008;
http://ppsarctic.nina.no/). Studies of the changes in tundra vegetation in the CiCAT project were linked
to the International Tundra Experiment (ITEX) core project in IPY. ITEX is a network of scientists and
sites conducting coordinated research on the responses of tundra ecosystems to climate variability and
change. The network was established in 1990 (Henry and Molau 1997; Walker et al. 2006; Elmendorf
et al., 2012a), and developed a manual of protocols (Molau and Mølgaard 1996;
www.geog.ubc.ca/itex/manual) and a simple passive warming experiment, which is conducted at most
sites (Marion et al., 1997; Walker et al. 2006). Vegetation research at Canadian ITEX sites was one of
the cores of the CiCAT project, and allowed research during the IPY to link to previous studies at the
sites. In addition, new tundra research sites were established near communities and in National Parks.
ITEX protocols were supplemented with standardized protocols established for the CiCAT project
(www.ipytundra.ca/protocols) which allowed similar studies to be conducted at numerous sites.
3.1 Evidence for vegetation change: regional scale
Supplementary Materials Fig. 3.
3.2 Forest-tundra ecotone
Other factors facilitated seedling establishment or growth. Seedling density was found to be greater in
protected areas with potentially greater snow depth (e.g. under shrubs; next to a group of trees; Mamet
and Kershaw 2011). In the forest-tundra ecotone, snow depth is greater in areas with increased stem
density which should facilitate seedling survival leading to higher stem density and expansion of the
forest into the ecotone and seedlings into the tundra (McLeod 2001; Tape et al. 2006; Mamet and
Kershaw 2011). Greater levels of germination of spruce seeds was found near shrubs, so shrubs should
facilitate recruitment of spruce above treeline if viable seed is available (Brown et al. 2010). In
addition, the presence of a Pleurozium moss layer increased seedling growth and survival while
mineral soil had the lowest growth and survival (Wheeler et al. 2011). This is different than in the
forest where seedlings recruited on mineral soil. Disturbance may also be increasing tree recruitment
and affecting the species of regenerating trees, and disturbance of the seedbed was important for
seedling emergence in the forest and in tree islands at the Mealy Mountains (Munier et al. 2010).
Germination and seedling establishment were higher in the mineral soil disturbed by caribou activity in
lichen woodland near treeline in Quebec (Dufour Tremblay and Boudreau 2011). Although black
spruce recruitment was reduced following two short-interval fires in the Yukon, germination increased
when seed was added, suggesting seed availability is a limiting factor (Brown et al. 2010). Severe fires
burn soils deeply allowing deciduous species such as aspen and birch to establish at high densities, then
shallow organic soils are maintained by litter accumulating from productive deciduous species
(Johnstone and Chapin 2006).
Facilitation by neighbouring trees is evident in the pattern of trees within the forest-tundra ecotone
and in tree islands at some sites. Clumping of trees in the Mealy Mountains suggests that facilitation
regulates recruitment of adult trees, whereas more evenly spaced trees in the Yukon implies that
competition may be a factor affecting recruitment (De Fields 2009). However, there was little support
for regular spacing due to competition at most sites (Harper et al. 2011). In a study of several sites
across Canada, patches of trees tended to be smaller, further apart and less dense away from the forest
(Harper et al. 2011). While temperature may be a limiting factor for treeline advance, wind and snow
distribution may be a structuring factor in determining the spatial pattern of trees within the foresttundra ecotone (Harper et al. 2011). Trees in tree islands are usually short, stunted and in poor health.
Several tree islands in Churchill showed signs of expansion with seedlings establishing on the leeward
sides but there was no sign of expansion in other sites (Walker et al. 2012). However, tree islands, at
least in the Mackenzie Delta and the Mealy Mountains, are not likely to be important sources of viable
seed for infilling of the forest-tundra transition (McLeod 2001; Walker et al. 2012; Albertsen et al.
unpublished).
3.3 Arctic tundra vegetation
Supplementary Materials Fig. 4
Supplementary Materials Fig. 5
4 Soils and belowground processes
4.2 Belowground responses to experimental manipulations
Supplementary Material Fig. 6.
5 Carbon fluxes in tundra ecosystems: measurements and modelling
Prior to the IPY, research on CO2 and CH4 exchanges on Canadian Arctic tundra were very limited. In
the 1990s some research was conducted near Churchill, Manitoba on the eastern shore of Hudson Bay.
A multi-year record of CO2 exchange at a wet-sedge fen subject to seasonal drying show the wide
range in growing season NEP from a C sink of 64 g C m-2 to a source of -21 g C m-2, where the net
source occurred in a drought year (Griffis et al. 2000). Concurrent measurements at a near-by subarctic
forest showed the open forest was a large seasonal C sink compared to the fen site, varying from 1.4
times larger in a wet year to 12 times larger in dry conditions (Lafleur et al. 2001). This early research
was discontinued in 2000 and not restarted until the IPY projects began in 2007. The only other longterm site of GHG exchange measurements was established at Daring Lake, NWT in 2004. Initial
measurements of NEP on upland (mixed) tundra showed both drying and timing of snowmelt, which
had been touted as the main controls on seasonal NEP at Arctic sties, influenced interannual variation
in NEP (Lafleur and Humphreys, 2008). However, later measurements refuted the notion that snowmelt
timing was the main driver tundra NEP, instead this work suggested that summer GEP maximum was a
better predictor of seasonal NEP (Humphreys and Lafleur 2011). The only high Arctic GHG exchange
research prior to IPY took place at Alexandra Fiord, Ellesmere Island, NU. Employing static chamber
measurements at sites along a moisture gradient exposed to long-term passive warming manipulations
researchers showed that warming increased the C sink at all sites (Welker et al., 2004). The changes in
NEP were mostly driven by increased GEP, with little or no change in ER. These measurements were
repeated during the IPY and similar results were found (Edwards 2012).
5.1 Results and discussion
There was considerable variation in growing season CO2 fluxes among tundra vegetation communities
measured near the eddy covariance towers at Daring Lake (Supplementary Materials Fig. 8). Although
heath and tussock tundra tended to have smaller net fluxes than birch tundra, the component fluxes did
not always follow the same pattern. Moisture is a strong control on C fluxes at this scale. Within
similar community types (e.g., shrub or tussock) wet sites had greater fluxes than dry sites. This
relationship extends across the range of tundra communities, where volumetric soil moisture correlated
well with mean GEP and NEP among the communities. The correlation between soil moisture and ER,
although statistically significant, was not as strong (Dagg and Lafleur 2011).
Chambers have also been used to measure CH4 fluxes from different tundra types at Daring Lake
(Supplementary Materials Fig. 9a). The flux of CH4 was highly variable and dependent upon soil
wetness (Hayne, 2009). Fluxes ranged from small net uptake on the driest communities to large sources
in the wet fen hollow site where the water table was above the moss surface. Fluxes of CO2 were less
variable among tundra types and all of these sites were net CO2 sinks during the periods of
measurement. Thus, the net carbon balance (CO2 and CH4) varies greatly with some sites as C sinks
and some as sources (Supplementary Materials Fig. 9b), with the direction and strength of the balance
varying with the time integration for the global warming potential calculation.
In many regions of the Arctic, small ponds dot the tundra and can be quite numerous, in some cases
composing 10-40% of the landscape. These ponds are often associated with permafrost thawing and
therefore a likely to be a susceptible to climate change. Laurion et al. (2010) studied ponds at low and
high Arctic sites and found that all low Arctic ponds emitted CO2, whereas high Arctic ponds were
either net emitters or sinks for atmospheric CO2 depending upon chemical and biologic characteristics
of the ponds. All ponds at both sites were emitters of CH4, but rates were highly variable. As a first
approximation, assuming 5% pond cover, it was estimated that thaw ponds in the Canadian Arctic emit
96 Tg CO2 yr-1 and 1.0 Tg CH4 yr-1 (Laurion et al. 2010). These amounts are considered a conservative
estimate and are comparable with estimates from other northern regions.
Supplementary Materials Fig. 8.
Supplementary Materials Fig. 9.
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