Changes in vegetation in northern Alaska under scenarios of climate change, 2003-2100: implications for climate feedbacks

“Alternatively, fire could slow regional warming through the alteration of ecosystem energy balances by changing albedo; for example, reduced tree cover exposes proportionally more snow, thus increasing reflectance (Randerson et al., 2006; Euskirchen et al., 2009).”

“The distribution of deciduous shrubs has been changing in the Arctic (McGuire et al. 2007), and these dynamics have consequences for energy exchange (Chapin et al. 2005a, Euskirchen et al. 2009).”

“2009) depend on whether increases in primary productivity can offset warming-induced increases in heterotrophic soil respiration (CO2 release; Euskirchen et al. 2009) and methanogenesis in thawing permafrost (CH4 release; McGuire et al.”

“Finally, several other processes, not modeled here, could also affect the highlatitude CO2 balance, including northerly expansion of the boreal forest (34), changes to the fire regime (10, 35), or other disturbance mechanisms.”

“Marked changes in ecosystem state can have substantial impacts on the Earth system, and are beginning to be captured by Earth-system and climate models (Euskirchen et al. 2009).”

“For example, moss comprises 40% of biomass in sedge tundra ecosystems (20).”

“One of the big questions is whether boreal biomes will change gradually, as assumed by most dynamic vegetationmodels (4, 5), ormight have tipping points where changing conditions can invoke critical transitions.”

“However, under multiple scenarios of climate change it is expected that tundra biomass will increase, mainly because of B. nana (Euskirchen et al., 2009) and combined with the observed negative relationship in natural vegetation, our experimental results suggest that increased shrub biomass may…”

“Continued warming of these ecosystems will likely be accompanied by continued increases in plant growth and soil C losses; ecosystem models suggest a near cancellation of C gains and losses (6).”

“Simulations with TEM-DVM have also shown increases in deciduous shrub abundance in northern Alaska, which lead to a decrease in summer albedo and an increase in land surface heat absorption for this region (Euskirchen et al., 2009).”

“Increased temperatures and concomitant changes in vegetation patterns are expected to dramatically alter the functioning of northern ecosystems over the next few decades (Joos et al. 2001; Euskirchen et al. 2009).”

“…et al., 1995; Chapin & Shaver, 1996; Hobbie & Chapin, 1998; Shaver & Jonasson, 1999; Wahren et al., 2005; Walker et al., 2006; Biasi et al., 2008; Euskirchen et al., 2009), plant nutrient status (Aerts et al., 2009), and plant phenology (Arft et al., 1999) may increase plant C uptake,…”

“Given the measured and anticipated changes in microclimate we expect, in the longer term, over the 20–25 year lifespan typical of a LBR installation, changes in the vegetation community composition will occur (Euskirchen et al., 2009).”

“Euskirchen et al. (2009b) have estimated that changes in summer heating due to changes in the forest stand age distributions under future fire regimes in the western Arctic would reduce energy exchange because of increases in summer albedo ( 0.9 W m 2 decade 1 across climate scenarios; Table 1).”

“Therefore, a better understanding of plant–soil–climate feedbacks, with particular reference to changing shrub cover, will improve models and predictions of the impacts of future climate on tundra ecosystem function (Chapin et al. 2009; Euskirchen et al. 2009).”

“Within Arctic vegetation types, deciduous shrub species such as dwarf birch (Betula nana) are expected to respond most to changes in temperature (Euskirchen et al 2009, Walker et al 2006).”

“nana biomass will expand in the Arctic region (Euskirchen et al. 2009) with implications on the surface energy balance and the permafrost thaw (Blok et al.”

“This represents an area containing 25% of the total carbon currently stored in Arctic soils [Euskirchen et al., 2009; Lawrence and Slater, 2008; Gruber et al., 2004].”

“More favorable climate, increased atmospheric CO2, and longer growing seasons can, in theory, trigger growth and increase N stored in plant biomass (9, 10).”

“Changes in Arctic vegetation do not necessarily represent a passive response to a climate change, rather active participation can occur through a number of feedbacks (e.g., Euskirchen et al. 2009).”

“Under warmer temperatures, open-tundra ecosystems will likely be colonized by tree and shrub species (Euskirchen et al 2009).”

“Maps depicting the current distribution of northern vegetation are also needed as input to terrestrial ecosystem models (Euskirchen et al. 2009) and permafrost models (Zhang et al. 2014).”

“Plant composition and growth is strongly controlled by microsite characteristics [Minke et al., 2009] and can be stimulated by the nutrients released by disturbance [Bowden et al., 2008; Koch et al., 2014] or soil warming [Euskirchen et al., 2009].”

“Collectively, these studies also provide new capacities for ground validation of remote sensing products such as that of Bhatt et al. (2010) and also perspectives for the parameterization and verification of predictive models (sensu Wolf et al. 2008; Euskirchen et al. 2009; Wramneby et al. 2010).”

“The largest and most rapid climate feedbacks are positive feedbacks to warming associated with earlier snowmelt in Alaska (Euskirchen et al. 2009b, 2010).”

“Ecological models project increases in graminoid and shrub functional groups (Euskirchen et al. 2009), and experiments have shown that graminoid and deciduous shrub species respond positively to warming and fertilization treatments (Chapin et al. 1995; Dormann and Woodin 2002; van Wijk et al. 2004;…”

“[4] Although estimated future changes in GPP and Reco have been simulated in models, at the moment more, especially long term, measurements are required to determine realistic responses [Piao et al., 2007; Sitch et al., 2007; Euskirchen et al., 2009 ].”

“This conclusion contrasts with several recent modelling studies, which have suggested that shrub encroachment will lead to an increase in GEP and an increase in net C uptake (Sitch et al. 2007; Euskirchen et al. 2009).”

“This question will be the focus of further development of DOS-TEM coupled with a biogeochemical dynamic vegetation model (Euskirchen et al 2009).”

“…(Sturm et al. 2001; Tape et al. 2006; Forbes et al. 2010; Myers-Smith et al. 2011a; Natali et al. 2012), leading eventually to changes in the composition and structure of the arctic tundra (Chapin et al. 2005; Euskirchen et al. 2009; Elmendorf et al. 2012a) and increased carbon sequestration.”

“(Euskirchen et al., 2009) modelled changes in vegetation under different climate evolution scenarios.”

“Dwarf birch is predicted to increase in abundance and distribution under climate warming scenarios (de Groot & Wein, 1999; Bret-Harte et al., 2001; Euskirchen et al., 2009) and could enhance a positive feedback mechanism that would further increase wildfire in tundra ecosystems (Higuera et al.”

“The length of the © 2015 John Wiley & Sons Ltd, Global Change Biology, 22, 208–219 snow season and opposing growing season is an important control on green-up, vegetation productivity, and carbon feedbacks to the climate system (Euskirchen et al., 2006, 2009).”

“…temperatures are increasing the microbially active root zone in boreal and high-altitude peatlands (Updegraff et al., 2001; Pastor et al., 2003; Euskirchen et al., 2009; Koven et al., 2015), and higher levels of atmospheric CO2 are known to increase root growth at depth in shrubs and trees…”

“In contrast, Euskirchen et al. (2009) chose to use 39 different PFTs to test predictions regarding the migration of arctic plant Global distributions of plant functional types are derived from remotely sensed land-cover data sets (DeFries et al., 1995, 2000; Jung et al., 2006).”

“The apparent shift from sedge-dominated tundra to shrub-dominated tundra that we documented in the older burn sites could also have a positive feedback on climate warming due to the combination of a decrease in albedo and an increase in evapotranspiration associated with this transition [Euskirchen et al., 2009; Bonfi…”

“While climate warming benefits vegetation growth in high altitude areas (Yi et al. 2011b), it results in decreases or no change to the net ecosystem carbon uptake (Euskirchen et al. 2009).”

“Large fluxes of dissolved materials link high-latitude catchments to coasts [Holmes et al., 2012; McGuire et al., 2009], where dissolved organic C (DOC) and N may fuel microbial respiration or stimulate productivity in the Arctic Ocean [Carmack et al., 2004; Holmes et al., 2008; Le Fouest et al.,…”

“While the warming climate has increased vegetation productivity due to an increase in the length of the growing season in some areas [Euskirchen et al., 2006, 2009], warming has also stimulated respiration in other areas [Oechel et al., 1993, 2000; Ueyama et al., 2009; Hayes et al., 2011].”

“Many other studies (Wilmking et al. 2004; Walker et al. 2006; Euskirchen et al. 2009) also emphasize the complexity of plant feedbacks to climate change, however the uncertainty is considerably high (Cox et al.”

“Recent work building on the study of Chapin et al. [2005] provides a transient analysis of how changes in vegetation and snow cover of northern Alaska are likely to influence atmospheric heating during the 21st century [Euskirchen et al., 2009].”

“Tmjja was chosen as climate parameter as it roughly represents the temperature conditions during the growing season, including late spring, generally the most important single climate factor influencing the distribution, reproduction and growth of the plants in the arctic region (Hinzman et al., 2005; Euskirchen et al…”

“Ecosystem modeling has been used across Alaska to investigate the response of vegetation to climate and fire using models such as ALFRESCO, TEM, and ecosys (Rupp et al., 2007; Euskirchen et al., 2009; Genet et al., 2013; Mekonnen et al., 2019).”

“Although several tundra vegetation models exist, these models do not take into account hydrological feedbacks, the formation of thaw ponds and vegetation–permafrost feedbacks or do not include mosses as separate plant functional type (e.g. Epstein et al., 2000; Wolf et al., 2008; Euskirchen et al., 2009).”

“…of boreal SOC horizons play a critical role in regulating soil temperature and moisture dynamics as well as permafrost dynamics and net primary productivity (NPP), all of which, in turn, affect the dynamics of SOC and its physical properties (Euskirchen et al., 2009; Yi et al., 2009b, 2010).”

“In contrast to the assumption for arctic ecosystems [12,26] a naturally earlier snowmelt and thus a longer growing season (Shallow) only resulted in an increased biomass for Stellaria in terms of average but for not for peak plant sizes.”

“2007), the Terrestrial Ecosystem Model (TEM, McGuire et al. 2000; Thompson et al. 2005; Euskirchen et al. 2009), the BIOME-BGC model (Engstrom et al.”

“Finally, there is increasing evidence of the “invasion” of boreal fauna and flora into the Arctic environs (Euskirchen et al. 2009; Martin et al. 2009; Post et al. 2009).”

“2016); further, the range and abundance of dwarf birch are 172 predicted to expand in response to warming (Euskirchen et al. 2009; Myers-Smith et al. 2011).”

“Tmjja was chosen as the climate parameter as it roughly represents the temperature conditions during the growing season, including late spring, generally the most important single climate factor influencing the distribution, reproduction and growth of the plants in the arctic region (Euskirchen et al., 2009; Hinzman e…”

“Euskirchen et al. (2009) used a terrestrial ecosystem model driven with climate fields generated from three GCMs (CSIRO2, HadCM3, and PCM) following the IPCC Special Report: Emissions Scenarios (SRES) A2 scenario to estimate the maximum decline in summer albedo, which was approximately 0.02 in…”

“There is considerable need to quantify the stocks of carbon held within plant communities and the rates at which those stocks are cycled, both for predicting and modelling Arctic ecosystem responses to climate change, and for determining ecosystem feedbacks to climate (Euskirchen et al., 2009).”

“Furthermore, a decrease in albedo resulting from a decrease in snow cover over land may result in a further change in albedo through a change in the vegetation in response to surface warming (Chapin et al. 2005; Euskirchen et al. 2009).”

“We use the environmental module of DOS-TEM to estimate the changes in the timing of snowmelt, snow return, and the duration of the snow season with methodology previously implemented in Euskirchen et al (2006, 2007, 2009a, 2009b).”

“1996), model simulations (Euskirchen et al. 2009; Stinson et al. 2011; Tian et al. 2010), and remote sensingbased estimation (Running et al.”

“in particular are likely to thrive in a warmer Arctic (Euskirchen et al., 2009; Heskel et al., 2013).”

“…on larger ecosystem, landscape and atmospheric processes through altered energy balance and gas exchange (Callaghan et al 2004, Cutler 2011, Euskirchen et al 2009, Sturm et al 2005, Swann et al 2010), so an additional hypothesis is that vegetation change or stability can, in itself, lead…”

“Significant changes in both diversity and above-ground biomass have been associated with recent warming of both high Arctic (e.g., Hudson et al. 2010) and low Arctic (e.g., Euskirchen et al. 2009) sites.”

“…(e.g. Villarreal et al 2012), experimental manipulations (Hollister et al 2005, Johnson et al 2011b), remote sensing (Bhatt et al 2010, Jia et al 2003), and modeling (Euskirchen et al 2009), it is not surprising that land cover change was documented in all of the landscapes investigated.”

“…unexpected because of the exuberance with which that species sometimes responds to tundra warming experiments (BretHarte et al., 2001) and the large shrub birch increases predicted to occur with climate change in northern Alaska by integrated ecosystem models, such as in Euskirchen et al. (2009).”

“For example, the TEM model (Euskirchen et al., 2009) was designed specifically for improved representation of high-latitude processes.”

“…some earlier modeling studies indicate that rises in NPP from warmer and longer growing seasons under higher Ca will be offset by rises in Rh from warmer soils, causing little change or small declines in NEP from current values [Euskirchen et al., 2009; Grant et al., 2003; Zhuang et al., 2006].”

“Models of forests in Alaska and central Canada have incorporated dynamic organic layer accumulation [Bona et al., 2016; Carrasco et al., 2006; Yi et al., 2010; Zhuang et al., 2002], NA boreal-specific tree types, and dynamic vegetation [Euskirchen et al., 2014; Euskirchen et al., 2009].”

“…more important future changes that will reinforce modern trends of major loss of biodiversity (Butchart et al. 2010) and projections of plant community change in the Arctic (Kaplan et al. 2003; Sitch et al. 2003; Callaghan et al. 2005; Kaplan and New 2006; Wolf et al. 2008; Euskirchen et al. 2009).”