Editing IPCC:AR6/WGII/Chapter-14 (section)

=== 14.5.1 Terrestrial and Freshwater Ecosystems and Communities ===

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==== 14.5.1.1 Terrestrial Ecosystems: Observed Impacts and Projected Risks ====

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Evidence continues to mount about the impacts of recent climate change on species and ecosystems ( ''very high confidence'' ) (Table 14.2; [[#Weiskopf--2020|Weiskopf et al., 2020]] ). Ranges and abundances of species continue to shift in response to warming throughout North America ( ''very high confidence'' ) (Cross-Chapter Box MOVING PLATE in Chapter 5; [[#Cavanaugh--2014|Cavanaugh et al., 2014]] ; [[#Molina-Martínez--2016|Molina-Martínez et al., 2016]] ; [[#Tape--2016|Tape et al., 2016]] ; [[#Miller--2017|Miller et al., 2017]] ; [[#Pecl--2017|Pecl et al., 2017]] ; [[#Zhang--2018a|Zhang et al., 2018a]] ). Future climate change will continue to affect species and ecosystems ( ''high confidence'' ) ( [[#IPBES--2018|IPBES, 2018]] ), with differential responses related to species characteristics and ecology ( [[#D’Orangeville--2016|D’Orangeville et al., 2016]] ; [[#Weiskopf--2019|Weiskopf et al., 2019]] ). Climate change is projected to adversely affect the range, migration and habitat of caribou, an important food and cultural resource in the Arctic (CCP6; [[#Leblond--2016|Leblond et al., 2016]] ; [[#Masood--2017|Masood et al., 2017]] ; [[#Barber--2018b|Barber et al., 2018b]] ; [[#Borish--2022|Borish, 2022]] ).

'''Table 14.2 |''' Examples of observed climate-change impacts on terrestrial and freshwater ecosystems

{| class="wikitable"
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! Impact

! References

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| Local extinctions

| [[#Pomara--2014|Pomara et al. (2014)]] ; [[#Wiens--2016|Wiens (2016)]]

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| Greening and increased productivity of North American vegetation from CO 2 fertilisation

| [[#Smith--2016b|Smith et al. (2016b)]] ; [[#Zhu--2016|Zhu et al. (2016)]] ; [[#Huang--2018|Huang et al. (2018)]]

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| Changes in phenology, including migration as well as mismatches between species and with human visitation

| [[#Mayor--2017|Mayor et al. (2017)]] ; [[#Zaifman--2017|Zaifman et al. (2017)]] ; [[#Breckheimer--2020|Breckheimer et al. (2020)]]

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| Vegetation conversions, including

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| * shifts to denser forests with smaller trees
* trees to savannas and grasslands
* woody plant encroachment into grasslands
* changes in tundra plant phenology and abundance
* expansion of boreal and subalpine forests into tundra, meadows
* reduced or lack of recovery following severe fire

| [[#McIntyre--2015|McIntyre et al. (2015)]]

Bendixsen et al. (2015)

[[#Archer--2017|Archer et al. (2017)]]

[[#Myers-Smith--2019|Myers-]] [[#Smith--2019|Smith et al. (2019)]]

Juday et al. (2015); Lubetkin et al. (2017)

[[#Coop--2020|Coop et al. (2020)]] ; [[#O’Connor--2020|O’Connor et al. (2020)]] ; see Box 14.2

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| Warmer droughts reducing plant productivity and carbon sequestration

| Mekonnen et al. (2017); [[#Gampe--2021|Gampe et al. (2021)]]

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| Slowing ecosystem function recovery of vegetation to pre-disturbance conditions following droughts

| [[#Schwalm--2017|Schwalm et al. (2017)]] ; [[#Crausbay--2020|Crausbay et al. (2020)]]

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| Warming streams and lakes, and changes in seasonal flows that have affected freshwater fish distributions and populations

| [[#O’Reilly--2015|O’Reilly et al. (2015)]] ; [[#Lynch--2016|Lynch et al. (2016)]] ; [[#Poesch--2016|Poesch et al. (2016)]] ; [[#Roberts--2017b|Roberts et al. (2017b)]] ; [[#Isaak--2018|Isaak et al. (2018)]] ; [[#Christianson--2019b|Christianson et al. (2019b)]] ; Zhong et al. (2019)

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| Upstream expansion of human-mediated invasive hybridisation and enhanced risk of extinction of native salmonid species

| [[#Muhlfeld--2014|Muhlfeld et al. (2014)]]

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| Declining wetlands in western North America important for bird migrations

| [[#Donnelly--2020|Donnelly et al. (2020)]]

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| Increases in harmful freshwater algal blooms

| See [[#14.5.3|Section 14.5.3]]

|}

Climate-induced shifts in the timing of biological events (phenology) continue to be a well-documented ecological response ( ''very high confidence'' ) (Table 14.2; [[#Vose--2017|Vose et al., 2017]] ; [[#Lipton--2018|Lipton et al., 2018]] ; [[#Vose--2018|Vose et al., 2018]] ; [[#Molnar--2021|Molnar et al., 2021]] ). Reduced snow season length may potentially lead to adverse camouflage effects on animals that change coat colour ( [[#Mills--2013|Mills et al., 2013]] ; [[#Mills--2018|Mills et al., 2018]] ). Human conflicts with bears are expected to increase in response to shifts in hibernation patterns ( [[#Johnson--2018|Johnson et al., 2018]] ) and food resources ( [[#Wilder--2017|Wilder et al., 2017]] ; [[#Wilson--2017|Wilson et al., 2017]] ).

Severe ecosystem consequences of warming and drying are well documented ( ''very high confidence'' ) (Table 14.2). Significant ecosystem changes are expected from projected climate change ( ''high confidence'' ), such as in Mexican cloud forests ( [[#Helmer--2019|Helmer et al., 2019]] ), North American rangelands ( [[#Polley--2013|Polley et al., 2013]] ; [[#Reeves--2014|Reeves et al., 2014]] ) and montane forests ( [[#Stewart--2021|Stewart et al., 2021]] ; [[#Wright--2021|Wright et al., 2021]] ). Permafrost thaw is projected to increase in Alaska and Canada ( [[#DeBeer--2016|DeBeer et al., 2016]] ; see also [[#Ranasinghe--2021|Ranasinghe et al., 2021]] ), accelerating carbon release (CCP6, see also [[#Canadell--2021|Canadell et al., 2021]] ) and affecting hydrology. Predicting which species or ecosystems are vulnerable is challenging ( [[#Stephenson--2019|Stephenson et al., 2019]] ), although palaeo-ecological data (e.g., pollen, tree rings) provide context from past events to better understand current and future transformations ( [[#Nolan--2018|Nolan et al., 2018]] ).

Climate-change impacts on natural disturbances have affected ecosystems ( ''very high confidence'' ) (Table 14.2; see Box 14.2), and these impacts will increase with future climate change ( ''medium confidence'' ). Facilitated by warm, dry conditions, ‘mega-disturbances’ and synergies between disturbances that include wildfires, insect and disease outbreaks, and drought-induced tree mortality continue to affect large areas of North America ( [[#Cohen--2016|Cohen et al., 2016]] ; [[#Young--2017a|Young et al., 2017a]] ; [[#Hicke--2020|Hicke et al., 2020]] ), overwhelming adaptive capacities of species and degrading ecosystem services ( [[#Millar--2015|Millar and Stephenson, 2015]] ; [[#Stewart--2021|Stewart et al., 2021]] ). This era of mega-disturbances is expected to become more widespread and severe in coming decades ( [[#Cook--2015|Cook et al., 2015]] ; [[#Seidl--2017|Seidl et al., 2017]] ; [[#Buotte--2019|Buotte et al., 2019]] ), with potentially significant impacts on ecosystems ( [[#Allen--2015|Allen et al., 2015]] ; [[#Crausbay--2017|Crausbay et al., 2017]] ; [[#Schwalm--2017|Schwalm et al., 2017]] ; [[#Coop--2020|Coop et al., 2020]] ; [[#Dove--2020|Dove et al., 2020]] Thompson et al. 2020, Stewart et al. 2021). Effects include widespread tree mortality ( [[#Allen--2015|Allen et al., 2015]] ; [[#Kane--2017|Kane et al., 2017]] ; [[#van%20Mantgem--2018|van Mantgem et al., 2018]] ) and accelerated ecosystem transformation ( ''medium confidence'' ) ( [[#Guiterman--2018|Guiterman et al., 2018]] ; [[#Crausbay--2020|Crausbay et al., 2020]] ; [[#Munson--2020|Munson et al., 2020]] ).

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==== 14.5.1.2 Freshwater Ecosystems: Observed Impacts and Projected Risks ====

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Climate change, either directly (warming water) or indirectly (glacier and snow inputs), has affected biogeochemical cycling and species composition in North American aquatic ecosystems ( ''very high confidence'' ) (Table 14.2; [[#Moser--2005|Moser et al., 2005]] ; [[#Saros--2010|Saros et al., 2010]] ; [[#Preston--2016|Preston et al., 2016]] ), possibly amplifying other human-caused stresses on these systems ( [[#Richter--2016|Richter et al., 2016]] ). Excess nutrients associated with high farm animal density can be transported during intense rainfall events (expected to increase with climate change) causing algal blooms, fish kills and other detrimental ecological effects ( [[#Huisman--2017|Huisman et al., 2017]] ; [[#Coffey--2019|Coffey et al., 2019]] ).

Projected climate change will cause habitat loss, alter physical and biological processes, and decrease water quality in freshwater ecosystems ( ''high confidence'' ) ( [[#Poesch--2016|Poesch et al., 2016]] ; [[#Crozier--2019|Crozier et al., 2019]] ). Projected river warming of 1°C–3°C is expected to reduce thermal habitat for important salmon and trout species in the northwest USA by 5–31% ( [[#Isaak--2018|Isaak et al., 2018]] ) and in Mexico ( [[#Meza-Matty--2021|Meza-Matty et al., 2021]] ), and for multiple fish species in Canada ( [[#Poesch--2016|Poesch et al., 2016]] ). Cold-water streams at higher elevations will warm less and therefore may become climate refugia ( [[#Isaak--2016|Isaak et al., 2016]] ). Projected warming of mountain lake ecosystems ( [[#Roberts--2017b|Roberts et al., 2017b]] ; [[#Redmond--2018|Redmond, 2018]] ) will affect ecosystem processes ( [[#Preston--2016|Preston et al., 2016]] ; [[#Redmond--2018|Redmond, 2018]] ; [[#Moser--2019|Moser et al., 2019]] ). Loss of cold-water inputs from retreating glaciers are expected to adversely affect alpine stream ecosystems ( [[#Fell--2017|Fell et al., 2017]] ; [[#Giersch--2017|Giersch et al., 2017]] ). For anadromous fish species (e.g., Chinook salmon), future warming will reduce habitat suitability from river headwaters to oceans ( [[#Crozier--2021|Crozier et al., 2021]] ).

Freshwater ecosystems across North America are increasingly at risk from extreme drought, compounded by human demands for water ( [[#14.5.3|Section 14.5.3]] ; [[#Kovach--2019|Kovach et al., 2019]] ). Implications for aquatic and riparian species can vary, but it is widely agreed that these systems are highly sensitive to fluctuations in the hydrological cycle, which can increase competition by invasive species and compromise connectivity between potential cold-water refugia ( [[#Melis--2016|Melis et al., 2016]] ; [[#Poff--2019|Poff, 2019]] ).

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==== 14.5.1.3 Adaptation in Terrestrial and Freshwater Ecosystems ====

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Adaptation efforts to assess vulnerability of species and ecosystems, predict adaptive capacity and identify conservation-oriented options have increased markedly across North America (e.g., [[#Hagerman--2018|Hagerman and Pelai, 2018]] ; [[#Keeley--2018|Keeley et al., 2018]] ; [[#Thurman--2020|Thurman et al., 2020]] ; [[#Peterson%20St-Laurent--2021|Peterson St-Laurent et al., 2021]] ; [[#Thompson--2021|Thompson et al., 2021]] ). Scenario-based planning, an approach for addressing uncertainty, continues to gain traction and is regularly applied by the US National Park Service ( [[#Star--2016|Star et al., 2016]] ). Nonetheless, barriers to implementation of specific actions often exist (e.g., inflexible policies, lack of resources and stakeholder buy-in, political will), hampering progress ( [[#Stein--2013|Stein et al., 2013]] ; [[#Shi--2021|Shi and Moser, 2021]] ). Efforts to evaluate the efficacy of implemented adaptation actions are also lacking ( [[#Prober--2019|Prober et al., 2019]] ), but some cases show progress. For example, ongoing efforts are quantifying how variable water releases from the Colorado River’s Glen Canyon Dam affect endangered fish species ( [[#Melis--2016|Melis et al., 2016]] ). Nature-based Solutions (NbS) for adaptation (see Box 14.7) are increasingly being evaluated, especially at larger scales.

Effective climate-informed ecosystem management requires a well-coordinated suite of adaptation efforts (e.g., assessment, planning, funding, implementation and evaluation) that is co-produced among stakeholders, Indigenous Peoples and across sectors ( ''high confidence'' ) ( [[#Millar--2015|Millar and Stephenson, 2015]] ; [[#Dilling--2019|Dilling et al., 2019]] ). New applications of conventional strategies can be modified to achieve conservation goals under climate change ( [[#USGCRP--2019|USGCRP, 2019]] ). For example, mechanical thinning and prescribed burning (to reduce fuel loads and benefit ecosystems) could be used in combination with planting species better suited to new conditions to build resilience in western US forests to longer and hotter drought conditions ( [[#Bradford--2017|Bradford and Bell, 2017]] ; [[#Vernon--2018|Vernon et al., 2018]] ). Protection of buffer areas, such as riparian strips in arid regions and boreal ecosystems, reduces water temperature, builds resistance to invasive species, increases suitable habitat ( [[#Johnson--2016|Johnson and Almlof, 2016]] ) and facilitates protection of freshwater systems from runoff during and after intense rain events ( [[#National%20Research%20Council--2002|National Research Council, 2002]] ).

Innovative approaches may facilitate species’ responses to climate change, particularly when vulnerability is exacerbated by habitat loss and fragmentation. Strategies include improved landscape connectivity for species dispersal ( [[#Carroll--2018|Carroll et al., 2018]] ; [[#Littlefield--2019|Littlefield et al., 2019]] ; [[#Lawler--2020|Lawler et al., 2020]] ; [[#Thomas--2020|Thomas, 2020]] ) or assisted migration (also called managed relocation) to climatically suitable locations ( [[#Schwartz--2012|Schwartz et al., 2012]] ; [[#Dobrowski--2015|Dobrowski et al., 2015]] ). Examples include translocation of salmon in the Columbia River ( [[#Holsman--2012|Holsman et al., 2012]] ), genetic rescue (i.e., assisted gene flow increases genetic diversity to address local maladaptation) ( [[#Aitken--2013|Aitken and Whitlock, 2013]] ) and locating and conserving climate refugia, such as in alpine meadows of the Sierra Nevada ( [[#Javeline--2015|Javeline et al., 2015]] ; [[#Morelli--2016|Morelli et al., 2016]] ). Maintaining diverse spawning habitats and salmon runs can increase resilience of salmonid populations to climate change ( [[#Schoen--2017|Schoen et al., 2017]] ; [[#Crozier--2021|Crozier et al., 2021]] ). Newer modelling approaches can facilitate the visualisation of future management scenarios, per a recent study of fires in the southwest USA ( [[#Loehman--2018|Loehman et al., 2018]] ), in addition to technologies in genomics for monitoring species and modifying adaptive traits ( [[#Phelps--2019|Phelps, 2019]] ).

Adaptation actions have important limitations ( [[#Dow--2013|Dow et al., 2013]] ), particularly in the context of biodiversity conservation goals. ‘Hard’ limits include species extinctions and vegetation mortality events, despite conservation action (i.e., besides significant emissions reductions to mitigate warming, few if any interventions could have prevented these losses). In contrast, ‘soft’ adaptation limits exist primarily as a function of the social–ecological value systems of local communities and government entities that are reflected as goals and objectives in their management plans for ecosystems and species across North America. Soft limits are often mutable or can be removed altogether ( [[#Dow--2013|Dow et al., 2013]] ). In contrast, human modifications of landscapes that change or irreparably damage can limit adaptation by reducing connectivity and therefore range shifts ( [[#Parks--2020|Parks and Abatzoglou, 2020]] ).

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