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

==== 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"
|-
! Impact

! References

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| Local extinctions

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

|-
| 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)]]

|-
| 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)]]

|-
| Vegetation conversions, including

|
|-
| * 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

|-
| Warmer droughts reducing plant productivity and carbon sequestration

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

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

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

|-
| 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)

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

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

|-
| Declining wetlands in western North America important for bird migrations

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

|-
| 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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