Editing IPCC:AR6/SROCC/Chapter-2 (section)

==== 2.3.3.1 Terrestrial Biota ====

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The cryosphere can play a critical role in moderating and driving how species respond to climate change in high mountains ( ''high confidence'' ). Many mountain plant and animal species have changed abundances and migrated upslope while expanding or contracting their ranges over the past decades to century, whereas others show no change ( Morueta-Holme et al., 2015 <sup>[[#fn:r710|710]]</sup> ; Suding et al., 2015 <sup>[[#fn:r711|711]]</sup> ; Lesica and Crone, 2016 <sup>[[#fn:r712|712]]</sup> ; Fadrique et al., 2018 <sup>[[#fn:r713|713]]</sup> ; Freeman et al., 2018 <sup>[[#fn:r714|714]]</sup> ; Rumpf et al., 2018 <sup>[[#fn:r715|715]]</sup> ; Johnston et al., 2019 <sup>[[#fn:r716|716]]</sup> ; Rumpf et al., 2019 <sup>[[#fn:r717|717]]</sup> ) ( ''medium agreement'' , ''robust evidence'' ). These responses are often linked directly to warming, yet a changing cryosphere, for example, in the form of decreasing snow thickness or altered seasonality of snow (e.g., Matteodo et al., 2016; Kirkpatrick et al., 2017 <sup>[[#fn:r718|718]]</sup> ; Amagai et al., 2018 <sup>[[#fn:r719|719]]</sup> ; Wu et al., 2018 <sup>[[#fn:r720|720]]</sup> ) or indirectly leading to changes in soil moisture ( Harpold and Molotch, 2015 <sup>[[#fn:r721|721]]</sup> ), can play a significant role for growth, fitness and survival of many species (e.g., Grytnes et al., 2014; Winkler et al., 2016 <sup>[[#fn:r722|722]]</sup> ) ( ''medium evidence, high agreement'' ).

Cryospheric changes were found to be beneficial for some plant species and for ecosystems in some regions, improving a number of ecosystem services, such as by provisioning new habitat for endemic plant species and increasing plant productivity ( ''high confidence'' ). Decreasing snow cover duration, glacier retreat and permafrost thaw have already and will over coming decades allow plant species, including some endemic species, to increase their abundance and extend their range in many mountain ranges (Yang et al., 2010a <sup>[[#fn:r723|723]]</sup> ; Grytnes et al., 2014 <sup>[[#fn:r724|724]]</sup> ; Elsen and Tingley, 2015 <sup>[[#fn:r725|725]]</sup> ; Dolezal et al., 2016 <sup>[[#fn:r726|726]]</sup> ; Wang et al., 2016b <sup>[[#fn:r727|727]]</sup> ; D’Amico et al., 2017 <sup>[[#fn:r728|728]]</sup> ; Liang et al., 2018 <sup>[[#fn:r729|729]]</sup> ; Yang et al., 2018 <sup>[[#fn:r730|730]]</sup> ; You et al., 2018 <sup>[[#fn:r731|731]]</sup> ; He et al., 2019 <sup>[[#fn:r732|732]]</sup> ). Over recent decades, plant colonisation after glacier retreat has been swift, for example, at many sites with favourable soils in the European Alps (Matthews and Vater, 2015 <sup>[[#fn:r733|733]]</sup> ; Fickert and Grüninger, 2018 <sup>[[#fn:r734|734]]</sup> ) or has even accelerated compared to 100 years ago (Fickert et al., 2016 <sup>[[#fn:r735|735]]</sup> ). At other sites of the European Alps (D’Amico et al., 2017) and in other mountain ranges (e.g., Andes and Alaska; Darcy et al., 2018 <sup>[[#fn:r736|736]]</sup> ; Zimmer et al., 2018 <sup>[[#fn:r737|737]]</sup> ) the rate of colonisation remains slow due to soil type, soil formation and phosphorous limitation (Darcy et al., 2018 <sup>[[#fn:r738|738]]</sup> ). In Bhutan, snowlines have ascended and new plant species have established themselves in these areas, yet despite range expansion and increased productivity, yak herders describe impacts on the ecosystem services as mostly negative (Wangchuk and Wangdi, 2018 <sup>[[#fn:r739|739]]</sup> ). Earlier snowmelt often leads to earlier plant growth and, provided there is sufficient water, including from underlying permafrost, plant productivity has increased in many alpine regions (e.g., Williams et al., 2015; Yang et al., 2018 <sup>[[#fn:r740|740]]</sup> ). Decreased snow cover duration has led to colonisation of snowbed communities by wide-ranging species in several regions, for example, in the Australian Alps (Pickering et al., 2014 <sup>[[#fn:r741|741]]</sup> ), though this can lead to declines in the abundance of resident species, for example, in the Swiss Alps (Matteodo et al., 2016 <sup>[[#fn:r742|742]]</sup> ).

Cryospheric change in high mountains directly harms some plant species and ecosystems in some regions, degrading a number of ecosystem services, such as maintaining regional and global biodiversity, and some provisioning services, for example, fodder or wood production, in terms of timing and magnitude ( ''high confidence'' ). In mountains, microrefugia (a local environment different from surrounding areas) and isolation have contributed to high plant endemism that increases with elevation (Steinbauer et al., 2016 <sup>[[#fn:r743|743]]</sup> ; Zhang and Zhang, 2017 <sup>[[#fn:r744|744]]</sup> ; Muellner-Riehl, 2019 <sup>[[#fn:r745|745]]</sup> ). Microrefugia may enable alpine species to persist if global warming remains below 2˚C relative pre-industrial levels (Scherrer and Körner, 2011 <sup>[[#fn:r746|746]]</sup> ; Hannah et al., 2014 <sup>[[#fn:r747|747]]</sup> ; Graae et al., 2018 <sup>[[#fn:r748|748]]</sup> ) ( ''medium evidence'' , ''medium agreement'' ). Yet, where glaciers have been retreating over recent decades, cool microrefugia have shifted location or decreased in extent ( Gentili et al., 2015 <sup>[[#fn:r749|749]]</sup> ). In regions with insufficient summer precipitation, earlier snowmelt and absence of permafrost lead to insufficient water supply during the growing season, and consequently an earlier end of peak season, altered species composition, and a decline in greenness or productivity ( Trujillo et al., 2012 <sup>[[#fn:r750|750]]</sup> ; Sloat et al., 2015 <sup>[[#fn:r751|751]]</sup> ; Williams et al., 2015 <sup>[[#fn:r752|752]]</sup> ; Yang et al., 2018 <sup>[[#fn:r753|753]]</sup> ) ( ''medium evidence'' , ''high agreement'' ). Across elevations, alpine-restricted species show greater sensitivity to the timing of snowmelt than wide ranging species ( Lesica, 2014 <sup>[[#fn:r754|754]]</sup> ; Winkler et al., 2018 <sup>[[#fn:r755|755]]</sup> ), and though the cause is often not known, some alpine-restricted species have declined in abundance or disappeared in regions with distinctive flora ( Evangelista et al., 2016 <sup>[[#fn:r756|756]]</sup> ; Giménez-Benavides et al., 2018 <sup>[[#fn:r757|757]]</sup> ; Lamprecht et al., 2018 <sup>[[#fn:r758|758]]</sup> ; Panetta et al., 2018 <sup>[[#fn:r759|759]]</sup> ) ( ''medium evidence, high agreement'' ).

The shrinking cryosphere represents a loss of critical habitat for wildlife that depend on snow and ice cover, affecting well-known and unique high-elevation species ( ''high confidence'' ). Areas with seasonal snow and glaciers are essential habitat for birds and mammals within mountain ecosystems for foraging, relief from climate stress, food caching and nesting grounds ( Hall et al., 2016 <sup>[[#fn:r760|760]]</sup> ; Rosvold, 2016 <sup>[[#fn:r761|761]]</sup> ) ( ''robust evidence'' ). Above 5,000 m a.s.l. in Peru, there was recently a first observation of bird nesting for which its nesting may be glacier obligate ( Hardy et al., 2018 <sup>[[#fn:r762|762]]</sup> ). The insulated and thermally stable region under the snow at the soil-snow interface, termed the subnivean, has been affected by changing snowpack, limiting winter activity and decreasing population growth for some mountain animals, including frogs, rodents and small carnivores (Penczykowski et al., 2017 <sup>[[#fn:r763|763]]</sup> ; Zuckerberg and Pauli, 2018 <sup>[[#fn:r764|764]]</sup> ; Kissel et al., 2019 <sup>[[#fn:r765|765]]</sup> ) ( ''medium evidence'' ). Many mountain animals have been observed to change their behaviour in a subtle manner, for example., in foraging or hunting behaviour, due to cryospheric changes (e.g., Rosvold, 2016; Büntgen et al., 2017 <sup>[[#fn:r766|766]]</sup> ; Mahoney et al., 2018 <sup>[[#fn:r767|767]]</sup> ) ( ''medium evidence'' , ''high agreement'' ). In the Canadian Rocky Mountains, grizzly bears have moved to new snow free habitat after emerging in spring from hibernation to dig for forage, which may increase the risk of human-bear encounters (Berman et al., 2019 <sup>[[#fn:r768|768]]</sup> ). In the US Central Rocky Mountains, migratory herbivores, such as elk, moose and bison, track newly emergent vegetation that greens soon after snowmelt (Merkle et al., 2016 <sup>[[#fn:r769|769]]</sup> ). For elk, this was found to increase fat gain (Middleton et al., 2018 <sup>[[#fn:r770|770]]</sup> ). Due to loss of snow patches that increase surface water and thus insect abundance, some mammal species, for example, reindeer and ibex, have changed their foraging behaviour to evade the biting insects with negative impacts on reproductive fitness (Vors and Boyce, 2009 <sup>[[#fn:r771|771]]</sup> ; Büntgen et al., 2017 <sup>[[#fn:r772|772]]</sup> ).

Many endemic plant and animal species including mammals and invertebrates in high mountain regions are vulnerable to further decreasing snow cover duration, such as later onset of snow accumulation and/or earlier snowmelt ( ''high confidence'' ) ( Williams et al., 2015 <sup>[[#fn:r773|773]]</sup> ; Slatyer et al., 2017 <sup>[[#fn:r774|774]]</sup> ). Winter-white animals for which coat or plumage colour is cued by day length will confront more days with brown snowless ground (Zimova et al., 2018 <sup>[[#fn:r775|775]]</sup> ), which has already contributed to range contractions for several species, including hares and ptarmigan (Imperio et al., 2013 <sup>[[#fn:r776|776]]</sup> ; Sultaire et al., 2016 <sup>[[#fn:r777|777]]</sup> ; Pedersen et al., 2017 <sup>[[#fn:r778|778]]</sup> ) ( ''robust evidence'' ). Under all climate scenarios, the duration of this camouflage mismatch will increase, enhancing predation rates thereby decreasing populations of coat-colour changing species (e.g., 24% decrease by late century under RCP8.5 for snowshoe hares; Zimova et al., 2016 <sup>[[#fn:r779|779]]</sup> ; see also Atmeh et al., 2018) ( ''medium evidence'' , ''high agreement'' ). For roe deer (Plard et al., 2014 <sup>[[#fn:r780|780]]</sup> ) and mountain goats (White et al., 2017 <sup>[[#fn:r781|781]]</sup> ), climate driven changes in snowmelt duration and summer temperatures will reduce survival considerably under RCP4.5 and RCP8.5 scenarios ( ''medium'' ''evidence'' , ''high agreement'' ).

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