Editing IPCC:AR6/WGII/Cross-Chapter-Paper-5 (section)

=== Box CCP5.1 | Wildfires and Mountain Ecosystems ===

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''Mountain ecosystems have long been known to be highly sensitive to the direct impacts of climatic warming and drying ( [[#Beniston--1994|Beniston et al., 1994]] ; [[#Nogués-Bravo--2009|Nogués-Bravo, 2009]] ; [[#Gottfried--2012|Gottfried et al., 2012]] ; [[#Guisan--2019|Guisan et al., 2019]] ). Furthermore, wildfires in these ecosystems, as in many others (Sections 2.4.4.2 and 2.5.3.2), are also expected to increase ( [[#Abatzoglou--2019|Abatzoglou et al., 2019]] ). This is because the occurrence and severity of fire are governed by four fundamental processes that are intricately linked to climate: 1) fuel biomass growth, 2) fuel moisture and type, 3) ignition source and 4) favourable weather conditions for fire spread ( [[#Bradstock--2010|Bradstock, 2010]] ).''

''In temperate and tropical mountain ecosystems, increases in fire activity are potentially linked to changing climate on most continents, including Europe ( [[#Dupire--2017|Dupire et al., 2017]] ), North America ( [[#Westerling--2016|Westerling, 2016]] ; [[#Halofsky--2020|Halofsky et al., 2020]] ; [[#Burke--2021|Burke et al., 2021]] ), South America ( [[#Román-Cuesta--2014|Román-Cuesta et al., 2014]] ), Africa ( [[#Hemp--2005|Hemp, 2005]] ), Asia ( [[#Tian--2014|Tian et al., 2014]] ) and Australia ( [[#Bradstock--2014|Bradstock et al., 2014]] ; [[#Abram--2021|Abram et al., 2021]] ). In these ecosystems, fire frequency, severity and extent (i.e., the fire regime) are increasing because of climate-induced impacts on fuel moisture ( [[#Gergel--2017|Gergel et al., 2017]] ; [[#Littell--2018|Littell et al., 2018]] ), vegetation composition (i.e., fuel types) ( [[#Camac--2017|Camac et al., 2017]] ; [[#Prichard--2017|Prichard et al., 2017]] ; [[#Zylstra--2018|Zylstra, 2018]] ), fire-conducive weather patterns and the length of fire seasons ( [[#Westerling--2016|Westerling, 2016]] ; [[#Fill--2019|Fill et al., 2019]] ; [[#Di%20Virgilio--2020|Di Virgilio et al., 2020]] ).''

''Fire in mountain ecosystems alters many ecological processes and ecosystem services across all elevational zones, from foothill montane forests to high-elevation alpine (treeless) zones ( [[#Turner--2003|Turner et al., 2003]] ; [[#Williams--2008|Williams et al., 2008]] ; [[#Oliveras--2014|Oliveras et al., 2014]] , 2018; [[#Rocca--2014|Rocca et al., 2014]] ). However, the magnitude of short-term and long-term fire impacts depends on the degree of novelty of future fire regimes and the capacity of species to adapt to change ( [[#Camac--2017|Camac et al., 2017]] , 2021; [[#Archibald--2018|Archibald et al., 2018]] ).''

''Montane and sub-alpine ecosystems have variable ecological responses to fire that are ultimately influenced by long-term, historical fire regimes and the evolutionary forces that have governed post-fire regeneration strategies of the biota. Two contrasting strategies in temperate forests are illustrated here. SE Australian mountain ash ('' ''Eucalyptus regnans'' '') forests are adapted to a high-severity fire regime, consisting of infrequent (&gt;100 years), large stand-replacing wildfires ( [[#Bowman--2016|Bowman et al., 2016]] ). Mountain ash is a long-lived obligate seeder but is slow to reach reproductive maturity (&gt;20 years) ( [[#Bowman--2016|Bowman et al., 2016]] ). As such, natural post-fire regeneration takes decades to centuries to recover to pre-fire conditions, and if fire reoccurs before reproductive maturity is reached, the species can be eliminated. By contrast, ponderosa pine ('' ''Pinus ponderosa'' '') forests of the SW United States have evolved with a low- or mixed-severity fire regime, where fire is frequent (5–25 years), of low intensity, less likely to kill dominant stands and, thus, allow faster post-fire recovery ( [[#Prichard--2017|Prichard et al., 2017]] ). However, post-fire recovery times in this ecosystem are also becoming longer due to a century of effective fire suppression, shifting the fire regime to one which is more infrequent, of high intensity, extensive and stand replacing ( [[#Prichard--2017|Prichard et al., 2017]] ).''

''Above the treeline, fire is less common than in foothill forests. Post-fire recovery times also tend to be shorter ( [[#Williams--2008|Williams et al., 2008]] ; [[#Camac--2013|Camac et al., 2013]] ; [[#Verrall--2019|Verrall and Pickering, 2019]] ) because of the dual influences of low flammability traits coupled with the fact that most alpine plant species exhibit strong resprouting strategies that have evolved in response to harsh climate conditions ( [[#Körner--2003|Körner, 2003]] ). However, fires in alpine treeless landscapes can still have long-term and catastrophic impacts on fire-sensitive vegetation types such as groundwater-dependent wetlands dominated by hygrophilous plants and peat soils ( [[#De%20Roos--2018|De Roos et al., 2018]] ). Similar impacts can be severe on long-lived, slow-growing vegetation such as coniferous heathlands ( [[#Bowman--2019|Bowman et al., 2019]] ) and highly restricted and threatened fauna (e.g., mountain pygmy possum) that depend on these plant communities ( [[#Gibson--2018|Gibson et al., 2018]] ). Such fires have even been found to significantly impact sub-alpine treeline mortality rates ( [[#Fairman--2017|Fairman et al., 2017]] ) and in some cases have resulted in treelines shifting to lower elevations (e.g., [[#Hemp--2005|Hemp, 2005]] ).''

The long-term implications of a warmer global climate, coupled with more frequent and/or severe fires in mountain ecosystems, are expected to be transformative for mountain biota. Fire-sensitive montane forests, such as Australia’s alpine ash ( ''Eucalyptus delegatensis'' ), are expected to become highly susceptible to population collapse and local extinction as intervals between fire events contract and become too short for species to reach reproductive maturity ( [[#Bowman--2014|Bowman et al., 2014]] ; [[#Enright--2015|Enright et al., 2015]] )—an impact that will ''likely'' be further exacerbated by recruitment failure caused by post-fire drought and moisture deficiencies ( [[#Davies--2019|Davies et al., 2019]] ; [[#Halofsky--2020|Halofsky et al., 2020]] ; [[#Rodman--2020|Rodman et al., 2020]] ). Fire and climate change are also ''likely'' to act synergistically in mountainous ecosystems, via positive feedbacks that increase fire frequency by changing vegetation composition to more flammable fuel types, thereby increasing landscape susceptibility to future fire ( [[#Camac--2017|Camac et al., 2017]] ; [[#Tepley--2018|Tepley et al., 2018]] ; [[#Zylstra--2018|Zylstra, 2018]] ; [[#Lucas--2021|Lucas and Harris, 2021]] ). More frequent fires in these ecosystems will also exacerbate native and exotic species invasions ( [[#Catford--2009|Catford et al., 2009]] ; [[#McDougall--2011|McDougall et al., 2011]] ; [[#Gottfried--2012|Gottfried et al., 2012]] ; [[#Kueffer--2013|Kueffer et al., 2013]] ), faunal population declines ( [[#Ward--2020|Ward et al., 2020]] ), poor air quality ( [[#de%20la%20Barrera--2018|de la Barrera et al., 2018]] ; [[#Burke--2021|Burke et al., 2021]] ) and soil erosion and landslide risk ( [[#de%20la%20Barrera--2018|de la Barrera et al., 2018]] ) and reduce freshwater catchment volumes and quality ( [[#Rust--2018|Rust et al., 2018]] ; [[#Niemeyer--2020|Niemeyer et al., 2020]] ), all of which will impact negatively on human health and well-being ( [[#Ebi--2021|Ebi et al., 2021]] ).

''Taken together, this evidence suggests that a significant risk exists of wildfire exacerbating other impacts of climate change on already vulnerable ecosystems in many mountain regions ('' ''medium confidence'' '').''

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