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

==== 5.5.3.1 Impacts on rangelands, feeds and forages ====

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Uncertainties persist regarding estimates of net primary productivity (NPP) in grazing lands ( [[#Fetzel--2017|Fetzel et al., 2017]] ; [[#Chen--2018b|Chen et al., 2018b]] ), so estimation of climate change impacts on grasslands is challenging. Mean global annual NPP is projected to decline 10 gC m −2 yr −1 in 2050 under RCP8.5, although herbaceous NPP is projected to increase slightly ( [[#Boone--2018|Boone et al., 2018]] ; see Figure 5.11). Similar estimates were made by [[#Havlik--2014|Havlik et al. (2014)]] : large increases in projected NPP in higher northern latitudes (21% increase in the USA and Canada) and large declines in western Africa (−46%) and Australia (−17%). The cumulative effects of impacts on forage productivity globally are projected to result in 7–10% declines in livestock numbers by 2050 for warming of ~2°C, representing a loss of livestock assets ranging from USD 10 to 13 billion ( [[#Boone--2018|Boone et al., 2018]] ). Changes to African grassland productivity will have substantial, negative impacts on the livelihoods of &gt;180 million people.

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[[File:bbbc672a5e564302999be245928fdce7 IPCC_AR6_WGII_Figure_5_011.png]]

'''Figure 5.11 |''' '''Regional percent changes in land cover and soil carbon from ensemble simulation results in 2050 under emissions scenario RCP8''' '''.''' '''5 compared with 1971–2000.''' Plant responses were enhanced by CO 2 fertilisation. The larger chart (lower left) shows mean changes for all rangelands, and all charts are scaled to −60% to +60% change. Shown are annual net primary productivity (ANPP), herbaceous net primary productivity (HNPP), bare ground, herbaceous (herb), shrub, and tree cover, SOC (soil carbon), above-ground live biomass and below-ground live biomass. Regions as defined by the United Nations Statistics Division. The bar for above-ground live biomass in Western Asia (*) is truncated and is 82% ( [[#Boone--2018|Boone et al., 2018]] ).

Increases in above-ground NPP, and woody cover at the expense of grassland, are projected in some of the tropical and subtropical drylands ( [[#Doherty--2010|Doherty et al., 2010]] ; [[#Ravi--2010|Ravi et al., 2010]] ; [[#Saki--2018|Saki et al., 2018]] ), in Mediterranean wood pastures ( [[#Rolo--2019|Rolo and Moreno, 2019]] ) and in the northern Great Plains of North America ( [[#Klemm--2020|Klemm et al., 2020]] ). [[#Godde--2021|Godde et al. (2021)]] projected that woody encroachment would occur on 51% of global rangeland area by 2050 under RCP8.5. The future makeup of grasslands under climate change is uncertain, given the variation in responses of the component species, though this variation may provide a climate buffer ( [[#Jones--2019|Jones, 2019]] ) ( ''low confidence'' ). C4 grass species are regarded as less responsive to elevated carbon dioxide than C3 species, though this is not always the case ( [[#Reich--2018|Reich et al., 2018]] ).

There are other interactions between climate change and grazing effects on grasslands. Li (2018a) reported strong negative responses of NPP and species richness to 4°C warming, a 50% precipitation decrease, and high grazing intensity. Changes in grassland composition will inevitably change their suitability for different grazing animal species, with switches from herbaceous grazers such as cattle to goats and camels to take advantage of increases in shrubland ( [[#Kagunyu--2014|Kagunyu and Wanjohi, 2014]] ). Rangeland feed quality may also be reduced via invasive species of lower quality than native species ( [[#Blumenthal--2016|Blumenthal et al., 2016]] ).

Warming and water deficits impair the quality and digestibility of a C4 tropical forage grass, ''Panicum maximum'' , because of increases in leaf lignin ( [[#Habermann--2019|Habermann et al., 2019]] ). A metanalysis by Dellar (2018) of climate change impacts on European pasture yield and quality found an increase in above-ground dry weight under increased CO 2 concentrations for forbs, legumes, graminoids and shrubs with reductions in N concentrations in all plant functional groups. Temperature increases will increase yields in alpine and northern areas (+82.6%) but reduce N concentrations for shrubs (−13.6%) and forbs (−18.5%).

Increased temperatures and CO 2 concentrations may increase herbaceous growth and favour legumes over grasses in mixed pastures ( [[#He--2019|He et al., 2019]] ). These effects may be modified by changes in rainfall patterns, plant competition, perennial growth habits and plant–animal interactions. The cumulative effect of these factors is uncertain. Large, persistent declines in forage quality are projected, irrespective of warming, under elevated CO 2 conditions (600 ppm and +1.5°C day/3°C night temperature increases) in North American grasslands ( [[#Augustine--2018|Augustine et al., 2018]] ). Rising CO 2 concentrations may result in losses of iron, zinc and protein in plants by up to 8% by 2050 ( [[#Smith--2018|Smith and Myers, 2018]] ). Little information is available on possible impacts on carbon-based micronutrients, such as vitamins. About 57% of grasses globally are C3 plants and thus susceptible to CO 2 effects on their nutritional quality ( [[#Osborne--2014|Osborne et al., 2014]] ). These impacts will result in greater nutritional stress in grazing animals as well as reduced meat and milk production (quality and quantity) ( ''high confidence'' , ''medium evidence'' ).

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