Editing IPCC:AR6/SRCCL/Chapter-3 (section)

=== 3.7.3 Invasive plant species ===

<div id="section-3-7-3-1-introduction"></div>

<span id="introduction-1"></span>
==== 3.7.3.1 Introduction ====

<div id="section-3-7-3-1-introduction-block-1"></div>

The spread of invasive plants can be exacerbated by climate change (Bradley et al. 2010 <sup>[[#fn:r1603|1603]]</sup> ; Davis et al. 2000 <sup>[[#fn:r1604|1604]]</sup> ). In general, it is expected that the distribution of invasive plant species with high tolerance to drought or high temperatures may increase under most climate change scenarios ( ''medium to high confidence'' ) (Bradley et al. 2010 <sup>[[#fn:r1605|1605]]</sup> ; Settele et al. 2014 <sup>[[#fn:r1606|1606]]</sup> ; Scasta et al. 2015 <sup>[[#fn:r1607|1607]]</sup> ). Invasive plants are considered a major risk to native biodiversity and can disturb the nutrient dynamics and water balance in affected ecosystems (Ehrenfeld 2003 <sup>[[#fn:r1608|1608]]</sup> ). Compared to more humid regions, the number of species that succeed in invading dryland areas is low (Bradley et al. 2012 <sup>[[#fn:r1609|1609]]</sup> ), yet they have a considerable impact on biodiversity and ecosystem services (Le Maitre et al. 2015, 2011; Newton et al. 2011 <sup>[[#fn:r1610|1610]]</sup> ). Moreover, human activities in dryland areas are responsible for creating new invasion opportunities (Safriel et al. 2005 <sup>[[#fn:r1611|1611]]</sup> ).

Current drivers of species introductions include expanding global trade and travel, land degradation and changes in climate (Chytrý et al. 2012 <sup>[[#fn:r1612|1612]]</sup> ; Richardson et al. 2011 <sup>[[#fn:r1613|1613]]</sup> ; Seebens et al. 2018 <sup>[[#fn:r1614|1614]]</sup> ). For example, Davis et al. (2000) suggests that high rainfall variability promotes the success of alien plant species – as reported for semi-arid grasslands and Mediterranean-type ecosystems (Cassidy et al. 2004 <sup>[[#fn:r1615|1615]]</sup> ; Reynolds et al. 2004 <sup>[[#fn:r1616|1616]]</sup> ; Sala et al. 2006 <sup>[[#fn:r1617|1617]]</sup> ). Furthermore, Panda et al. (2018) demonstrated that many invasive species could withstand elevated temperature and moisture scarcity caused by climate change. Dukes et al. (2011) observed that the invasive plant yellow-star thistle ( ''Centaurea solstitialis'' ) grew six time larger under the elevated atmospheric CO <sub>2</sub> expected in future climate change scenarios.

Climate change is ''likely'' to aggravate the problem as existing species continue to spread unabated and other species develop invasive characteristics (Hellmann et al. 2008 <sup>[[#fn:r1619|1619]]</sup> ). Although the effects of climate change on invasive species distributions have been relatively well explored, the greater impact on ecosystems is less well understood (Bradley et al. 2010 <sup>[[#fn:r1620|1620]]</sup> ; Eldridge et al. 2011 <sup>[[#fn:r1621|1621]]</sup> ).

Due to the time lag between the initial release of invasive species and their impact, the consequence of invasions is not immediately detected and may only be noticed centuries after introduction (Rouget et al. 2016 <sup>[[#fn:r1622|1622]]</sup> ). Climate change and invading species may act in concert (Bellard et al. 2013 <sup>[[#fn:r1623|1623]]</sup> ; Hellmann et al. 2008 <sup>[[#fn:r1625|1625]]</sup> ; Seebens et al. 2015 <sup>[[#fn:r1626|1626]]</sup> ). For example, invasion often changes the size and structure of fuel loads, which can lead to an increase in the frequency and intensity of fire (Evans et al. 2015). In areas where the climate is becoming warmer, an increase in the likelihood of suitable weather conditions for fire may promote invasive species, which in turn may lead to further desertification. Conversely, fire may promote plant invasions via several mechanisms (by reducing cover of competing vegetation, destroying native vegetation and clearing a path for invasive plants or creating favourable soil conditions) (Brooks et al. 2004 <sup>[[#fn:r1627|1627]]</sup> ; Grace et al. 2001 <sup>[[#fn:r1628|1628]]</sup> ; Keeley and Brennan 2012 <sup>[[#fn:r1629|1629]]</sup> ).

<div id="section-3-7-3-1-introduction-block-2"></div>

<span id="figure-3.14"></span>
<!-- START IMG -->
<!-- IMG TITLE -->
'''Figure 3.14'''

<span id="difference-between-the-number-of-invasive-alien-species-n99-from-bellard-et-al.-2013-predicted-to-occur-by-2050-under-a1b-scenario-and-current-period-2000-within-the-dryland-areas"></span>
<!-- IMG CAPTION -->
'''Difference between the number of invasive alien species (n=99, from Bellard et al. (2013)) predicted to occur by 2050 (under A1B scenario) and current period ‘2000’ within the dryland areas'''
<!-- IMG FILE -->
[[File:f7e78c29625c2d159d611f7fff53955a Figure-3.14.png]]

Difference between the number of invasive alien species (n=99, from Bellard et al. (2013) <sup>[[#fn:r1808|1808]]</sup> ) predicted to occur by 2050 (under A1B scenario) and current period ‘2000’ within the dryland areas

<!-- END IMG -->
<div id="section-3-7-3-1-introduction-block-3"></div>

At a regional scale, Bellard et al. (2013) <sup>[[#fn:r1809|1809]]</sup> predicted increasing risk in Africa and Asia, with declining risk in Australia (Figure 3.14). This projection does not represent an exhaustive list of invasive alien species occurring in drylands.

A set of four case studies in Ethiopia, Mexico, the USA and Pakistan is presented below to describe the nuanced nature of invading plant species, their impact on drylands and their relationship with climate change.

<div id="section-3-7-3-2-ethiopia"></div>

<span id="ethiopia"></span>
==== 3.7.3.2 Ethiopia ====

<div id="section-3-7-3-2-ethiopia-block-1"></div>

The two invasive plants that inflict the heaviest damage to ecosystems, especially biodiversity, are the annual herbaceous weed, ''Parthenium hysterophorus'' ( ''Asteraceae'' ) also known as Congress weed; and the tree species, ''Prosopis juliflora (Fabaceae'' ) also called Mesquite, both originating from the southwestern United States to Central/South America (Adkins and Shabbir 2014 <sup>[[#fn:r1630|1630]]</sup> ). ''Prosopis'' was introduced in the 1970s and has since spread rapidly. ''Prosopis'' , classified as the highest priority invader in Ethiopia, is threatening livestock production and challenging the sustainability of the pastoral systems. ''Parthenium'' is believed to have been introduced along with relief aid during the debilitating droughts of the early 1980s, and a recent study reported that it has spread into 32 out of 34 districts in Tigray, the northernmost region of Ethiopia (Teka 2016 <sup>[[#fn:r1631|1631]]</sup> ). A study by Etana et al. (2011) indicated that Parthenium caused a 69% decline in the density of herbaceous species in Awash National Park within a few years of introduction. In the presence of Parthenium, the growth and development of crops is suppressed due to its allelopathic properties. McConnachie et al. (2011) estimated a 28% crop loss across the country, including a 40–90% reduction in sorghum yield in eastern Ethiopia alone (Tamado et al. 2002 <sup>[[#fn:r1632|1632]]</sup> ). The weed is a substantial agricultural and natural resource problem and constitutes a significant health hazard (Fasil 2011). Parthenium causes acute allergic respiratory problems, skin dermatitis, and reportedly mutagenicity both in humans and livestock (Mekonnen 2017; Patel 2011 <sup>[[#fn:r1633|1633]]</sup> ). The eastern belt of Africa – including Ethiopia – presents a very suitable habitat, and the weed is expected to spread further in the region in the future (Mainali et al. 2015 <sup>[[#fn:r1635|1635]]</sup> ).

There is neither a comprehensive intervention plan nor a clear institutional mandate to deal with invasive weeds, however, there are fragmented efforts involving local communities even though they are clearly inadequate. The lessons learned, related to actions that have contributed to the current scenario, are several. First, lack of coordination and awareness – mesquite was introduced by development agencies as a drought-tolerant shade tree with little consideration of its invasive nature. If research and development institutions had been aware, a containment strategy could have been implemented early on. The second major lesson is the cost of inaction. When research and development organisations did sound the alarm, the warnings went largely unheeded, resulting in the spread and buildup of two of the worst invasive plant species in the world (Fasil 2011 <sup>[[#fn:r1636|1636]]</sup> ).

<div id="section-3-7-3-3-mexico"></div>

<span id="mexico"></span>
==== 3.7.3.3 Mexico ====

<div id="section-3-7-3-3-mexico-block-1"></div>

Buffelgrass ( ''Cenchrus ciliaris'' L.), a native species from southern Asia and East Africa, was introduced into Texas and northern Mexico in the 1930s and 1940s, as it is highly productive in drought conditions (Cox et al. 1988; Rao et al. 1996). In the Sonoran desert of Mexico, the distribution of buffelgrass has increased exponentially, covering 1 Mha in Sonora State (Castellanos-Villegas et al. 2002 <sup>[[#fn:r1637|1637]]</sup> ). Furthermore, its potential distribution extended to 53% of Sonora State and 12% of semi-arid and arid ecosystems in Mexico (Arriaga et al. 2004 <sup>[[#fn:r1638|1638]]</sup> ). Buffelgrass has also been reported as an aggressive invader in Australia and the USA, resulting in altered fire cycles that enhance further spread of this plant and disrupt ecosystem processes (Marshall et al. 2012 <sup>[[#fn:r1639|1639]]</sup> ; Miller et al. 2010 <sup>[[#fn:r1641|1641]]</sup> ; Schlesinger et al. 2013 <sup>[[#fn:r1642|1642]]</sup> ).

Castellanos et al. (2016) reported that soil moisture was lower in the buffelgrass savannah cleared 35 years ago than in the native semi-arid shrubland, mainly during the summer. The ecohydrological changes induced by buffelgrass can therefore displace native plant species over the long term. Invasion by buffelgrass can also affect landscape productivity, as it is not as productive as native vegetation (Franklin and Molina-Freaner 2010 <sup>[[#fn:r1643|1643]]</sup> ). Incorporation of buffelgrass is considered a good management practice by producers and the government. For this reason, no remedial actions are undertaken.

<div id="section-3-7-3-4-united-states-of-america"></div>

<span id="united-states-of-america"></span>
==== 3.7.3.4 United States of America ====

<div id="section-3-7-3-4-united-states-of-america-block-1"></div>

Sagebrush ecosystems have declined from 25 Mha to 13 Mha since the late 1800s (Miller et al. 2011 <sup>[[#fn:r1644|1644]]</sup> ). A major cause is the introduction of non-native cheatgrass ( ''Bromus tectorum'' ), which is the most prolific invasive plant in the USA. Cheatgrass infests more than 10 Mha in the Great Basin and is expanding every year (Balch et al. 2013 <sup>[[#fn:r1645|1645]]</sup> ). It provides a fine-textured fuel that increases the intensity, frequency and spatial extent of fire (Balch et al. 2013). Historically, wildfire frequency was 60 to 110 years in Wyoming big sagebrush communities and has increased to five years following the introduction of cheatgrass (Balch et al. 2013 <sup>[[#fn:r1646|1646]]</sup> ; Pilliod et al. 2017 <sup>[[#fn:r1648|1648]]</sup> ).

The conversion of the sagebrush steppe biome to annual grassland with higher fire frequencies has severely impacted livestock producers, as grazing is not possible for a minimum of two years after fire. Furthermore, cheatgrass and wildfires reduce critical habitat for wildlife and negatively impact species richness and abundance – for example, the greater sage-grouse ( ''Centocercus urophasianus'' ) and pygmy rabbit ( ''Brachylagus idahoensis'' ) which are on the verge of being listed for federal protection (Crawford et al. 2004 <sup>[[#fn:r1649|1649]]</sup> ; Larrucea and Brussard 2008 <sup>[[#fn:r1650|1650]]</sup> ; Lockyer et al. 2015 <sup>[[#fn:r1651|1651]]</sup> ).

Attempts to reduce cheatgrass impacts through reseeding of both native and adapted introduced species have occurred for more than 60 years (Hull and Stewart 1949 <sup>[[#fn:r1652|1652]]</sup> ) with little success. Following fire, cheatgrass becomes dominant and recovery of native shrubs and grasses is improbable, particularly in relatively low-elevation sites with minimal annual precipitation (less than 200 mm yr <sup>–1</sup> ) (Davies et al. 2012 <sup>[[#fn:r1653|1653]]</sup> ; Taylor et al. 2014 <sup>[[#fn:r1654|1654]]</sup> ). Current rehabilitation efforts emphasise the use of native and non-native perennial grasses, forbs and shrubs (Bureau of Land Management 2005 <sup>[[#fn:r1655|1655]]</sup> ). Recent literature suggests that these treatments are not consistently effective at displacing cheatgrass populations or re-establishing sage-grouse habitat, with success varying with elevation and precipitation (Arkle et al. 2014 <sup>[[#fn:r1656|1656]]</sup> ; Knutson et al. 2014 <sup>[[#fn:r1657|1657]]</sup> ). Proper post-fire grazing rest, season-of-use, stocking rates, and subsequent management are essential to restore resilient sagebrush ecosystems before they cross a threshold and become an annual grassland (Chambers et al. 2014 <sup>[[#fn:r1658|1658]]</sup> ; Miller et al. 2011 <sup>[[#fn:r1659|1659]]</sup> ; Pellant et al. 2004 <sup>[[#fn:r1660|1660]]</sup> ). Biological soil crust protection may be an effective measure to reduce cheatgrass germination, as biocrust disturbance has been shown to be a key factor promoting germination of non-native grasses (Hernandez and Sandquist 2011). Projections of increasing temperature (Abatzoglou and Kolden 2011 <sup>[[#fn:r1662|1662]]</sup> ), and observed reductions in and earlier melting of snowpack in the Great Basin region (Harpold and Brooks 2018 <sup>[[#fn:r1663|1663]]</sup> ; Mote et al. 2005 <sup>[[#fn:r1664|1664]]</sup> ) suggest that there is a need to understand current and past climatic variability as this will drive wildfire variability and invasions of annual grasses.

<div id="section-3-7-3-5-pakistan"></div>

<span id="pakistan"></span>
==== 3.7.3.5 Pakistan ====

<div id="section-3-7-3-5-pakistan-block-1"></div>

The alien plants invading local vegetation in Pakistan include ''Brossentia papyrifera'' (found in Islamabad Capital territory), ''Parthenium hysterophorus'' (found in Punjab and Khyber Pakhtunkhwa provinces), ''Prosopis juliflora'' (found all over Pakistan), ''Eucalyptus camaldulensis'' (found in Punjab and Sindh provinces), ''Salvinia'' (aquatic plant widely distributed in water bodies in Sindh), ''Cannabis sativa'' (found in Islamabad Capital Territory), ''Lantana camara'' and ''Xanthium strumarium'' (found in upper Punjab and Khyber Pakhtunkhwa provinces) (Khan et al. 2010 <sup>[[#fn:r1665|1665]]</sup> ; Qureshi et al. 2014 <sup>[[#fn:r1666|1666]]</sup> ). Most of these plants were introduced by the Forest Department decades ago for filling the gap between demand and supply of timber, fuelwood and fodder. These non-native plants have some uses but their disadvantages outweigh their benefits (Marwat et al. 2010 <sup>[[#fn:r1667|1667]]</sup> ; Rashid et al. 2014 <sup>[[#fn:r1668|1668]]</sup> ).

Besides being a source of biological pollution and a threat to biodiversity and habitat loss, the alien plants reduce the land value and cause huge losses to agricultural communities (Rashid et al. 2014 <sup>[[#fn:r1810|1810]]</sup> ). ''Brossentia papyrifera'' , commonly known as Paper Mulberry, is the root cause of inhalant pollen allergy for the residents of lush green Islamabad during spring. From February to April, the pollen allergy is at its peak, with symptoms of severe persistent coughing, difficulty in breathing, and wheezing. The pollen count, although variable at different times and days, can be as high as 55,000 m <sup>-3</sup> .

Early symptoms of the allergy include sneezing, itching in the eyes and skin, and blocked nose. With changing climate, the onset of disease is getting earlier, and pollen count is estimated to cross 55,000 m <sup>–3</sup> (Rashid et al. 2014 <sup>[[#fn:r1670|1670]]</sup> ). About 45% of allergic patients in the twin cities of Islamabad and Rawalpindi showed positive sensitivity to the pollens (Marwat et al. 2010 <sup>[[#fn:r1671|1671]]</sup> ). Millions of rupees have been spent by the Capital Development Authority on pruning and cutting of Paper Mulberry trees but because of its regeneration capacity growth is regained rapidly (Rashid et al. 2014 <sup>[[#fn:r1672|1672]]</sup> ). Among other invading plants, ''Prosopis juliflora'' has allelopathic properties, and ''Eucalyptus'' is known to transpire huge amounts of water and deplete the soil of its nutrient elements (Qureshi et al. 2014 <sup>[[#fn:r1673|1673]]</sup> ).

Although a Biodiversity Action Plan exists in Pakistan, it is not implemented in letter or spirit. The Quarantine Department focuses only on pests and pathogens but takes no notice of plant and animal species being imported. Also, there is no provision for checking the possible impacts of imported species on the environment (Rashid et al. 2014 <sup>[[#fn:r1674|1674]]</sup> ) or for carrying out bioassays of active allelopathic compounds of alien plants.

<span id="oases-in-hyper-arid-areas-in-the-arabian-peninsula-and-northern-africa"></span>