Alien plant species of Haenertsburg Village, Limpopo Province, South Africa

It is generally accepted that urbanisation is changing the composition of species, mostly in urban and surrounding areas, through intentional introduction. The South African National Status Report of 2017 on biological invasions has shown that there is a dearth of knowledge about the invasion status of many invasive alien species in many parts of the country, such as the critically threatened vegetation, Woodbush Granite Grassland (WGG) in Limpopo Province. Consequently, the present study investigated the status of alien plants species in WGG. A roadside survey was carried out in Haenertsburg Village and its vicinity. Roads were used as survey units, and the dumpsite was used as a high risk area. A total of 136 species were identified, belonging to 46 botanical families. This study report the occurrence of 72 species which are regulated by the South Africa’s National Environmental Management: Biodiversity Act (NEMBA, Act 10 of 2004). The present study found results signifi cantly different from existing databases (χ 2 = 16.33473, p = .0001). Included in our list are alien species that need urgent eradication: Coreopsis lanceolata L., Cytisus scoparius (L.) Link, Iris pseudacorus L., Pueraria montana (Lour.) Merr, - and Rubus species as NEMBA category 1a species. Illegal dumping of agricultural waste was found to be one of the contributing factors to IAS in the area. Our study shows that Woodbush Granite Grassland is facing a new threat from invasive species.


Introduction
It is widely accepted that invasive alien species cause major environmental impacts (Parker et al. 1999;Hulme 2012;Simberloff et al. 2013;Blackburn et al. 2014;Rumlerová et al. 2016), such as the reduction of native species in the invaded ranges; for example, Delairea odorata (Cape ivy) was found to reduce native grass and forbs in California (Alvarez and Cushman 2002).As a result, there is an increase in the number of invasive alien species (IAS) around the world (Hulme 2011;Hulme et al. 2018), which are introduced either intentionally or unintentionally (Donaldson et al. 2014;Padayachee et al. 2017).This can be attributed to the increased global trade in alien plant species (Bradley et al. 2012).Several studies have established that one major pathway of introduction is through ornamental plants for gardening (Burt et al. 2007;Niemiera and Holle 2009;Hulme et al. 2018).There is a lack of knowledge about the chain of movement of IAS from the garden back into the wild.Rusterholz et al. (2012) indicated that the illegal disposal of garden waste was a potential pathway, as it can become a source for the introduction of IAS into the pristine environment.Furthermore, the conveyance and disposal of garden waste in authorized waste sites creates pathways for IAS to establish and spread (Plaza et al. 2018).Therefore, understanding the mode by which species escape from cultivation back into the wild is important in reducing the spread of IAS (Plaza et al. 2018).
The South African vegetation ranges from savanna through to grasslands (Mucina and Rutherford 2006).Woodbush Granite Grassland (WGG) is a critically threatened vegetation type in Limpopo Province, with more than 90 per cent already transformed and the remainder profoundly disjointed (Mucina and Rutherford 2006).This is by far the highest in South Africa, as the loss of grasslands across South Africa is estimated to be 35 per cent (Reyers et al. 2005).Given that this vegetation type is rapidly disappearing, along with the species it supports, the Limpopo Department of Economic Development, Environment and Tourism (LEDET) has declared WGG as critically endangered (Dzerefos et al. 2017).Taken together, only two per cent protected grassland biomes in South Africa is WGG (Reyers et al. 2005).Similar to most grasslands, WGG faces a wide number of threats including, but not limited to, forestry plantations, agriculture and related activities, and human settlements (O 'Connor 2005;O'Connor and Kuyler 2009).
Invasive alien species are a significant contributor to the many threats faced by WGG (Mucina and Rutherford 2006).However, few studies have been done on the extent and impact of invasive species in WGG (O 'Connor 2005;Mucina and Rutherford 2006).A better understanding of the invasive alien species that pose a major threat to the vegetation type will significantly aid conservation efforts to preserve the WGG (Macdougall and Turkington 2005;Mandle et al. 2011).Dzerefos et al. (2017) reported that, despite the remaining small patches, WGG supports a wide range of life forms, which include over 661 plant species (including 36 that are considered threatened), 237 birds (of which eight are threatened), 62 mammals (of which 19 are threatened), 38 reptiles (of which seven are threatened), and 11 amphibians (of which one is threatened).There are also new additions of recently discovered reptiles and insects, as well as the people who depend on the WGG for their livelihoods.Consequently, the continual loss of WGG could lead to many of the threatened endemic species-such as Aloe lettyae Reynolds and Indigofera rehmannii Baker f.-becoming extinct (O 'Connor 2005;Mucina and Rutherford 2006;Dzerefos et al. 2017).
The role of invasive species as landscape transformers has been welldocumented in some studies (O 'Connor 2005;Mucina and Rutherford 2006;Niemandt and Greve 2016;Dzerefos et al. 2017).A study by Seabloom et al. (2015) postulates that grasslands in most parts of the world are likely to be dominated by IAS.Furthermore, the largest patches of remaining WGG are facing threats from secondary invaders (Mucina and Rutherford 2006;Dzerefos et al. 2017).Research in other parts of the world has demonstrated that grassland ecosystems may be very susceptible to invasive species (Vitousek et al. 1996;MacDougall and Turkington 2005;Pierson et al. 2011), regardless of the grassland occurring within protected areas (Mucina and Rutherford 2006;Dzerefos et al. 2017).However, in South Africa, , there is a dearth of knowledge about the extent and impact of IAS from a South African perspective (Wilson et al. 2013).
The first National Status Report on Biological Invasions of South Africa has shown that there is a dearth of knowledge about the status of invasive alien species (IAS) in many parts of the country (van Wilgen and Wilson 2018).In accordance with the (UNEP [United Nations Environmental Programme] 2002), the Aichi Target 9 states that member states should urgently document the presence of IAS, manage known populations and, where possible, eradicate them.According to Wilson et al. (2013), one of the mandates of the South African National Biodiversity Institute's Directorate of Biological Invasions' early detection and rapid response is to identify potential, current, and future invaders and to eradicate them before they invade larger areas, thus increasing the scope of work and demanding more resources to manage them effectively (Blackburn et al. 2014).There is a national decree to document the occurrence of AIS in the alien and invasive species regulations in the National Environmental Management: Biodiversity Act 10 of 2004 (Biodiversity Act), which is in accordance with the Aichi Biodiversity Targets, established for all signatories to the Convention on Biological Diversity (UNEP [United Nations Environmental Programme] 2002).The convention requires member states to "prevent the introduction of, control or eradicate those alien species which threaten ecosystems, habitats and species" (Article 8(h)).The aim of the present study were to, investigate and record the occurrence of alien plants in Haenertsburg Village, Limpopo Province.

Study site
Haenertsburg Village is at the edge of the great escarpment in Limpopo Province, South Africa, along regional road 71, between the geographical coordinates of 23°54′48.8″Sand 29°56′37.7″E,to the east of Polokwane (Figure 1).The characteristic landscape of the area comprises hills with sandstone outcrops and forest remnants interspersed with grasslands.
According to the Köppen classification as updated by Kottek et al. (2006), Haenertsburg's climate is warm temperate with dry winters (Cwa), characterised by mild temperate with dry winters and warm summers.The annual average temperature is 22 °C.The rainfall, according to the National Meteorology Institute of South Africa (NMISA), is isoigro -i.e., normal rainfall values are well distributed throughout the year.The total human population of Haenertsburg Village is estimated at less than 300 inhabitants.The main economic activities in WGG are forestry and tourism.Activities such as horticulture are regarded as a major global pathway for the introduction of alien plant species (Niemiera and Holle 2009;Hulme et al. 2018).Several studies have demonstrated a positive relationship between human settlement, and the diversity and richness of alien species (Spear et al. 2013;Lewis et al. 2017).For example, a study in New York, USA by Aronson et al. (2015) found that alien species' richness increased along the urbanisation gradient.As a result, some of the plants planted in gardens escape back into the wild and thus become invasive (Marco et al. 2008;Lavergne and Vale 2010;Lubbe et al. 2011).Since human settlement acts as a conduit for alien plant species (Pyšek 1998;Botham et al. 2009;Lososová et al. 2012), research is needed, particularly in small urbanised areas such as Haenertsburg Village.

Data collection
A roadside survey was carried out in Haenertsburg and in the vicinity in February-April 2019 and August-October 2019 on all publicly accessible roads.The roadside survey methodology used in this research was similar to that of other alien plant species surveys (Shuster et al. 2005;Henderson 2006Henderson , 2007;;Wabuyele et al. 2015;Baard and Kraaij 2019;Moshobane et al. 2020a), and has been shown to yield positive and reliable information (Shuster et al. 2005).In this study, the survey units were roadsides (Baard and Kraaij 2019), and included high-risk areas such as streams, dumping sites, school areas, and graveyards.The roads were walked at a top speed of 4 km/hr over a period of 14 days per survey season.
The total sampling effort / time was 224 h (8hr * 28 survey days), and the estimated cost of the survey, excluding salaries, was R41 336.00 (= 2,796.75USD).The status of alien plant species as defined by Richardson et al. (2000) was recorded including those that are garden escapees or plants that escaped cultivation.Species that could not be identified or verified on-site were submitted to the Pretoria National Herbarium (PRE) of the South African National Biodiversity Institute and the Larry Leach Herbarium (UNIN) of the University of Limpopo (UL) for assistance with identification or verification; and as a result, those specimens are lodged with the respective herbaria.The Southern African Plant Invaders Atlas, 2019 (SAPIA) database (Henderson and Wilson 2017) was searched using the name of the area to compare the species list detected.Further categorisation of the species was done following the Alien and Invasive Species Regulations of the National Environmental Management: Biodiversity Act, Act 10 of 2004 (NEM:BA A&IS Regulations) (Department of Environmental Affairs 2014a,b; Moshobane et al. 2019).NEM:BA A&IS Regulations provides four categories of IAS, namely category 1a, 1b, 2 and 3, but see NEM:BA A&IS detailed descriptions.Species and author names are in accordance with the International Plant Names Index (IPNI) and the Integrated Taxonomic Information System (ITIS).

Data analysis
A Kruskal-Wallis test was conducted to determine whether there were differences in the frequency of records of category 1 (1a and 1b) species reported in SAPIA and in the present study.Data were analysed using IBM SPSS version 24, and statistical significance was accepted at p < 0.05.

Results
In Haenertsburg we found 136 taxa belonging to 49 families (106 genera) as represented below (Supplementary material Table S1).Asteraceae was the richest family, with 18 species, followed by Rosaceae (17 spp.), and Fabaceae (12 spp.).These families together comprise 33.8 per cent of the total species.The most diverse genera were Acacia, Ligustrum, and Solanum, with four species each.Genera with single species represented 60.3 per cent of the 136 taxa.Seven taxa were not identified to species level: Bambusoideae, Desmodium, Helichrysum, Rhododendron, Rubus, Sonchus, and Yucca.Four classes were found (30 orders), and the predominant class in the study area was Magnoliopsida with 117 species.
A comparative analysis between the current study and the SAPIA database shows slight similarities but considerable differences in frequencies (Figure 3), 85 in SAPIA 2019 and 51 differences.
We tested for significant differences between the current study and the SAPIA 2019 records (Figure 4).The distributions of scores were similar for all groups, as assessed by visual inspection of a boxplot (Figure 4).Median scores were significantly different between the different surveys (χ 2 = 16.33473,p = .0001).
We found 85 taxa in SAPIA 2019.Among them, only 20 were not found in the current study, and 31 were new to SAPIA from this study.Of the 136 species recorded, 30 are common to both SAPIA and the current study, 48 are unique to SAPIA 219, and 30 are unique to the current study (Figure 3).The new records were submitted for inclusion in SAPIA database.

Discussion
The frequency of occurrence for category 1a and 1b (hereafter "category 1") in the present study was significantly different from the records contained in the SAPIA database.The observed differences could be explained by the survey and follow-up effort, as alluded to by Kalwij et al. (2014).This is also supported by a study by McLean et al. (2017), who compared previous records from various sources.
The higher plant taxonomic richness recorded in this study, which presented a number of known invader species such as Cortaderia selloana, Acacia mearnsii, Eucalyptus spp., and Pinus spp, could indicate the vulnerability of WGG.Based on these findings, it is possible that most documented plants in WGG may have originated from anthropogenic activities such as gardens.As found by McLean et al. (2018), gardens are sources of alien plants in the wild.This was also reported in other studies done in South Africa (Lubbe et al. 2011) and other parts of the world (Smith et al. 2006;Bigirimana et al. 2012).This could be attributed to human activities such as horticultural trades (Marco et al. 2008;Botham et al. 2009;Ööpik et al. 2013).In order to curb the influx and spread, it is necessary to have measures in place to control trading in IAS (Perrings et al. 2005;Hulme 2009;Keller and Perrings 2011).
The South African NEM:BA A&IS regulations ( 2014) established procedures and standards to prevent and control biological invasions.Under this law, the cultivation of some species such as Acacia longifolia, Lonicera japonica, Pittosporum undulatum, and Ulex europaeus is prohibited, while possessing and breeding species such as Acacia mearnsii, Leucaena leucocephala, Morus nigra, and Syzygium cumini is only permitted through the granting of a permit.Another requirement of this regulation is that 1a species such as Morus nigra and Syzygium cumini should be eradicated (Moshobane et al. 2019).Lastly, the regulations list the species that are prohibited for importation into the country (Moshobane et al. 2019).However, the high detection of regulated species in WGG could suggest that species are in fact brought in, whether illegally (Signorile et al. 2016) or legally (Moshobane et al. 2020b).
In the study region, the practice of roadside cutting and burning to create fire breaks is very common (personal observation).This practice benefits Cenchrus clandestinus (Hochst.ex Chiov.)Morrone (previously known as Pennisetum clandestinum Hochst.ex Chiov), since it accelerates the process of invasion, while the native grass species takes time to recover after a fire (D' Antonio and Vitousek 1992;Daehler and Carino 1998).This is because the species sprouts with multiple stems, maximising its occupation of the area and forming dense stands.The present findings indicate the important role of scientific, evidence-based management actions, and they also call into question the use of fire in suppressing IAS.It is suggested, therefore, that active restoration with native species should be encouraged to improve the natural environment and to avoid potential future biological invasions.Forestation with alien trees can also work as a source of propagules for biological invasions (Dehnen-Schmutz et al. 2007).
The occurrence of Pinus patula in WGG is consistent with a number of studies that concluded that Pinus species are aggressive invaders in grasslands around the world (Richardson et al. 2007;Steers et al. 2013;Maitre et al. 2015;Wilgen et al. 2015;Ziller et al. 2019).The main factor responsible for Pinus and Eucalyptus invasions is anthropogenic activities such as forestry.Some of the invasive plants are introduced intentionally around the world for anthropogenic use, and the fact is that half of the species introduced for ornamental purposes have became invasive over time (Hulme 2009b;Morais et al. 2017).Several studies have recommended the incorporation of horticulture and related industries in research, and it is necessary to manage invasive species through the promotion of the greater use of native flora for ornamentals, fruits, and wood (Reichard and White 2001;Cowie et al. 2008;Van Kleunen et al. 2018).
Our findings indicate that shrubs are invading taxa in WGG.The current findings also challenge some of the commonly held beliefs about the fact that predominant invaders are trees (Henderson 1992;Farrar 2001;Gil et al. 2013;Dai et al. 2018): Visser et al. (2017) showed that some grasses are also invasive, and a few selected species do have major impacts around the world, including in South Africa, as reported by Nkuna et al. (2018).Similarly, where woody species invade, they have massive impacts (Ghersa et al. 2002;Richardson and Rejmánek 2011;Dyderski and Jagodziński 2019).Furthermore, the diversity and impact of species is directly related to how long they have been in an area; sometimes the naturalised species present with a long-term pattern of pre-infestation before there is an explosive invasion (Rouget et al. 2016).The following species are not currently spreading in the studied sites: Acacia longifolia, Leucaena leucocephala, Melia azedarach, Ligustrum japonicum, and Eriobotrya japonica.For this group of plants, monitoring is necessary against the possibility of biological invasion in the future.
The discovery of early detection target species such as Coreopsis lanceolata L., Cytisus scoparius (L.) Link, Iris pseudacorus L., and Pueraria montana (Lour.)Merr.indicates that immediate action should be taken to eradicate the populations.It must be emphasised that the economic cost of controlling alien invaders is growing with the passage of time.Because of this, taking precautions is the most efficient strategy to face and prevent biological invasions (Ziller et al. 2007).Taking precautions leads to lower economic costs, and the chance of solving the problems is greater when compared with control strategies after biological invasion has already become established (Blaalid et al. 2021).Thus population of invasive species should be maintained at manageable levels, as detailed in Booy et al. (2017), Bacher et al. (2018), andRoy et al. (2019).
Currently it is necessary to seek strategies to manage invasive species in ecosystems in order to eradicate or even reduce the infestation and control the geographic expansion of these species.The use of invasive alien species in urban and rural afforestation and in degraded areas' recovery projects is not recommended.Other studies are needed to evaluate the alien species of the herbaceous stratum to identify possible biological invaders.

Conclusions
The present study has described a concerning situation.More specifically, this study has provided insights into the baseline data of invasion from alien plant species in the critically endangered WGG.The findings indicate that WGG is facing threat from IAPs, and Furthermore, this points to the important role that is played by early detection research into IAPs.Equally important, there is an urgent need for research and surveillance.There is a particular need to fill the sampling gaps and to understand the various dynamics at play in invasion by plant species.Additional work should attempt to quantify the impacts of the invasions by alien plants -particularly on the natural environment and on ecosystem services according to recognised frameworks, such as that of Blackburn et al. (2011), in order to set management priorities and implement prevention and control strategies that are evidence-based.The outcomes of this study will help to support biodiversity managers and private persons to develop plans and strategies to manage the scourge of biological invasions.It is worth noting that these studies ignored the socio-economic aspect of invasion -a factor that may have influenced the sampling effort and, consequently, the documented richness of the different areas, in addition to differences in geographic size and preservation status between the areas.

Leadership
The Department of Economic Development Environment and Tourism (LEDET), through the Department of Forestry, Fisheries and Environment (DFFE), should establish the Limpopo Invasive Species Forum (LISF).The role of LISF would be to aid in the development of management plans to ensure compliance with the NEM:BA regulations, and to coordinate cooperation between the organs of state, private companies, and private landowners on compliance with the NEM:BA IAS regulations.

Nursery compliance
Although the current study was not able to answer the question about whether local nurseries sell NEMBA-regulated species, previous studies have shown that nurseries do hold restricted plants (Cronin et al. 2017).Therefore it is strongly recommended that the DFFE's compliance directorate develop a nursery compliance strategy, and that a survey be conducted.Lastly, the LEDET should map the location of nurseries in the province and compile a list of the plants traded in all those nurseries.

Public engagement
It was shown that societal perceptions of the impacts of IAS determine people's willingness to act (Estévez et al. 2015); therefore, in order to avoid or manage perceived and potential conflicts (Zengeya et al. 2017), it is recommended that the LEDET, DFFE, local government, and academic institutions conduct stakeholder engagement and participation in management actions for IAS in the area (Shackleton et al. 2019).

Research
Research remains the cornerstone of the effective management of invasive species (Buckley 2008).Therefore it is recommended, first, that the affected parties establish a regional IAS research fund; second, that they establish an IAS research think tank, with SANBI's provincial DBE branch coordinating the research (Wilson et al. 2013); and third, that the research lead to a regional list of IAS (Randall et al. 2008).

Monitoring and eradication
Monitoring was shown to be effective in detecting inconspicuous species (Kalwij et al. 2014).Monitoring should be coupled with a surveillance plan (Hauser and McCarthy 2009) that is fit for purpose in a South African local government setting (Yemshanov et al. 2017).In the event of budgetary constraints, passive surveillance could be developed (Hester and Cacho 2017).SANBI's Directorate on Biodiversity Evidence (DBE), should develop and coordinate an early detection network.This approach has been shown to be useful (Dickinson et al. 2010;Crall et al. 2012).This can be modelled after other successful global programmes (see Anderson et al. 2017;Sarat et al. 2017;Thomas et al. 2017; Varray and Hudin 2017 for more details).LEDET should also fund other monitoring and surveillance efforts such as the use or development of the latest monitoring technologies (Martinez et al. 2020).DFFE should facilitate the early detection of and rapid response to (EDRR) invasive species, and eradicate the NEM:BA category 1a species through its funding of SANBI's DBE (Wilson et al. 2013) and category 1b through the Working for Water (WfW) programme.And DFFE, through the legal directorate, should also delineate the legal authorities, regulations, and policies that would either enable or inhabit EDRR (see Burgos-Rodríguez and Burgiel 2020;Reaser et al. 2020).

Figure 1 .
Figure 1.Shows location of the study area and the the protected area within the Woodbush Granite Grassland (WGG) within the Limpopo province.Green highlighted area = Haenetsburg nature reserve.

Figure 3 .
Figure 3.Comparison of the SAPIA 2019 records and the present study (CURRENT = present study; NEWS = species from the current study that are not contained in the SAPIA; NOTCUR = species that are contained in SAPIA but not in the current study).

Figure 4 .
Figure 4. Box-plot showing the frequencies of category 1 species recorded in the current study and in the SAPIA database.