Carla Petersen 212506197
16 August 2018
Assignment on Field Observations of Alien Plant Invasion on Westville Campus
Indigenous Plant Species
Erythrina caffra, commonly known as ‘Coast Coral Tree’ or ‘Kuskoraalboom’ is an indigenous tree to South Africa and is widely loved for its warm red to scarlet-coloured flowers, which appear from the cold winter months through to spring (Voigt, 2006). Its popularity can be ascribed to its ease of cultivation and long flowering period. The coast coral tree is an ideal garden plant and, because of its unique appearance, it has continued to attract the attention of botanists, horticulturists, nature lovers, and the general gardening public for many decades (Voight, 2006). Erythrina caffra (E. caffra) occurs in coastal sheltered forests and along wooded rivers (Voigt, 2006). It recruits very quickly from seeds, which birds carry across large distances. Although an important and well-used tree in rural areas, the coast coral tree is not endangered. Its ease of cultivation makes it readily available for garden use throughout the country. Both birds and flying insects pollinate coast coral trees (Voigt, 2006). The flowers of E. caffra do not produce any fragrance, so it is only their colour, in combination with the reward of nectar which is produced in abundance, which attracts pollinators. The flowers appear before the leaves, and this may well be a strategy for visible advertising to attract as many nectar-feeding birds as possible. The shape and design of each flower are such that the stamens are exposed, resulting in easy pollen transfer by birds and insects. Moreover, the branches are armed with prickles, which might serve as protection to herbivores especially when trees are still young (Voigt, 2006). Fully grown trees are fairly drought-resistant and can withstand several degrees of frost. In areas where there is severe frost, it may well grow but flowering is unlikely.
In South Africa, E. caffra is seen as a royal tree – it is a much respected and admired tree in the Zulu culture and is believed to have magic properties (Voigt, 2006). Specimens have been planted on the graves of many Zulu chiefs. In parts of the Eastern Cape, local inhabitants will not burn the wood of E. caffra for fear of attracting lightning (Illgner, 2014). Coast coral trees were also planted as living palisades around the houses of the early settlers, and used as fences around kraals and waterholes (Voigt, 2006). In the Peddie District of the Eastern Cape there are a number of these living fences that have been closely planted around waterholes to keep livestock from the water or to channel them to the entrance. The wood is very soft, spongy and light (Voigt, 2006). Hollowed trunks were used to make canoes and troughs, and cubes of wood were used as floats for fishnets. When tarred, the wood made good roofing shingles. The African women of South Africa make the highly decorative seeds of E. caffra into necklaces (Voigt, 2006). Children also love collecting them where they are known as lucky beans. All coast coral trees produce a poison with a curare-like and paralysing action, which is used medicinally to relax the muscles in treating nervous diseases (Voight, 2006). The seeds of all erythrinas are said to be poisonous, and the leaves of E. caffra are known to have poisoned cattle. The bark of the tree is used typically to treat sores, wounds, abscesses and arthritis (Illgner, 2014). Open wounds may be treated with powdered, burnt bark; infusions of the leaves are used as eardrops for earache; and decoctions of the roots are used for sprains. The Vhavenda use the bark for toothache. Erythrina alkaloids are known to be highly toxic, but the traditional uses strongly suggest antibacterial, anti-inflammatory and analgesic effects (Voigt, 2006). More common are the uses as a garden plant (Panga, 2014). These trees are admirably suited for park planting or to line streets of cities, small towns and villages. On lawns they make beautiful specimens as single subjects, but one must be aware that in time these trees may become rather big and larger gardens would therefore be more suitable (Panga, 2014).
Strelitzia nicolai (S. nicolai) is also an indigenous tree toSouth Africa, and its common name is the ‘Natal Wild Banana’. It is an evergreen tree with multi-stems that form dense clumps (Letsela, 2002). It grows mostly in coastal dune vegetation and in evergreen forests near the coast. It is a common feature of the coastal vegetation from East London northwards. It grows in the Eastern Cape, KwaZulu-Natal and up into Mozambique towards Zimbabwe. S. nicolai grows both in the open and in shade (Van Jaarsveld, 1998). This type of plant develops larger leaves when the light intensity is low to expose more ‘green’ surface to the light for photosynthesis and in stronger light the leaves become smaller (Veld and Flora, 1998). Plant leaves act like sun panels: they have to manufacture enough food to provide the plant with energy and, when the sunlight is reduced, they try to compensate by enlarging the leaf surface. Furthermore, the Natal Wild Banana is very hardy and can tolerate a wide range of conditions but not frost (Van Jaarsveld, 1998). Their fleshy roots enable them to withstand dry conditions. Therefore, they may have the potential to become invasive in non-native parts of the world under favourable weather conditions. In Florida, USA, S. nicolai (also known as ‘Giant Bird of Paradise’ or ‘White Bird of Paradise’) are non-native species that have not yet been assessed by horticulture specialists for invasive potential by the Institute of Food and Agricultural Services (IFAS) Invasive Plant Working Group (Wichman et al., 2006). Nonetheless, it does play a significant role for some species. The tree’s purple/blue and cream flowers open in Spring/Summer and attract birds, e.g Sunbirds, and the leaves are used for hibernation by Tree frogs as well as roosting by Banana bats (Grow Wild, 2018).
S. nicolai can be planted as a specimen plant or used for informal hedging/screening (Grow Wild, 2018). Some may find the Natal Wild Banana to become a pest in gardens. For gardening at leisure, it is advised not to plant S. nicolai near drains, walls, paving, swimming pool walls and house foundations due to its fleshy roots which grow rapidly into a huge root ball and exerting tremendous pressure on these platforms (Townsend, 2015). Leaf stalks are dried and used to make a rope for building fish kraals and huts (Letsela, 2002). The immature seeds are edible and tasty. Also, seeds are ground into flour and made into patties which are roasted (Grow Wild, 2018).
The genus Dracaena has approximately 116 species, of which some 63 occur in Africa (including Madagascar) (Damen et al., 2018). The remainder is found in Asia, Australia and Central America. Dracaena aletriformis (D. aletriformis) commonly known as ‘Large-leaved Dragon Tree’ is a shrub or small tree usually with a main stem topped by a rosette of elongate (usually 60-100 cm long) leaves (Robertson, undated). It grows in the shady understorey of forests in South Africa and Swaziland, with its distribution extending from the Eastern Cape to Limpopo, but is most common in the coastal and dune forests of KwaZulu-Natal. Moreover, the Large-leaved Dragon Tree is not fussy about soil and is very drought tolerant. The flowers open from late afternoon to early morning and attract night-active pollinator moths (Viljoen, 2003). Birds eat the fruit which help to remove the orange pulp which contains a growth inhibitor that otherwise slows germination of the seeds.
Various species of Dracaena have a high importance in horticulture, while others show medicinal or social functions in marking graves, sacred sites and farm plots in many African societies (Damen et al., 2008). Globally, Dracaena is in the top ten of most important crops in floriculture, while in the Netherlands Dracaena is in the top five of the most exported pot plants with an annual turnover of an estimated 33 million euro. D. aletriformis are scarce, heavily traded or with a high price in South Africa (Mwachala, 2005). In the Eastern Cape, South Africa, D. aletriformis is used in popular herbal remedies whereby herbs were burnt to smoke out evil spirits or used as a steam for good luck (Cocks and Moller, 2002 and Robertson, undated).
Invasive species
Litsea glutinosa i.e. ‘Indian Laurel’ is an evergreen or deciduous tree belonging to the family Lauraceae, growing approximately six to ten meters high (Mohammad et al., 2016; Patrick, 2016). This large tree can sometimes be confused with the avocado pear, however the crushed leaf will give it away as it has a rather unpleasant smell (Patrick, 2016). The growth form is also similar to an avocado tree. Nonetheless, its yellow-orange flowers which appear in summer from October to May are a giveaway. Litsea glutinosa (L. glutinosa) bear fruit/seeds as pea-sized shiny black berries seated on a disc with one seed inside (Patrick, 2016). The Indian Laurel is native to the Himalayas and south-east Asia and has been introduced and established across the world, including KwaZulu-Natal (especially around Durban) (Invasive Species South Africa, 2018). It grows at an altitude of 500-1900 meters above sea level, in forest margins, stream sides, sparse forests or thickets, as well as regions where rainfall exceeds 1200 mm per year (Heuzé et al., 2015). Furthermore, it colonizes all open areas but also survives in more shaded areas (Vos, 2004). It is also found in undisturbed forest (Heuzé et al., 2015). In India, this tree is very important from economical, medicinal and conservation point of view (Mohammad et al., 2016). L. glutinosa has many ethnomedicinal uses in treating diarrhoea, dysentery, rheumatism and has antispasmodic, wound healing properties (Prusti, 2008). In the Northern Philippines, the leaves are chopped and soaked in water to make plaster (Heuzé et al., 2015). While L. glutinosa gives a poor timber due to its low wood density, it is often used as fuel. It was introduced as a source of fuelwood, in the Comoros archipelago in the mid-19th century, to meet the high demand of the sugarcane distilleries, and later of the cinnamon, ylang-ylang and citronella distilleries (Heuzé et al., 2015). In China, the oil contained in the seed (50%) is used to make soap. More recently, L. glutinosa has been investigated as a source of essential oils, arabinoxylans and other components with antiseptic properties (Heuzé et al., 2015).
Biological invasions are a major threat to biodiversity in most parts of the world (Dlamini et al., 2018). The success of invasive fleshy fruiting plants is linked to the role of native avian frugivores. By ingesting and excreting/regurgitating viable seeds, avian frugivores are able to promote germination and disperse the seeds of these invasive fleshy fruiting plants. A study by Dlamini et al., (2018) examined the effect of native birds Cape white-eyes (Zosterops virens), red-winged starlings (Onychognathus morio), speckled mousebirds (Colius striatus) and dark-capped bulbuls (Pycnonotus tricolor) on germination and dispersal of L. glutinosa seeds by comparing them to those of whole and manually de-pulped L. glutinosa fruit. By comparing the seed retention times and fruit consumed by the various avian species, this study examined which avian species were likely to have the most effect on germination and dispersal of L. glutinosa. Most of the avian species consumed L. glutinosa fruit, with speckled mousebirds being the only exception. However, ingestion of L. glutinosa fruit had no positive effect on germination as none of the seeds germinated (including the control seeds) (Dlamini et al., 2018). Variances in body mass and bill size could potentially mean that larger birds play a greater role in seed dispersal as they ingested a greater number of seeds. Further studies need to be conducted on L. glutinosa in order to determine the conditions in which it germinates in the field and how these may be replicated for germination experiments in the laboratory (Dlamini et al., 2018).
There are very few quantitative data on the degree of invasion of habitats except for the very interesting report by Pascal (1997) for Mayotte which covers, unfortunately, only the humid forests (Vos, 2004). There are some qualitative studies or studies on the ecology of a specific invasive species such as Lantana camara (Mas 1999) and L. glutinosa (Jacq 2001), and on the ecology of weed species (often exotic) in agricultural areas (Vandamme 2001). However, these studies deal only with Mayotte (Vos, 2004). Intermediate-altitude humid forest can be found at various altitudes depending on the exposure of the area, starting at 200 meters above sea level, e.g. Sohoa forest in Mayotte (Vos, 2004). Rainfall is between 1 700 and 2 200 mm per year with between five and seven humid months. L. glutinosa can be found throughout this type of forest. It is also found in undisturbed forest, especially in Mayotte where undisturbed forests are located at lower altitude and where the pressure on this species is decreasing as agriculture declines. L. glutinosa has various successful methods of multiplication and spread, including effective dissemination by frugivores, efficient vegetative multiplication, and a large and long-lasting seed bank (Vos, 2004). In addition, its juvenile period is short, its fruiting period is long and frequent, and its growth is fast. Dormancy of L. glutinosa seeds is not influenced by light (Vos, 2004). Seeds can germinate under leaf litter and the plants even grow in thickets such as those formed by Lantana camara in Mayotte. However, L. glutinosa favours high light regimes and establishes best in open areas. Therefore, the potential for L. glutinosa to invade is high, and competes with indigenous plants causing transformation in habitats (Invasive Species South Africa, 2018). In addition, the environmental status of L. glutinosa differs between countries (Heuzé et al., 2015). In the Northern Philippines, it is considered as a disappearing useful multipurpose tree and is subject to a conservation program. Globally, L. glutinosa is not considered as invasive; however, it has a high invasion potential and displaces regenerating native plant species in disturbed environments. It is considered as opportunistic in the eastern coastal region of China, and invasive in KwaZulu-Natal and several islands of the Indian Ocean (Mauritius, Réunion, Mayotte), though not in the Seychelles. The invasive properties of L. glutinosa can also be used for reforestation of damaged soils (Heuzé et al., 2015). Its invasive status in South Africa is CARA Category 1; NEMBA Category 1b (Invasive Species South Africa, 2018) and must therefore be removed (Patrick, 2016). It is better to remove these when they are still small as the cost to remove a fully grown specimen will be considerable (Patrick, 2016).
Nerium oleander (‘Oleander’), a native plant of the Mediterranean region of southern Europe, is a well-known cultivated plant in South Africa where it is used for ornament in gardens and as a screen on motorway islands (Henderson, 1992). It is an evergreen shrub or small tree with dark, dull-green leaves that are paler below and have distinctive veins and a prominent midrib (Patrick, 2016). Pink, red or white flowers which are slightly aromatic, appear from September to March. This species was introduced from the Mediterranean as a decorative hedge (Patrick, 2016) however, it started to invade mainly dry parts in South Africa and became lethal towards humans, birds and other animals due to its toxicity. The whole plant is highly toxic and lethal and the sap is a skin irritant. This plant used to be the species that was planted throughout KwaZulu-Natal between carriageways on highways. Oleander was planted by many municipalities as hedges and on road verges where it will now have to be removed. This species also competes with indigenous flora. (Patrick, 2016). Less well known is its invasion of watercourses. It is spreading into many mountain river valleys of the Cedarberg, in the Gamka, Huis and Gouritz River valleys of the Ladismith and Calitzdorp districts, and in the Baviaanskloof River Valley north-west of Humansdorp (Henderson, 1992). It rarely produces fertile seed in the summer rainfall areas and consequently it has not been reported as a problem plant in these areas. In South Africa, as well as in the Mediterranean region, oleander usually grows naturally only along watercourses (Henderson, 1992). It seems to have a preference for gravelly and rocky streambeds. It has been described as a “rheophyte”; i.e. a plant species that is confined to the beds of swift-running streams and rivers where it grows up to flood-level, but not further than the reach of regularly occurring flash floods (Henderson, 1992). Many rheophytes, like oleander, can be easily cultivated away from their rheophytic habitat. Young oleander seedlings are extremely sensitive to drought and need a steady supply of soil moisture.
Oleander should be regarded as an extremely undesirable garden plant due to its extreme toxicity (Henderson, 1992). In South Africa, it is regarded as a Category 1b plant whereby widespread invasives require compulsory control and ideally be removed from properties (Invasive Species South Africa, 2018). N. oleander survives drought well and is well-suited to growing on soil too poor for most other shrubs, even tolerating salt spray, brackish water, and alkaline soil (Gilman and Watson, 1994). It thrives in full sun, appearing too lanky and flowering little if planted in partial shade. Moreover, it grows following wet weather, slowing down in drought, but always looks good even in powder-dry soil. Oleander invades fresh water perennial and seasonal river beds on the inland mountain slopes (Milton, undated). There are dense invasions of this species in the Hantamsrivier within the Karoo Central Astronomy Advantage Area east of Calvinia but it is absent in saline or alkaline rivers in the Karoo Central Astronomy Advantage Area. The seeds are attached to silky parachutes and drift on wind and water (Milton, undated). However its deep roots and vigorous sprouting ability is what makes this invasive Asian plant difficult to control. N. oleander provides little or no reward for food-seeking animals such as insects and birds. In a study of two wild oleander populations in southern Spain by J. Herrera it was discovered that the showy flowers are nectarless, providing little pollen, and depending on “false advertising” for pollination (Henderson, 1992). Despite the fact that oleander is rarely visited by pollinators it depends on them for reproduction. Automatic pollination does not occur because the pollen bearing anthers and the receptive stigmatic surface are separated. However, Oleander is still successful in pollination and seed-set to occur. Herrera (1991) points to two key points for its successful pollination in the Mediterranean region (and the same is likely to apply in the southern Cape with its Mediterranean-type climate). These are its ability to flower during the hot summer months when few other plants are in bloom, and the high diversity and activity of bees at this time (Henderson, 1999). Successful seed-set is accomplished by the fertilization of large numbers of ovules (300 – 400 per ovary) in a single, probably rare, pollination event. The small feathery seeds are adapted for wind and water dispersal and are unlikely to have any food value to animals. Although it has little invasive, if any, invasive potential (Gilman and Watson, 1994) management of this species should be upheld to prevent the loss of biodiversity. Furthermore, it was recently declared a Category 1b species in South Africa, thus increasing its potential of invading land.
Syzygium cumini (S. cumini), also commonly known as Jambolan, is a large evergreen multipurpose tree of family Myrtaceae (Khan and Sharma, 2010). It reaches a height of up to 15 to 30 meters. The Jambolan tree which is native to India thrives easily in tropical climate under a variety of environmental conditions and is found in many parts of Asia and Eastern Africa (Global Invasive Species Database, 2018; Khan and Sharma, 2010). Jambolan can thrive in a variety of soils in low, wet areas and on higher, well-drained land (loam, marl, sandy soils, calcareous soils) (Global Invasive Species Database, 2018). It grows well in areas receiving heavy rainfall between 1 500 – 10 000 mm per annum. It develops most luxuriantly in regions of heavy rainfall, as 1 000 cm annually. It is sensitive to frost when young but mature trees have been undamaged by brief below-freezing temperatures in southern Florida (Global Invasive Species Database, 2018). S. cumini is one of the most widely used medicinal plants in the treatment of various diseases in particular diabetes (Ayyanar and Subash-Babu, 2012). Jambolan fruit can be eaten raw and can be made into tarts, sauces and jams (CABI, 2018). Also, Jambolans are an important source of wine, somewhat like Port, in Goa and the Philippines. Therefore, this multipurpose tree has a high economic value, providing a good enough reason to be cultivated.
S. cumini has been introduced to many different places where it has been utilised as a fruit producer, as an ornamental and also for its timber (Global Invasive Species Database, 2018). It is thought to have been spread intentionally during pre-history to Bhutan, Nepal, China, Malaysia, the Philippines, Java and elsewhere in the East Indies, and to Queensland and New South Wales, also on the islands of Zanzibar and Pemba (Tanzania) and Mombasa and the adjacent coast of Kenya (CABI, 2018). S. cumini is a fast-growing tropical and sub-tropical tree preferring moist, riverine habitats (CABI, 2018).It grows rapidly, coppices, and tends to form monocultures which shade out native vegetation. It has the ability to form a dense cover, excluding all other species (CABI, 2018). This characteristic has allowed S. cumini to become invasive in Hawaii where it prevents the re-establishment of native lowland forest and very invasive in the Cook Islands and in French Polynesia (Global Invasive Species Database, 2018). It invades coastal bush and savanna in South Africa (CABI, 2018). Although it is not an aggressive invader of undisturbed forest like the closely related Roseapple (Syzygium jambos) (Global Invasive Species Database, 2018). S. cumini has not been evaluated for biological control, but vigorous efforts to exterminate it with herbicides are taking place in Hawaii. S. cumini is a Category 1 invasive plant in Florida, USA and a Category 3 invasive plant in South Africa, and is invasive in several Pacific islands, especially in the Cook Islands (CABI, 2018). It has naturalised in many other countries where it was introduced and is likely to spread further.
Exotic species
Washingtonia filifera (W. filifera) or the ‘California Fan Palm’ is native to the south-western deserts of the United States, but grows well in South African climate (Mukaro, 2017). It is a popular tree in gardens to create a tropical feel; this palm may be able to handle South Africa’s harsh climate with relative ease (Mukaro, 2017). W. filifera is also often used as an avenue tree in South African cities. California Fan Palm provides shelter and food to many animals such as various rodents use the palm’s shag for cover; a species of rat snake (Elaphe rosalica) depends upon the shag for shelter and food (rodents); and oases attract numerous species of birds because of the relative abundance of food, shelter, and nesting sites (Edwards, undated). .Furthermore, California Fan Palm is widely cultivated and is greatly valued as a landscaping ornamental tree. Kamia and Cahuilla Indians selected California Fan Palm oases for village sites (Edwards, undated). W. filifera vegetative buds, flowers, and fruits were utilized as food. The fruits, resembling commercial dates in taste, were eaten fresh or dried; some dried fruit was made into meal (Edwards, undated). Leaves were used as thatching. Sandals, clothing, and baskets were fashioned from leaf fibres. Spoons and hunting bows were made from the petioles. (Edwards, undated). The wood was used for kindling. Because of historical use by Indians, W. filifera oases are important archaeological sites (Edwards, undated).
The root system is compact and fibrous which means that the palm can be grown successfully in an area where the roots are restricted i.e. in large containers (Mukaro, 2017). Hardy and drought resistant, W. filifera needs full sun exposure and will grow faster with regular watering. It is also wind resistant and will tolerate exposure to frost. California Fan Palm is moderately shade-tolerant when young, becoming intolerant with age (Edwards, undated). California Fan Palm communities require moist pioneer conditions. They are invaded by shrubs in the absence of fire, creating environmental conditions which eventually kill the palms. Therefore, both artificial and natural fires are important factors affecting the growth of W. filifera and the oases (Edwards, undated). Burning increased the yield of fruit crops, removed the dead shag from trunks for easier access to crops, and removed understory phreatophytes competing for water resources. California Fan Palms are fire resistant (Edwards, undated). They are rarely killed by either the initial burning of their shag or by subsequent burnings (Edwards, undated). Burning experiments show that their fibrous trunks are difficult to ignite and almost impossible to flame. Each successive burning kills some outer vascular bundles and burns off some of the trunk, causing a reduction of trunk diameter. Crown fire, a common occurrence, reduces crown size (Edwards, undated). Repeated burnings sometimes results in fire-dwarfed trees. Reduction in trunk and crown reduces the evapotranspiration rate, making more effective use of limited water supplies and allowing for a greater number of palms per oasis. Wind-blown, advancing crown fire does not inflict as much damage or kill as many palms as a slow-moving fire burning in still air (Holden, 1993). W. filifera fruit allelopathically inhibits germination and growth of other species under laboratory conditions (Edwards, undated). Thus their coping mechanisms to adapt to changing environments is advantageous. Furthermore, populations should be monitored as to not outcompete indigenous species.
Ficus religiosa (commonly known as Sacred Fig Tree) is a long-lived valuable multipurpose forest tree (Siwach and Gill, 2011). The tree is exploited because of its religious, ornamental and medicinal value and the regeneration rate in natural habitat is low. It is said to be the tree that Buddha was born under and also where he sat for six years of meditation and enlightenment (Tree et al., 2003). Ficus religiosa (F. religiosa) is native to India and is widely found wild or cultivated throughout India, Pakistan, Bangladesh, Ceylon, China, Burma and Thailand (Siwach and Gill, 2011). The tree attains large dimensions and has long life span. It is heavily branched with long petiolated, long tipped, leathery, heart-shaped leaves and is very popular as a shade tree. This large tree with attractive heart shaped glossy leaves is occasionally planted as a specimen tree in landscaping for its aesthetic shape and form (Tree et al., 2003). It is also commonly planted as an avenue or roadside tree and most frequently near temples (Siwach and Gill, 2011).
F. religiosa has been intentionally introduced around the world for use as an ornamental, and accidentally imported beyond its native range through horticulture to places including Israel and Hawaii (Datiles and Acevedo-Rodriguez, 2014). Furthermore, it is widely cultivated in the tropics and subtropics, including South Africa (Van Noort and Rasplus, 2018). Its ability to naturalize in introduced settings depends on whether its species-specialist pollinator wasp has also been introduced to the region; so far the species has only been reported to set viable seed in Florida, Israel, and, most recently, Maui Island of Hawaii (Datiles and Acevedo-Rodriguez, 2014). As it can reproduce by both seeds and cuttings, the species might be dispersed by birds that feed on the fruit, or by cattle and other foragers that eat its leaves and twigs (Datiles and Acevedo-Rodriguez, 2014). The Sacred Fig Tree has been listed as an “environmental weed” or “naturalised weed” by the Global Compendium of Weeds (Datiles and Acevedo-Rodriguez, 2014). It has been assigned an invasiveness high risk score of 7 in a risk assessment prepared for the species’ invasiveness in Hawaii by PIER, such a high score predicts it will become a major pest in suitable climate zones. The major reasons for its invasive behaviour are its fast-growing nature, tolerance to various climate zones and soil types, reported lifespan of over 3,000 years, and its suffocating growth habit as it often begins life as an epiphyte (Datiles and Acevedo-Rodriguez, 2014). Whilst it can reproduce either through seed production or through cuttings, it does require a species-specific pollinator wasp (Datiles and Acevedo-Rodriguez, 2014). Each member of the Ficus genus has a symbiotic relationship with an agaonid wasp; just as each Ficus species requires a specific wasp in order to pollinate, the wasp will only lay eggs within its associated Ficus species (Datiles and Acevedo-Rodriguez, 2014). F. religiosa is associated with the wasp Blastophaga quadraticeps, which is now known to be present in a limited number of introduced places – Hawaii, Florida, and Israel (Datiles and Acevedo-Rodriguez, 2014).
In South Africa, its pollinator is the wasp Platyscapa quadraticeps Mayr (van Noort and Rasplus, 2018). Fig Trees are common subjects in the horticultural trade and a number of species have been distributed by man around the world (van Noort et al., 2013). There are 15 or more species of exotic fig trees present in Africa, of which at least eight are being commonly propagated. Fig trees depend on host specific fig wasps (Agaonidae) for pollination, and consequently cannot reproduce sexually in the absence of their associated pollinator species. Most of the exotic fig tree species grown in southern Africa and elsewhere have none of their associated fig wasps present, and consequently cannot reproduce. Among the exceptions includes the Indian F. religiosa (van Noort et al., 2013). F. religiosa has its pollinator present in southern Africa and is reproducing successfully, although not spreading. Furthermore, the Scared Fig Tree is highly unlikely to establish in most of southern Africa, because of the contrast in conditions compared with the monsoonal climate of its natural distribution, but in higher rainfall areas F. religiosa may be able to colonise areas of natural vegetation. The pollinator has been established in Africa for at least 22 years and to date there is no indication that the host fig is problematic by colonizing new areas (Van Noort et al., 2013). Considering these characteristics and its known potential for invasiveness, but also its dependence on a specialist pollinator, the risk of introduction for this species is high in places where its specialist pollinator wasp is present. Preventing the pollinator wasp from entering non-native places is of utmost priority to prevent F. religiosa from becoming naturalized and potentially invasive to non-native places (Datiles and Acevedo-Rodriguez, 2014).
Cotoneaster pannosus, commonly known as ‘Silver Leaf Cotoneaster’, is an exotic shrub in South Africa, growing up to three meters high with arching branches and showy, berry-like fruits (Invasive Species South Africa, 2018). It originally comes from China and naturalised elsewhere, for example Zimbabwe and South Africa (Hyde et al., 2018. Moreover, the shrub seems to be problematic in the Free State province (Invasive Species South Africa, 2018). Cotoneaster pannosus (C. pannosus) invasive status in South Africa falls under CARA 2002 – Category 3 and NEMBA – Category 1b (Invasive Species South Africa, 2018) which states that further planting, propagation or trade, is however prohibited and invasive species which must be controlled and where possible, removed and destroyed. (Moreroa, 2014). Furthermore, any form or trade or planting is strictly prohibited (DEA, undated). The Silver Leaf Cotoneaster is cultivated for hedging and is also used as an ornamental (Invasive Species South Africa, 2018).
C. pannosus competes with and has the potential to replace indigenous species (Invasive Species South Africa, 2018). Dense stands could reduce grazing available for domestic and wild animals. Each biome has a different suite of prominent invaders (Henderson, 2007). In part, this can be explained by their pre-adaption to the prevailing environmental conditions, but also to their history of planting. Although widely planted, in South Africa C. pannosus have become prominent invaders in only one biome (grasslands), indicating that environmental factors have limited their distribution (Henderson, 2007). This shrub is virtually restricted to high-altitude grasslands where it appears that freezing winter temperatures are needed to trigger seed germination (Henderson, 2007).
References:
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Cocks, M. and Møller, V., 2002. Use of indigenous and indigenised medicines to enhance personal well-being: a South African case study. Social science & medicine, 54(3), pp.387-397.
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Dlamini, P., Zachariades, C. and Downs, C.T., 2018. The effect of frugivorous birds on seed dispersal and germination of the invasive Brazilian pepper tree (Schinus terebinthifolius) and Indian laurel (Litsea glutinosa). South African Journal of Botany, 114, pp.61-68.
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