C. camphora is a designated noxious weed in north-eastern New South Wales and an important weed in south-east Queensland, Australia). It dominates the landscape in cleared or disturbed hillsides, valleys and watercourses approximately 100 years after...
C. camphora is a designated noxious weed in north-eastern New South Wales and an important weed in south-east Queensland, Australia). It dominates the landscape in cleared or disturbed hillsides, valleys and watercourses approximately 100 years after it was extensively planted as an ornamental tree species, particularly on elevated krasnozem soils. C. camphora bears heavy fruit loads which are attractive to a number of bird species, which spread seed extensively, and seed have excellent viability in the first year. It forms single-dominant stands that dominates other vegetation and is a major economic weed pest to landholders, power authorities and local councils. It is spreading in other agricultural areas on the east coast of Australia, and there is potential for spread in other sub-tropical areas throughout the world.
The genus Cinnamomum (family Lauraceae) contains about 350 species indigenous to the Asia-Pacific Region and tropical America. Considerable taxonomic confusion regarding C. camphora has occurred in the past; see recent treatments in Wu (1979) and Li (1982).
C. camphora in open habitats is a large evergreen tree with a stout, uniformly cylindrical bole and dense, symmetrical crown. In its native habitat it attains a height of 20-30 m with wide spreading branches and a trunk 50-100 cm in diameter (Dewey, 1897), although in China it can reach up to 50 m tall with a dbh of 300 cm. In India and Nepal the dbh ranges from 50 to 300 cm, and in subtropical eastern Australia up to 200 cm. When young,the bark is green and smooth, later it turns yellow-brown or grey-brown with vertical splitting. The root system is dominant in the top 50 cm of soil (Ji et al., 1998) and, heavily branched with extensive lateral roots (Firth, 1979).
The foliar and floral description is based on observations of naturalized trees of the predominantly camphor oil form in subtropical Australia (Firth, 1979). The leaves are simple, petiolate, alternate, usually broadly lanceolate to ovate-elliptic, acuminate at base and apex; light green with smooth and shining upper surface and whitish or glaucous on the under surface. Leaf size varies from a maximum of approximately 10 x 5 cm to an average size of 6-7 x 3 cm (exclusive of petiole). Petioles are pale green and 2-4 cm long. Young leaves pinkish in colour for 2-3 weeks after leaving the bud, with a soft and soapy texture when touched, characteristic of new foliage on young trees in spring. Leaf venation is characterized by a lower pair of lateral veins more prominent than the other, but leaves are not distinctly 3-nerved as those of the cinnamon and many other species of the genus. Impressed glands (domatia) appear in the axils of the lower two pairs of main veins, being most pronounced in one cineole-rich variant of the species. Leaves thicken with age to maturity, although remaining fairly thin and flexible for a mesophytic species. Leaf colour varies with environment, season, and age of the tree, younger trees having darker green leaves where environment is suitable.
Buds are scaly, usually pinkish in colour in late winter, similar to the leaves that emerge from them, and burst in the spring into new leaves and inflorescences, usually associated with the fall of old leaves. Inflorescences are white, axillary, paniculate, glabrous, pedunculate, shorter than leaves, bracts caducous, and composed of numerous tiny florets. Flowers are bisexual, membranous, linear, soft-pubescent. The perianth is membranaceus, segments 1.5 mm long, yellow-green and elliptic. The globular fruit is 7-8 mm wide and purplish-black and develops to maturity in late summer-autumn as a berry-like one seeded drupe (Zheng, 1978; Storrs and Storrs, 1984; Gupta, 1993). The fruiting pedicels terminate in a saucer-shaped disc, persisting after the fruit has fallen. The seed has a thin, hard testa, brown in colour and darkening with age, and contains hard white cotyledons.
C. camphora is native to warm temperate to subtropical areas of East Asia including China, Vietnam, Korea and Japan, specifically to the coastal areas from Cochin China (Vietnam) to the mouth of the Yang-tse-kiang River and adjacent islands including Taiwan and Hainan, and extends inland 800 km from the mouth of the Yang-tse-kiang. The limits of the native range are approximately 10-36°N and 105-130°E.
The distribution in this summary table is based on all the information available. When several references are cited, they may give conflicting information on the status. Further details may be available for individual references in the Distribution Table Details section which can be selected by going to Generate Report.
C. camphora is extensively cultivated throughout southern China, Taiwan, Korea, Japan and India (Zheng, 1978; Storrs and Storrs, 1984; Gupta, 1993). In the Indian region, plantations have been established in the temperate areas of Nepal, India (northern India, Uttar Pradesh, West Bengal, Tamil Nadu and Karnataka) and Myanmar (Maymyo and southern Shan States). In Indonesia (northern Kalimantan), Mauritius, Tanzania, Kenya and Australia it is (or has been) cultivated as an ornamental species (Zheng, 1978; Firth, 1979; Storrs and Storrs, 1984; Gupta, 1993). In addition, C. camphora has been extensively introduced to other countries, presumably as a garden ornamental species during the colonization of European settlements in the mid 1800s, especially along European trade routes and colonies, including Argentina (Buenos Aires), Egypt, Madagascar, Mauritius, France (south-east), Spain (Canary Islands) and the USA (California and Florida) and is becoming widely naturalized in sub-tropical to warm temperate climates in a number of countries.
In Australia, camphor laurel was introduced from the Royal Botanic Gardens, Kew, UK as seed or cuttings in about 1822, and planted in municipal parks in Brisbane and Sydney in 1850-1860 (Firth, 1980). These became the parent trees for extensive propagation in State Forest nurseries from 1890-1910 for wide distribution along the east coast for planting as an ornamental and shade tree in school yards, municipal parks, on government land, and for shade and shelterbelts on farms in northern New South Wales. The species naturalized extensively from these seed parents in northern New South Wales and south-east Queensland, and to a lesser extent from Nowra south of Sydney (35°S, 151°E) north to Cooktown (16°S, 145°E) in northern Queensland (Firth, 1981). The main period of expansion in northern New South Wales coincided with a decline in intensive land management associated with a decline of the dairy industry and abandonment of hillside banana plantations from 1950. It was first described as a weed in 1979, but not officially designated as a weed under State legislation until the late 1990s (Scott, 1999; Firth and Ensbey 2003).
Further spread of C. camphora into areas which have not yet recorded this species as a weed is likely, owing to deliberate introduction as an ornamental, timber or oil-bearing species, e.g. to the southern USA, South America and South Africa. The species has already been introduced into many countries where the climate could aid its spread as a weed in much the same way as it has in eastern Australia over the past 50 years, where it is now classed as a weed in many areas.
C. camphora inhabits disturbed areas, rocky hillsides, neglected agricultural/horticultural areas, fence lines, stream banks (Sainty et al., 1995), roadsides (Firth, 1980) and railway embankments. Apart from small areas of rainforest remnants there is limited competition from other tree species, apart from privet (Ligustrum spp.), another common introduced weed. It also forms a part of broadleaved evergreen forests, mixed forests and moist forests.
Detailed studies of native Cinnamomum in Taiwan reveal morphologically distinct species and varieties. The type, Cinnamomum camphora var. camphora ('Kusunoki') has three forms based on essential oil composition. (1) The camphor form ('Hon-Sho') is the 'true' camphor tree and the most important form for extraction of camphor, the Taiwanese and Japanese forms being identical, although some botanists classify the Japanese form as var. camphora, and the Taiwanese form var. formosana. (2) The linalool form ('Ho-Sho') known as the fragrant camphor tree, the dominant oil being linalool, though some botanists have classified this var. glaucescens or var. linaloolifera (Fujita, 1950). (3) The cineole form ('Yu-Sho') is the most important physiological form in China though producing little camphor but a high proportion of cineole in its oil.
C. camphora var. nominale ('Rau-Kusu' or 'Kusunoki-Damashi') is a morphologically distinct variety occurring in dry, windy habitats in Taiwan, and is much smaller than other varieties with a height of 3 m and stem diameters of 5-10 cm. Cinnamomum kanahirai ('Sho-Gyu') is another species of 'camphor tree' growing at altitudes of 1000-1700 m in the north of Taiwan and 1600-1800 m in the south, its essential oil containing no camphor, the main constituent being terpinen-4-ol. Cinnamomum micranthum ('Ohba-Kusu' or 'Pha-Chium') is a thrid species, commonly called the large-leaf camphor tree, growing naturally in northern Taiwan below 1000 m, the essential oil contains 95% safrole.
In countries where Camphor laurel is naturalized the camphor form is dominant (70-80%) such as in Cuba (Pino, 1998), Assam, India (Pindey et al., 1997) and France (Pelissier et al., 1995). However, cineole and linalool forms can occur as well as probable hybrids of these, such as the linalool form being dominant in Brazil (Prizzo et al., 2000).
In Queensland, Australia, where C. camphora is invasive (Firth, 1981; Scott, 1999; Bationoff and Butler, 2002), observations and preliminary oil analysis have revealed that C. camphora appears to be the only species present (Firth, 1979), in accordance with recorded information on its introduction (Firth, 1980). However, variation in form within the species is not easily distinguished on morphological features because of the range in tree size, leaf shape and size, and relative vigour in response to different habitats. Smaller, less vigorous trees are found on soils where there is periodic waterlogging, periodic drought, in low rainfall areas, and where soil depth and permeability are sub-optimal. In northern New South Wales, separate forms were initially identified based on bark characteristics of old ornamental trees, although there was some variation in fruit size and flowering time. Leaf oil of representative specimens of the most common form in the region contained 79-82% camphor, a late flowering form contained 58% cineole, and a rough-barked form contained 47% cineole(Firth, 1979). It is probable that hybridization occurs among these forms and there is some evidence for some chemotypes being more toxic to bird life (Phan et al., 1998).
Physiology and Phenology
Development of seedlings in the glasshouse indicated 4 formed leaves and branching of secondary roots after 13 weeks, and a shoot about 25 cm high with numerous large leaves and extensive root system after 6 months. Establishment is relatively slow in the field until the root system is well established at 1-2 years. A lignotuber-like growth at the base of the stem was found on some field-grown trees 2-3 years old. Trees attain a height of approximately 8 m after 7-8 years under optimum growing conditions in the sub-tropics in Australia when they begin to bear fruit. Intensively- and well-managed sites containing pure stands of 12-year-old C. camphora in Guangdong, China, have recorded an average stand height of 8 m (Zhou, 1984). Many trees in their native habitat are harvested when 120 years old and up to 500 years old in Taiwan (Guenther, 1950). In 80 year-old dense closed stands of the species where it is a weed in the Australian subtropics, there is a range of tree sizes and shapes, depending on age, the bole of younger trees being longer, and with reduced diameter.
Spring is the main time for new leaf growth and flowering. In China and India it flowers in April-May, and the fruits ripen in October-November (Zheng, 1978; Miao, 1982; Ohwi, 1984; Gupta, 1993), and in Australia it flowers in September-October and fruits are fully formed in early autumn, ripening in late autumn (April-May).
Propagation is completely by seeds, produced in large numbers of fruits (up to 100,000 in mature trees) which are consumed by a variety of birds, especially pigeons in eastern Australia, and dispersed over their territory during the southern autumn and early winter. Water dispersal also occurs, fruits floating for up to 20 days in water with no effect on germination (Firth, 1979). Seed longevity varies depending on water content and environment but appears to be < 3 years. Viability of seed stored in the laboratory was approximately 13% after 2 years and 0% after 3 years (Firth, 1979). Germination from surface-sown seeds was virtually nil under natural rainfall and 1% remained viable after 12 months (Panetta, 2001) and nil in the laboratory after 8 months when dry (Chien, 1999).
Germination appears to be inhibited while the seed remains in contact with the flesh of ripe fruits, which appear to release inhibitory substances (Firth, 1979; Panetta, 2001). Germination commences at 8-12 weeks in the glasshouse and extends over 22 weeks. Germination in the laboratory was enhanced by removal of the seed coat (Bahuguna et al., 1987). Unwashed seeds of mature, green (unripened) fruits demonstrated earlier germination (17% after 8 weeks compared to 2-7% for seeds of ripe fruits) and more uniform germination in the glasshouse (Firth, 1979). Water immersion and transport does not impair germination, as indicated by soaking of excised seeds and whole fruits for up to 40 days and 20 days, respectively, in water (Firth, 1979). Germination occurs in spring in the field, presumably after winter stratification and dilution of remnants of inhibitory substances in the fruit and seed coat.
The native range of C. camphora is in the Asian eastern monsoon zone characterized by predominantly summer rains and winter temperatures rarely below freezing, but has now become abundantly naturalized in a wide variety of climates throughout the world. In areas where the species has naturalized successfully the climate is subtropical. Being native to the eastern monsoon region, climatic requirements for optimum growth of C. camphora include sub-tropical warm, moist summers and mild winters. These conditions are found in temperate or subtropical regions at altitudes of 50-1000 m and in tropical regions between 1000-2000 m. The best growth occurs with mean annual rainfall greater than 1000 mm and uniform rainfall distribution. The preferred mean annual temperature is above 16°C, but it can survive lower temperatures down to -9°C. Seedlings may suffer slight frost damage in some years (Zheng, 1978; Zhou, 1984; Gupta, 1993). C. camphora is a light-demanding species that readily colonizes exposed fertile soils. As a seedling it survives light shade, but once above 2-3 m tall it requires full overhead light. Site conditions and stand density influence the content of camphor and oil; the highest quantity of camphor has been found in trees growing on sandy loams and the lowest content on clay (Zheng, 1978; Zhou, 1984; Gupta, 1993). In subtropical eastern Australia it can withstand dry spring conditions once established. Although adapted to establish in open ground, it can tolerate some shade and form single-dominant stands which excludes other species for many years.
It grows best on elevated free draining, acid, krasnozem (red ferrosol) soils in a subtropical climate near the coast in eastern Australia (28°S, 153°E) where annual rainfall is 1000-2000 mm and frosts are infrequent. These soils were dominated by rainforest until cleared for agriculture and grazing approx 150 years ago and have low pH and high levels of aluminium and iron oxides (Firth, 1981). It is also found on other soil types and lowland areas, although it is slower growing there (Firth, 1979). It is not found close to the sea nor does it colonize eucalypt forests. C. camphora prefers light/medium sandy loam to sandy clay loam, and freshly drained fertile soils. The pH value ranges from acid to neutral, but the species can tolerate saline soils <0.2%). It does not grow well on heavy-textured and infertile soils with impeded drainage, but does well on moderately heavy soils. It grows well on either flat or sloping sites (Zheng, 1978; Zhou, 1984; Gupta, 1993).
C. camphora is host to a number of species of birds in eastern Australia, and has been credited with rejuvenating declining numbers of some pigeon species. It is also host to the red spider mite, which is a pest of avocados and is a host for the sunblotch virus (viroid) of avocado (Graca and Vuuren, 1981). C. camphora is found in association with other weed species including Lantana camara, Eupatorium adenophorum and E. riparium, Bacccharis halimifolia and Ligustrum spp in the early succession stages in eastern Australia (Firth, 1981). In later succession stages, Acacia melanoxylon and the rainforest species Mallotus philipensis, Pittosporum undulatum and Guioa semiglauca are sometimes found in association. A number of rainforest species occur in the ground stratum of oldest stands of C. camphora (>50 years), but appear to be suppressed until a gap in the canopy occurs (Firth, 1979).
In China, 39 species of pests have been recorded affecting C. camphora. These are predominantly omnivorous Lepidoptera and Coleoptera insects, two species of termites and two Acariformes (Xiao, 1992). Other pests recorded more recently as causing damage in its native environment include Propachys nigrivena (Zhou, 2000), mites (Fan and Zhang, 2002), Atysa cinnamomi beetle (Chen, 1978), sawfly larvae (Mesoneura rufononta) (Wu et al., 1982), Thymiatris sp. larvae, a pest of leaves and stem (Zhao et al., 1985), Cerace stipitana (Zhang, 1998), Frukstorferiola tonkinaris (Huang, 1985), Charaxes bernardus caterpillar (Li et al., 1984), a number of species of scale insects, and leaf bee (Chang et al., 1998) in Taiwan.
Disease organisms causing damage in the native range of C. camphora include Phellinus noxius (brown root disease) (Arin et al., 1999), and Botryosphaeria dothidea canker (Deng and Guo, 1998). Termites have been recorded in introduced trees in Egypt (Eraky, 1999), and the blue triangle butterfly (Firth, 1979) in Australia, and avocado brown mite (Oligonchus punicae) (Kuang, 1983). Plumosa emarginata (Sohi, 1977) and Glomerella cingulate leaf blight (Khanna and Chandra, 1977) have been recorded in India, otherwise there are no recorded pests or diseases where the species has been introduced.
Propagation is by seeds produced in drupes about 5 mm diameter, available in large numbers in autumn, and which are attractive to a number of bird species, ingested with fruits and deposited along fencelines and under other tree species used for roosting. Birds are the main agent of dispersal of seeds, particularly the pied currawong (Strepera graculina) and the white-headed pigeon (Columba leucomela) in eastern Australia (Firth, 1979).
Clearing or removal of extensive stands of the species is expensive. However, C. camphora usually invades land that is not intensively utilized, such as rocky hillsides, abandoned or poorly managed agricultural land, stream banks, etc. (Firth, 1981), but once invasion has occurred and C. camphora is well established, the land is unusable for agriculture or grazing and is expensive to reclaim. Control along fence lines and water courses are an ongoing cost for landholders where C. camphora is a weed problem. Local government councils and electricity authorities incur an ongoing cost to control it along roadsides and under power lines. Also, the species requires control in native rainforest regeneration programmes. The potential returns from timber harvesting are limited in naturalized stands in eastern Australia, but there is potential to use wood pulp as a fuel for generating electricity (Firth and Ensbey, 2003). The species is not a major host to pests and diseases in countries to which it has been introduced. C. camphora does not directly affect other crop plants in Australia. However, as the stands develop and monocultures form, potentially useful land for grazing or other purposes is reduced due to shading and ecological dominance of the area it inhabits for a long period of time.
Apart from intense competition for soil nutrients, there is also some evidence of allelopathy by this species (Firth, 1979). Whereas native tree species regeneration is initially excluded in single-dominant stands, a ground stratum of rainforest species seedlings is evident in stands where camphor seed parent trees are at least 50 years old. C. camphora has a tendency for single-dominance which tends to exclude other tree species and alienate large areas of land if uncontrolled in north-eastern New South Wales, Australia. There is recent evidence that volatiles exuded from leaves, fruits and wood of some chemotypes of the species can poison animal and bird life in and around small ponds and watercourses. However, this has to be balanced against the evidence for increased numbers of some pigeon species given the relative absence of other tree species, and the aesthetic value of C. camphora where other tree species are sparsely present.
The ease of establishment of this invasive tree species in north-eastern New South Wales, Australia poses a constant threat to local government authorities and landholders with respect to the need to control it. However, its attractiveness in a landscape which was for many years largely devoid of other trees enhanced the attractiveness for aesthetic appeal and for tourism. There is also some conflict between some conservationists and timber harvesters and local authorities that have designated it as a weed.
In China, agroforesty (intercropping with agricultural crops) is practiced at the seedling stage, such as the establishment of mixed forests of C. camphora with Acacia confusa, Casuarina equisetifolia and Cunninghamia lanceolata in Guangxi and Fujian, China (Zheng, 1978). In China and elsewhere in Asia, C. camphora is planted as an ornamental tree in gardens or along roadsides (Zhou, 1984; Fu et al., 1996; Su, 2001).
C. camphora wood is heavy, moderately strong and resistant to insect damage and decay. It has a wide range of wood uses and is well known for its use in cases for storing clothes (Zheng, 1978; Zhou, 1984; Gupta, 1993). In India and Nepal it is greatly valued as a fuelwood for cremating corpses. There is potential for it to be established as an important commercial forest tree (Zheng, 1978; Gupta, 1993).
Camphor is used in the pharmaceutical and perfume industry. Camphor also finds uses in the celluloid and electric-insulator industry. C. camphora is also known for its use as a moth deterrent and as aromatherapy oil. The seed oil can be used for making soap and as a lubricant. The leaves are also used as a fodder for the 'silk fishing line' moth (Eriogyna pyretorum). Some 52 compounds have been detected from the essential oils and dichloromethane extracts of the stems, leaves and bark of C. camphora (Pelissier et al., 1995). Although camphor oil can be artificially synthesized, and eucalyptus oil is an alternative, it is still cultivated for its oils in China for use as a mosquito repellant (Ma et al., 2001), to treat opthalmic disorders (Biswas et al., 2001), as a bactericidal oil (Zhang et al., 2000), for control of bollworm (Xin et al., 2000), dust mites (Hiramatsu and Miyasaki 2001), Candida albens and ringworm (Mastura et al., 1999), and has potential anti-fungal activity against diseases of wheat (Liu et al., 2001). In China, current genetic improvement of C. camphora is mainly aimed at improving its oil content. In Jiangxi, elite types have been selected based on the chemical content of the oil in the leaves (Guo et al., 1988) and in Ji'an, Jiangxi, a nursery of elite types has been established (Liu et al., 1991). Some strains with high oil content have been selected and used in Taiwan (Jian et al., 1988).
Besides variant forms of C. camphora which have similar morphology but different proportions of the main oil components, the species has the potential for hybridization producing different chemotypes. Some other species in the genus include C. burmani, C. zeylanicum, C. fragrans, C. angustifolium, C. chekiangensis, C. subavenium, C. iners, C. microphyllum, C. mollisimum, C. porectum, C. pubescens, C. rhyncophyllum, C. scortechinii, C. sintoc and C. suvabenium. Some workers have indicated that differences in the bark and petiole could be used to differentiate species.
Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.
The species was controlled in Australia by hand pulling and intensive grazing before the dairy industry declined in the 1960s (Firth, 1981). As seeds can be dispersed by water, C. camphora should be removed from the vicinity of streams and watercourses. Expansion of the horticulture industries and closer settlement in 1980-90 helped to reduce spread of the species in some areas, and revegetation programmes for native rainforest regeneration have been advocated to reduce the spread of C. camphora. Felling of trees is ineffective because of the prolific regrowth from cut stumps Clearing of stands of camphor by bulldozer is effective, but expensive and an erosion hazard on steeper slopes. Replacement of the species with sown pasture species or native trees reduces regeneration and recolonization.
Effective chemical control is obtained by overall spraying of seedling trees up to 3 m height with triclopyr + picloram, or a strong solution of glyphosate, taking care to avoid spraying near watercourses. Established trees are killed by injecting with concentrated solutions of glyphosate, triclopyr or picloram making sure that the chemical is administered around the entire circumference of all stems below approximately 1 m from the ground (Firth, 1986).
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