Is the Paper Bark tree becoming invasive in Hong Kong?
by Billy Hau
Melaleuca quinquenervia (Paper Bark tree) is a famous invasive species in sub-tropical wetland habitats. It is one of the "One Hundred of the World’s Worst Invasive Alien Species" identified by the Invasive Species Specialist Group (ISSG) of IUCN (http://www.issg.org/database/welcome/). It is native to Eastern Australia, New Guinea and New Caledonia in open swampy areas. It was first introduced into Florida in 1900 and is now a major wetland pest. It currently infests over 202,000 ha of wetlands in south Florida of which 10,000 to 20,000 ha are monocultures (Turner et al., 1998). Studies in Florida have shown that the distribution of this species is limited more by suitable habitat and the presence of seed than by climate and the two key factors for the spread of this species are fire and wetland (Turner et al., 1998). Apart from invading marshlands such as sawgrass prairies, M. quinquenervia trees can invade many artificial areas such as canal banks, roadsides, pastures, and urban areas. Fire does not usually kill M. quinquenervia trees because resprouting or coppicing branches enable burnt trees to survive and fire induces the serotinous fruits or capsules to release many tiny seeds, which are dispersed by wind and water (Turner et al., 1998). Seed germination and seedling establishment on the resultant fertile ash bed are promoted by the more open canopy after burning.
M. quinquenervia were introduced into Hong Kong from eastern Australia in the late 19th century as ornamental trees in gardens. It was first planted in the wild in 1897 (Ford, 1898). About 200 seedlings were planted in the vicinity of Kennedy Town Hospital. Since then, it has been planted in large numbers annually (Corlett, 1999). It was one of the 10 key pioneer species commonly used by the Territory Development Department in the restoration of degraded lands in Hong Kong in the late 1980s and early 1990s (Chong, 1999). However, it was found not to grow well on dry, upland slopes, and is no longer a significant species in woodland planting mixes (Liz Leven, pers. com.). Hong Kong has a similar climate to south Florida and eastern Australia, with distinct dry and wet seasons and plenty of anthropogenic hill fires. Yet, there has been no report of this species becoming invasive in Hong Kong. It is believed that M. quinquenervia cannot reproduce successfully or its seedling cannot establish itself naturally in Hong Kong. However, Dr. Ng Sai Chit and I have recently discovered a patch of 30 to 40 mature M. quinquenervia trees (over 10m in height) in a fire-maintained shrubland in Ho Sheung Heung, Sheung Shui with lots of young seedlings ranging from less than a metre to over 2 metres. Those seedlings are randomly distributed at that site and unlikely to have been planted. We suspect that wild fire triggered the release of seeds from the mature trees and the seedlings have somehow overcome the environmental barriers even in the absence of wetlands in that site.
Without a more widespread survey, I cannot say that M. quinquenervia is becoming invasive in Hong Kong but it surely has the potential to be so. Fortunately, it is no longer planted in any significant numbers in our countryside but those existing patches should be monitored according to the IUCN guideline on invasive species (ISSG, 2000). In addition, two other introduced tree species of concern are Casuarina equisetifolia and Acacia auriculiformis. Both species are still widely planted in our countryside. Natural recruitments of C. equisetifolia have been noticed in a number of places. Bulbuls were recently seen taking the seeds of A. auriculiformis enhancing seed dispersal (Richard Corlett, pers. com.). And although there are no reports of these two species as invasives in any parts of the world, their fast growing habits and the ability to reproduce naturally in Hong Kong is reason for concern. Any reports from Porcupine! readers of natural recruitments of M. quinquenervia, C. equisetifolia and A. auriculiformis in Hong Kong are welcome.
Chong, C.L. (1999). Restoration of degraded lands in Hong Kong. In: Wong, H.M., Wong, J.W.C. and Baker,A.J.M. (eds),. Remediation and Management of Degraded Lands, Lewis Publishers: Boca Raton, London, New York, Washington, pp. 185-193.
Corlett, R.T. (1999). Environmental forestry in Hong Kong: 1871-1997. Forest Ecology and Management 116: 93-105.
Ford, C. (1898). Report of the Superintendent of the Botanical and Afforestation Department for 1897. Government Notification No. 273, pp. 601-609, The Hong Kong Government Gazette, 18th June 1898.
Invasive Species Specialist Group (ISSG). (2000). IUCN Guidelines for the Prevention of Biodiversity Loss Caused by Alien Invasive Species. IUCN, Gland, Switzerland.
Turner, C.E., Center, T.D., Burrows, D.W., and Buckingham, G.R. (1998). Ecology and management of Melaleuca quinquenervia, an invader of wetlands in Florida. U.S.A. Wetlands Ecology and Management 5: 165-178.
Hong Kong vascular plants: a new record and clarification of a name
by Ng Sai-chit, KFBG
Symplocos cochinchinensis (Lour.) S. Moore var. cochinchinensis
In J. Bot. 52(6): 148-149, 1914; Wu R.-F. & H.P. Nooteboom, Flora of China 15: 248-249.
On a trip to Tai No Village near Ho Chung, Sai Kung, with Ken So of KFBG on 11 September 2001, Ken spotted three fruiting Symplocos trees up to 15-20 m in the feng-shui woodland behind the village. Attempts to collect a fruiting specimen were unsuccessful but the shape of fruit and infructescence were noted, and a specimen without fruits or flowers were collected (S.C.Ng, 3147 (AFCD, HKU, KFBG)). The plant was finally identified as Symplocos cochinchinensis var. cochinchinensis using the key and description in Wu & Nooteboom (1996), and this identification was confirmed by comparison with specimens collected from Hainan (Anon. s.n. (HK 18069), 18 June, 1893, Hainan (AFCD); A. Henry s.n. (HK18074), 1889, Hainan (AFCD)). No earlier records of this variety in Hong Kong have been found.
This variety is remarkable among Hong Kong’s Symplocos spp. in that it has persistent and dense, soft brown to reddish brown, hairs on the young shoots and undersides of the leaves, which are visible at a distance. Although it has a spike-like infructescence which may branch at the base and globose to ampuliform fruits similar to the supposedly related S. cochinchinensis var. laurina (Retz.) Noot., these two varieties of Nooteboom appear different enough to be considered as distinct species, as they have previously been (Wu & Huang, 1987). This variety is very rare in Hong Kong and is so far only known from the above locality. Regionally it is widespread and has been recorded in South China, India, Indochina, S.E. Asia, and Japan.
Carex bodinieri Franch.
In Bull. Soc. Philom. Paris 8 sér 7: 85, 1895; Anon., Flora Reipublicae Popularis Sinicae 12: 445, 2000.
Carex brunnea auct. non Thunb.:
Xing, Ng, & Chau, Memoirs of the Hong Kong Natural History Society 23: 113, 2000.
Three Hong Kong specimens which had previously been considered as Carex brunnea (Anon. s.n. (HK8213), 22 September 1909, exact locality unknown (AFCD); S.C. Ng 1552, Pik Uk, 5 November, 1998 (AFCD, HKU); S.C.Ng 2810, 4 November 2000, Nam Fung Road, (AFCD, HKU)) were identified as C. bodinieri. This was confirmed by comparing with Chinese and Japanese specimen deposited at the Beijing National Herbarium (PE) and the description in Dai & Liang (2000) which also mentioned Hong Kong as the type locality for the species.
Carex bodinieri differs from C. brunnea in having more or less glabrous utricles with a hispid margin, whereas C. brunnea has white, minute, coarse rigid hairs on both sides of the utricle as well as on the margin. When fully ripe, the achene of C. bodinieri has convex faces on at least the abaxial side, whereas that of C. brunnea is slightly concave at the middle. The spike of C. brunnea also tends to have denser utricles than C. bodinieri. Locally in Hong Kong, C. bodinieri has been seen by me at Ho Chung and Aberdeen only, but it is usually locally abundant where it occurs. Regionally it is widespread and has been recorded over S. China and Japan.
Carex brunnea was first mentioned to occur in Hong Kong near Magazine Gap in Dunn & Tutcher (1912), which did not specify the specimen this record was based on. It has since then appeared in the local checklist (Anon., 1978, 1993), and in Shaw (2000), which for the first time mentioned a Hong Kong specimen (HK Expedition HK 7187, October 1909, Magazine Gap) that may be at Kew. Without seeing the specimens used by Dunn & Tutcher (1912) and Shaw (2000), I am unable to confirm whether they are also misidentifications of C. bodinieri.
Anonymous. (1978) Check List of Hong Kong Plants. Agriculture and Fisheries Department Bulletin No. 1 (Revised), Hong Kong Herbarium, Hong Kong.
Anonymous. (1993) Check List of Hong Kong Plants. Agriculture and Fisheries Department Bulletin No. 1 (Revised), Hong Kong Herbarium, Hong Kong.
Dai, L.-K. and Liang, S.-Y. (eds.) (2000) Carex. Flora Reipublicae Popularis Sinicae. Volume 12.
Dunn, S.T. and Tutcher, W.J. (1912) Flora of Kwangtung and Hongkong (China). Royal Botanic Garden, Kew.
Shaw, J.S. (2000) Hong Kong Cyperaceae: Taxonomy, Ecology and Geography. M. Phil thesis. The University of Hong Kong.
Wu, R.-F. and Huang, S.-M. (eds.) (1987) Symplocaceae and Styracaceae. Flora Reipublicae Popularis Sinicae. Volume 60 (2).
Wu, R.-F. and Nooteboom, H.P. (1996) Symplocaceae. Flora of China. 15: 235-252.
Xing, F.-W., Ng, S.-C. and Chau, L.K.-C. (2000) Gymnosperms and angiosperms of Hong Kong. Memoirs of the Hong Kong Natural History Society. 23:21-136.