The Ex situ Conservation of Tsoongiodendron odorum Chun (Magnoliaceae) in Nanyue Arboretum, Hunan Province, China
Volume 2 Number 2 - July 2005
Guo Cheng-ze, Guo Da-zhu and Ma Pei-shen
Tsoongiodendron odorum Chun is rare and nationally protected in China (Fu, 1992). T. odorum occurs from a latitude of 26°N southward throughout the mountain areas of subtropical China, where it grows naturally in the provinces of Fujian, Jiangxi, Hunan, Guangdong, Hainan, Guangxi, Guizhon and Yunnan. Its altitude range is from 200–1200 m. It is scattered in mountain evergreen broadleaved forests or in villages, but does not form continuous tracts (see map FIGURE 1).
Mature trees are isolated and natural regeneration is weak. Seedlings or young trees are not seen near the parent trees. There are few fruiting trees and mature seeds are frequently eaten by birds and mice. The trees grow fast, but because the tree’s trunk is straight and large; and the timber is very good and easily worked, young trees are always cut down and the roots are dug out by local residents. Thus the number or trees is becoming fewer. It is estimated that there only 80 individual trees remaining in Hunan Province and if it is not saved in time it will become extinct.
The Nanyue Arboretum has been studying this species over the last 24 years. Areas of research have included its botanic and ecological characteristics, distribution, causes of threat and the development of techniques for propagation and cultivation through seeds and cuttings. The long life of the tree makes it suitable for planting as a street tree, as an ornamental or as a lumber tree.
Seeds were collected between 1980 and 1983. These were germinated and two thousand seedlings of the species have developed into saplings. They have been planted in a plot of about 3 ha in the Arboretum that is reserved for rare and endangered species. The saplings (2003) have a mean height of 23 m with a trunk diameter of 19.6 cm (at chest height); the tallest is 24 m with a trunk diameter of 22 cm (FIGURE 2). All the trees have flowered and fruited; and each tree can produce up to 15 kg of seed each year. The seeds are used for propagation.
The seed was collected from the forest region of Gao Ze Yuan (Jiangyong county) in southern Hunan Province where it grows at elevations of 200–300 m. This region is at a latitude of 25 ºN. The soil of the site is derived from weathered sandy shale or granite. The tree grows on the fertile, deep, moist, loose soils that have a pH of 5–6.5; the surface soil layer is rich in humus. The annual mean temperature is between 18–20 ºC with a minimum temperature of -3 ºC and a maximum temperature of 43 ºC. There is a frost-free period of 300–310 days; the annual rainfall is around 1500–2000 mm and the relative humidity is 65–85 per cent. T. odorum grows with companion trees such as Exbucklandia populnea (R.Br. ex Griff) R.W. Brown, Altingia chinesis Oliver, Daphniphyllum macropodium Miq., Elaeocarpus decipiens Hemsle., Liquidambar formosana Hance and Choerospondias axillaris (Roxb.) Burtt. & Hill. To sum up, this species likes warm, moist, mountain habitats in a monsoon climate and fertile or very fertile soils.
However, even though the Rare and Endangered Plant Plot in the Garden has different conditions from the provenance area in Gao Ze Yuan and is 300 km apart, this species has been successfully cultivated in the Arboretum. It is 2.5º of latitude further north and has a higher altitude of 300–450 m. The soil derived from weathered granite turns into mountain red earth and mountain yellow loam with a lower pH of 4.5–5.5. The annual mean temperature is lower at 16 ºC, with a lower minimum and maximum temperature of -8 ºC and 40 ºC. It has a shorter frost-free period of 280–300 days; lower annual mean rainfall around 1200–1700 mm, but similar relative humidity of 60–85 per cent; and there is an annual snowfall of not more than 7 days. The plant cover of the provenance site includes Pinus massoniana Lamb., Loropetalum chinense Oliver, and Rhododendron simsii Planch.
The mature fruits (conocarpium) are picked and put in the sun for several days (Figure 3). When the walls of the fruits have broken down, the seeds are soaked in water for 3–4 days; the water must be changed every day. The pulp seed stalks become soft and are lightly rubbed with the hands; the seeds are extracted and dredged in moist sand (one part seed and three parts sand) and stored in wooden, bamboo or ceramic containers over the winter in a ventilated, shaded room. The seeds must be kept moist, and checked frequently to prevent drying out, as well as for damage by fungi or mice.
A kilo of fruit contains about 2200–2500 seeds, and about 70 per cent of these will germinate. Seedlings were grown in experimental nurseries at altitudes of 100 m, 200 m and 400 m. Seeds were sown in lines, 20–25 cm apart, 2–3 cm deep, in groups of 40–50. They are covered by a one centimeter of soil and two layers of rice straw, so the soil can only just be seen. After about two months the seeds germinate and the rice straw can be removed on a cloudy day or at dusk on a fine day. Seedling diseases and pests need to be controlled by weeding, loosening soil, good drainage to prevent water logging .
In their first year, the seedling’s mean height is 60–70 cm with a ground diameter of 0.4–0.7 cm. and they develop a good root system. Over 85 per cent of seedlings may be planted in the following spring; smaller seedlings can be kept in the seed bed for a further year.
Successful vegetative propagation has been undertaken by using cut or cleft-grafting and layering half woody cuttings in spring. The stock used was Magnolia maudiae (Dunn) Figlar. The scions taken were one year old from the canopy of the seed tree. In total about 200 plants have been grafted and 95 per cent survived.
Fu, Li Kuo (ed) 1992. China plant red data book: rare and endangered plants. Beijing: Science Press.