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Le projet majeur africain de la Grande Muraille Verte

Abdoulaye Dia
Robin Duponnois

Partie I. Espèces végétales de la Grande Muraille Verte

Potential Casuarina species and suitable techniques for the GGW

Zhong Chonglu, Zhang Yong, Chen Yu, Chen Zhen, Jiang Qingbin, K. Pinyopusarerk et Claudine Franche


Casuarina tree species belong to the Casuarinaceae family, which includes 4 genera and 96 species. Casuarina trees are native from Australia, Southeast Asia and Pacific archipelagoes. Casuarinas develop symbiotic associations with Frankia, ectomycorrhizal and endomycorrhizal fungi. They have been introduced into tropical and subtropical zones in the world. Casuarinas are economically and ecologically important. They are multipurpose tree species providing a wide range of goods and services, such as windbreaks, sand stabilization, agroforestry and general rehabilitation for difficult sites. Casuarinas can be planted as pioneer species in hot-dry river valley, dry sandy soil, rock mountain and around desert. The wood is a main source of fuelwood and charcoal, for general construction, fiber-wood, and other wood-based industries.
In this presentation, the potential of Casuarina species for the GGW will be described, together with sylvicultural techniques and Casuarina uses. A simple propagation technique that has been developed in China to produce a large number of the best Casuarina seedlings will be presented. Following field experiments, we will show that ectomycorrhizal (ECTM) or arbuscular mycorrhizal (AM) fungi or Frankia-tree genotype symbiotic associations play an important role in improved management of Casuarina forest plantations.

Entrées d'index

Texte intégral


1The family Casuarinaceae is a group of 96 species of multipurpose trees and shrubs that grow naturally in South-East Asia, Malaysia, Australia, and the Melanesian and Polynesian regions of the Pacific. Casuarinas are characterized by a conifer-like appearance due to morphologically distinctive foliage with the leaves reduced to tiny teeth on green, jointed, needle-like branchlets.

2Casuarinaceae are tolerant to adverse edaphic and climatic conditions and most species tolerate extreme heat. They grow in a wide range of different environments, from tropical forests to arid woodlands and coastal dunes. They grow in a wide range of different environments, from tropical forests to arid woodlands and coastal dunes. They frequently occur as pioneer vegetation at early stages of plant succession following disturbances such as fire, landslides, volcanic eruption and flooding. (El-Lakany et al., 1990; Midgley et al., 1983; Pinyopusarerk and House, 1993). Vast plantings of C. equisetofolia have been established in China along the coast fronting the South China Sea. They form a green belt that stretches for 3000 km and varies from 0.5 to 5km in width.

Uses of Casuarina trees

3Taken collectively, Casuarina trees have many uses (Diem and Dommergues, 1990; Diouf et al., 2008). They are capable of stabilizing shifting sand dunes, stabilizing eroding hillslopes, and reclaiming marshy soils that are periodically inundated. Because of their resistance to salt-laden winds, many species such as C. glauca and C. equisetifolia are widely used to stabilize coastal sand dunes (Zhong and Zhang, 2003). They are also planted as windbreaks to protect crops. Casuarina trees have proved to be one of the most effective shelter trees during typhoons and Tsunami in Asia. Some species such as C. equisetifolia and its hybrids grow rapidly (a growth rate of 3m per year has been reported in India) and have an attractive dense crown; consequently, these species are often planted as ornamental plants for urban beautification, parks and seaside resorts, and along roadsides.

4Another important use of Casuarina in the tropics is the production of firewood. In comparison to other fuelwood crop species, Casuarina ranks well for calorific value in relation to wood volume (about 5000 People in China use the stumps and even litter for fuel. Because Casuarina wood splits on drying, it is difficult to use the wood for lumber and furniture making. However, it can be used in rural construction as poles for house construction, electric poles and the masts of boats. The wood is very hard, with a density of 1000 kg.m3-1, and is resistant to decomposition in soil and saltwater. Thus, Casuarina poles are used in Asia for anchoring fishing nets in the mouths of the rivers. In India, the wood of C. equisetifolia is also pulped for paper, and in Madagascar, the bark is extensively used for tanning leather (Midgley et al., 1983; Pinyopusarerk and House, 1993; Diouf et al., 2008).

Potential Casuarina species for GGW

5The Casuarinaceae family includes four genera, Allocasuarina L. Johnson with 59 species, Casuarina L. Johnson with 17 species, Ceuthostoma L. Johnson with 2 species and Gymnostoma L. Johnson with 18 species (Wilson and Johnson, 1989; Turnbull, 1990). Allocasuarina is a large group of shrubs and trees, native to Australian and most of them can grow on poor soils. The potential of Casuarinaceae species for the GGW are shown in Table 1.

Casuarina Propagation Techniques

6Casuarinas can be propagated by seed, cutting and tissue culture.

Propagation from seeds

7Seed propagation is a common method used for most Casuarina species. The quality of the seedlings depends on the degree of seed maturity, the condition of seed storage and the genetic quality of the mother trees. In China, Casuarinas trees bear seeds from 3 or 4 years of age, and can continue to fruit good quality seeds for many years. The seeds are easily extracted from cones after 3-7 days under shade. Experiments in China have shown that Casuarina seeds do not store well and lose their viability after 1-2 years when stored at room temperature. For long-term storage it is suggested to store seeds at 4-5°C. At CSIRO Australian Tree Seed Centre, seeds of C. equisetifolia and C. junghuhniana still maintained good germination after 15 years of storage in cool room conditions (4-5°C) (K. Pinyopusarerk, personal communication). Each species has its optimum germination temperature, usually ranging between 20°C and 30°C. Propagation by seed takes advantage of the fact that seeds are easy to obtain, but the disadvantage is the unreliable genetic quality. To obtain seeds of high genetic quality, seed orchards or seed production areas need to be established.

Propagation by cuttings

8Water culture is now a common method for the propagation of Casuarina cuttings in China (Liang and Chen, 1982). The vegetative material is the young needle-like branchlet, preferably less than three months old taken from stock plants in hedge orchards. The procedure consists in soaking the bottom part of the 8-10 cm long branchlet in 50-100 ppm of NAA (naphthalene-acetic acid) or IBA (indole-butryic acid) solution for 24 hours. The plant material is then washed and soaked for 7-10 days in water, which is renewed every day, and placed near sunlight. At 25-32°C water temperature, cuttings will root after 7-10 days, and after 15 days, the rooting percentage is over 80%. If the water temperature is lower than 25°C, it may take 15-30 days to root. The rooted branchlets are then transplanted in growth containers filled with standard potting mix. This technique has been extended to county foresters and farmers. At present, private nursery managers can produce Casuarina cuttings using the water culture method, but they have to rely on local forest farms or research organizations to obtain new clonal genetic resources.

9Rooting in moist, fine sand, and applying the same hormone treatment than as that previously described above for water culture, is an alternative method. Generally, a sand bed 15-18 cm in depth, 80-100 cm in width and 5-10 m in length, is built with brick. A plastic sheet is placed inside the bed to keep the sand clear from soil, and water pipes are laid at one end to supply water. The sand bed is always kept moist and is covered with clear plastic sheet to increase the temperature in winter. This method is suitable for mass production.

10Both water culture and sand culture are used successfully for C. equisetifolia, C. cunninghamiana, C. glauca and C. junghuhniana. Other species such as C. cristata, Allocasuarina littoralis and A. torulosa are more difficult to root.

In Vitro Tissue Culture

11Since the 1980s, tissue culture methods have been used for Casuarinas by many workers (Duhoux et al., 1990; Abo El-Nil, 1987; Duhoux et al., 1990; Cao et al., 1990; Zhong, 2000; Liu et al., 2003). Tissues include slender branches, young buds, immature male inflorescence spikes, female flower buds and seeds. The success of the approach depends on appropriate disinfection of the plant material, the composition of the nutrient medium, rooting hormone (NAA, 6-BA or IBA), temperature, light, and the biological characteristics of the species. Generally, tissue-cultured material is easier to root than cuttings material. In 2000, Chinese researchers started to work on Casuarina in vitro. Up to now, in vitro plants of C. cunninghamiana, C. equisetifolia and C. glauca have been obtained, but there are considerable differences in organogenesis among species (Liu et al., 2003).

Inoculation of Casuarina by Mycorrhizal Fungi and Frankia

12Mycorrhizal fungi and Frankia can improve the growth and biomass production of Casuarina seedlings or saplings. Chinese researchers have been working on the selection of Casuarina symbiotic genotypes (Zhong, 1993; Zhong et al., 2003).

13Mycorrhizal fungi tree genotype associations were studied under nursery conditions for C. equisetifolia (23 provenances) and under glasshouse conditions for C. junghuhniana (10 individual families). The results of C. equisetifolia and C. junghuhniana showed that inoculation with ectomycorrhizal fungus significantly improved the diameter and height of seedlings. There was also variation among seedlots in response to the inoculation (Zhong et al., 2003).

Table 1

Table 1

Potential Casuarina species forthe GGW

14In another glasshouse study on C. junghuhniana, seedlings were inoculated with three endomycorrhizal fungi (AMF) and six ectomycorrhizal fungi (ECMF). Seedling height, root length, ground diameter, dry weight underground and above ground and total biomass were measured. The results showed that both fungi significantly improved the growth of C. junghuhniana seedlings. The AMF had a more obvious effect in improving drought resistance of C. junghuhniana than ECMF according to the nine mycorrhizal fungi used in this experiment. Five isolates were selected from the AMF and ECMF tested, including Glomus caledonium 90068, G. caledonium 90036, G. versiform 9004, Scleroderma flavidum 0207 and Laccaria sp E439. They could be used as inoculants of C. junghuhniana seedlings (Zhang et al., 2006). Since 2001, we have introduced C. equisetifolia, C. glauca, C. cunninghamiana, C. junghuhniana, C. obesa, C. cristata and A. littoralis in the hot dry river valley in Yuanmou, Yunnan Province, which is characterized by degraded soil, low annual rainfall (634 mm) and high evaporation (3848 mm). The first five species showed potential at some sites. A Frankia inoculation experiment on C. cunninghamiana was carried out in the hot dry river valley in Yuanmou, Yunnan province. Survival after planting of inoculated seedlings increased by 10.0-20.6% compared with uninoculated seedlings. Tree height after two years differed significantly among Frankia treatments. However, not every Frankia strain improved tree growth (Yang et al., 2007).

15Since 1989, many field inoculation trials have been conducted in Hainan, Guangdong and Yunnan Provinces, China. More than 18 years of experience of applying Casuarina inoculum in China have shown that application of a symbiotic microorganism (Frankia and mycorrhizal fungus) can effectively improve survival and biomass productivity of Casuarina plants and is recommended when Casuarina trees are planted at sites where Casuarinas have not previously been planted. In China, pure culture strains or isolate inoculants in liquid form are used to inoculate seedlings in the nursery. In general, seedlings or cuttings that have just developed lateral roots are suitable for inoculation.

Consideration of rehabilitation measurement and strategy for the GGW

Tree improvement

16Significant genetic variations of casuarinas trees exist among tree species, provenances, families and/or clones. Selection of appropriate Casuarina genetic resources will undoubtly lead to valuable benefits. In the GGW zones, the first criteria for selection will be trees adapted to environmental conditions, and then economic or social benefits will have to be considered. Casuarinas introduction should take benefit of the wide genetic diversity; in a second stage, casuarina tree productivity will be increased by tree improvement or selection techniques.

Sylvicultural techniques

17Water is one of the limiting factors successful to successful tree plantation. Every feasible site management practice to keep runoff water under control should be used. Short raining season is a good time to plant trees. A range of planting models should be assessed for the GGW. On degraded land, a mixed model with grass or shrub-grass or tree-shrub-grass should be tested. In the early stages, it will be very important to plant suitable tree species adapted to degraded lands. They will artificially build successful and convincing forests that will then simulate natural forest population for environmental rehabilitation.

Sustainable management and rehabilitation strategy

18The needs of local communities must be balanced with the urgent need to rehabilitate degraded land, through extensive community consultations. It will be necessary to promote technical capabilities of local citizen in all relevant management techniques and practices of vegetative rehabilitation. Another key in the success of the GGW will be to develop successful demonstrations and implement a continual program of extension and education among local communities in order to raise awareness of the importance of vegetative rehabilitation.

Conclusion and suggestion

  • Casuarina trees can be easily propagated by seeds or cuttings.

  • Casuarina trees are valuable species to improve degraded lands, which can be used as pioneer species, particularly with mycorrhizal fungus or Frankia-tree associations.

  • Casuarina trees should be considered in the GGW project.


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Table des illustrations

Titre Table 1
Légende Potential Casuarina species forthe GGW
Fichier image/jpeg, 368k


Research Institute of Tropical Forestry,
Chinese Academy of Forestry, Longdong, Guagzhou, 510520, P.R. China;

Research Institute of Tropical Forestry,
Chinese Academy of Forestry, Longdong, Guagzhou, 510520, P.R. China;

Research Institute of Tropical Forestry,
Chinese Academy of Forestry, Longdong, Guagzhou, 510520, P.R. China;

Research Institute of Tropical Forestry,
Chinese Academy of Forestry, Longdong, Guagzhou, 510520, P.R. China;

Research Institute of Tropical Forestry,
Chinese Academy of Forestry, Longdong, Guagzhou, 510520, P.R. China;

CSIRO Plant Industry, Canberra, Australia;

Institut de Recherche pour le Développement (IRD), Montpellier, France;

© IRD Éditions, 2010

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