0870-B1
M.-L. Ngo Mpeck[1], E. Asaah and Z. Tchoundjeu
The Congo Basin forests are under increasing pressure from population growth, unsustainable exploitation, poor natural resources management and other issues related to poverty and political instability. In many countries, non-timber forest products are an under-utilized resource. New agroforestry initiatives are developing techniques and strategies for the domestication and commercialization of indigenous trees whose products have traditionally been gathered from natural forests. This is being done in order to provide from farms, marketable timber and non-timber products that will enhance rural livelihoods by generating cash for resource-poor rural and peri-urban households, and also to rehabilitate the environment in degraded land.
In humid West and Central Africa, farmers have identified indigenous fruit tree species as their priority for tree domestication. Based on the pharmaceutical industries’ fears about the future of the resources, as well as researchers perception of the need for the conservation of the species and their habitats, two commercially important medicinal species, Prunus africana and Pausinystalia johimbe were added to the priority list. As these species have been classified as endangered, conservation through cultivation is important as one of several activities undertaken to preserve the species, and particularly to provide an alternative supply to limited remaining natural stands.
This paper describes the activities being carried out in the framework of the participative tree domestication approach adopted in Cameroon by ICRAF (World Agroforestry Centre) and its national partners for the domestication of these species. Propagation material collected with the assistance of farmers was used to carry out nursery experiments to assess P. africana and P. johimbe vegetative propagation ability through rooting of leafy stem cuttings in non-mist propagators. It appears that rooting leafy stem cuttings is significantly affected by the rooting factors tested; the rooting success varied from 65% to 95%. Moreover, cultivation attempts through integration of seedlings and/or rooted cuttings in different farming systems are giving promising results.
Humid lowland forest of West and Central Africa and especially those of Cameroon are undergoing an alarming rate of deforestation (WWF et al., 1992). This deforestation is threatening the day-to-day livelihood of the population that relies for their subsistence on forest products and also biodiversity in this ecosystem. Like many other tropical countries, over the past 20 years Cameroon has experienced major deforestation and forest degradation resulting from a combination of factors related to agricultural expansion, population increase and general development activities (Oyono, 1997) which has resulted in a reduction of the supply of many different non-timber forest products. Most of the trees that are of importance to land users in Cameroon’s rainforest grow in the wild since they have not been domesticated.
To prioritise indigenous species for domestication, participatory household surveys were undertaken by the World Agroforestry Centre (ICRAF) in collaboration with farmers and national research partners in Humid Lowlands of West and Central Africa (Cameroon, Gabon, Ghana and Nigeria). These priority-setting exercise identified the following species for domestication work: Irvingia gabonensis; Dacryodes edulis; Chrysophyllum albidum; Ricinodendron heudelotii and Garcinia kola (Fanzel et al., 1996).
In addition and as a result of wider consultation, and on the basis of their value as source of income in the present and future international markets, two commercially important medicinal species, Prunus africana (Pygeum) and Pausinystalia johimbe (Yohimbe), were added to ICRAF priority list (Leakey and Tchoundjeu, 2001). This arose from industrial fears about the future of these resources, as well as the need perceived by researchers for conservation of the species and their habitats.
ICRAF (World Agroforestry Centre) in collaboration with UNESCO, the Mount Cameroon Project, the Cameroon Development Corporation and the Institut de Recherche Agricole pour le Développement has initiated a participatory tree domestication programme aimed at investigating the potential of these species for agroforestry. A critical component in the participatory tree domestication strategy for these medicinal species is the development, dissemination and cultivation of improved propagules. Vegetative propagation techniques are indispensable for the capture and multiplication of the phenotypic (and possibly chemical) variation expressed by superior individuals with desirable characters (Tchoundjeu et al., 2002), This paper presents two major steps of the participatory tree domestication strategy developed for P. africana and P. johimbe. Attempts of plant propagation through rooting of leafy stem cuttings and details of integration of these species into agroforests managed by subsistence farmers are presented and discussed.
Prunus africana (Hook. F) Kalkman (Rosaceae)
This species is indigenous to the Afromontane Africa, including Madagascar. Bark extract is pharmaceutically used in modern medicine to treat benign hypertrophy hyperplasis and prostate gland hypertrophy. Wild populations are the sole source of bark and bark extract exported from Africa and Madagascar to Europe (Cunningham et al., 2002). International export demand for P. africana bark is over 3,000 tons per year; and nearly two-thirds of this is harvested in Cameroon (Cunningham and Mbenkum, 1993).
Sustainable bark harvesting is possible by removing two panels of bark from about 50% of overall circumference of the stem from the opposite sides of the stem every four or six years (Eben-Ebai et al., 1992). Unfortunately, this sustainable bark harvesting technique is not practised by bark collectors who, motivated by short-term gains completely striped the tree or cut it down to remove all the bark (Tchoundjeu et al., 2002). These destructive exploitation methods are threatening the species survival; as a result, P. africana has been classified as an endangered species by the convention for International Trade in Endangered Species (CITES) (Cunningham et al., 1997). It is estimated that about 3,500 farmers are planting P. africana seedlings in Cameroon (Cunningham et al. 2002). This practice is however, hampered by the recalcitrant nature and availability of seed (Simons et al., 1999). Chemists working for a company that was processing P. africana in Cameroon have confirmed the possibility to distinguish bark from different localities (Del Vechio, pers. Comm.). The chemical variation within (and possibly between) populations offers scope for selection and domestication.
Pausinystalia johimbe (Rubiaceae): Yohimbe
Yohimbe, is a medicinal tree, native to Africa Guinea gulf (Vivien and Faure, 1985). The bark contains a powerful alkaloid used traditionally to treat men impotence and as an aphrodisiac (Raponda-Walker and Sillans, 1961). In addition to its local widespread use as an aphrodisiac and as part of traditional healthcare system where it is used for a wide range of vascular-related ailments, the species has been long exported to Europe for Western medicine (Sunderland et al., 2000).
The current bark harvesting practice, which consists of felling and completely stripping trees, seriously reduces seed production and natural regeneration. This exploitation takes place exclusively in Cameroon and, to a lesser extent in SE Nigeria (Sunderland et al., 2000). At least 100 tons are supplied annually (120 tons) to Europe from Cameroon (Simons, 1997). Skyrocketing demand for this tree bark to supply Yohimbe-based impotence remedy manufactories, will ultimately affect future regenerative potential of the species (Sunderland et al., 2000). Pausinystalia johimbe has been even classified as endangered species by the Medicinal Plant Specialist Group of IUCN (Satabié, 1997).
Because the trees are small in diameter, very tall and clear of branches for about 70-80% of the total tree height of 20-35 meters (Thirakul, 1985), collecting seeds by climbing is difficult, if not impossible.
Non-mist propagators
Vegetative propagation of trees can be done using a variety of techniques: - rooting juvenile stem cuttings, grafting, budding, layering and in vitro tissue culture. For rooting of leafy stem, the commonly used systems in Africa is the low-cost non -mist propagator. These non-mist propagators are constructed following a design based on Howland (1975) models’, further modified as described Leakey et al. (1990). These non-mist propagators can be operated in the absence of mains electricity and a piped water supply, enabling vegetative propagation to be carried out in rural areas.
Plant material sampling and cuttings preparation
Mature and disease-free seeds of P. africana collected in North West and South West provinces of Cameroon were used to raise seedlings that were subsequently used as stock plants for vegetative propagation trials on this species.
The juvenile cuttings used for the various experiments on P. johimbe were collected from coppicing stumps from recently exploited trees of Pausinystalia johimbe in Bivouba and Lolabe villages, located in coastal rainforest of southern Cameroon. The stumps producing young shoots were 1 m height and about one year old since the trees were felled.
Experiments on Prunus africana
Experiments were designed with the aim of evaluating the effects of three key factors on the rooting of juvenile leafy stem cuttings of Prunus africana.
Sand, sawdust and a 50:50 mixture of sand and sawdust were used to evaluate the effects of rooting media on rooting of P. africana cuttings. Nine weeks after setting the cuttings, the rooting rate was slightly but significantly greater in sawdust (80%, with 20% mortality) than in sand (71%) (Tchoundjeu et al., 2002).
Five leaf areas were used as treatment” (0, 5, 10, 20 and 25 cm2) to test how rooting ability is affected by cutting leaf area. Nine weeks after the beginning of the experiment, data analysis revealed that leaf area very significantly (P < 0.001) affected the rooting success of P. africana single-node cuttings, and the rooting percentages increases with increasing leaf area. Moreover, 94% of leafless cuttings died and the remaining 6% did not root (Tchoundjeu et al., 2002)
Six concentrations of IBA were tested for their influence on the rooting of leafy stem single node-cuttings; this includes 0, 50, 100, 150, 200 and 300 IBA mg. Compared with the control, all IBA treatments enhanced rooting percentage of P. africana cuttings: but neither the mean number of roots nor the percentage of dead cuttings was significantly affected by the IBA concentrations.
Experiments on P. johimbe
Experiments were designed to evaluate the effects of three key factors on the rooting of single-node leafy stem cuttings of Pausinystalia johimbe.
Sand, sawdust and a 50:50 mixture of sand/sawdust were tested for their effects on P. johimbe rooting ability. 11 Week after setting the cuttings, rooting percentages in both sawdust (79 ± 4.6%) and the sand/sawdust mixture (75 ± 4.9%), were relatively higher than in sand (65 ± 5.4%). Definitely, it appears that rooting of P. johimbe stem cuttings is not significantly affected by variation in rooting medium, and juvenile cuttings of P. johimbe could root successfully in any of these three media (Tchoundjeu et al. in press).
To test how leaf area can affect rooting ability of P. johimbe cuttings, four different sizes of leaf areas (0, 50, 100 and 200 cm2) were tested. At the end of the experiment it appears that, leaf area had a highly significant effect on rooting of Yohimbe cuttings (P<0.001). With the exception of leafless cuttings, which rooted poorly (8.3 ± 3.6%), rooting at Week 11 was inversely proportional to the leaf area. The accumulated rooting percentage at Week 11 for cuttings with 50, 100 and 200cm2 leaf area was respectively 86.7 ± 4.4%, 76.7 ± 5.5% and 70 ± 6%. Similarly, the effects of leaf area on the number of roots formed were significant (Tchoundjeu et al., in press).
Five concentrations IBA were tested for their effects on rooting of Yohimbe leafy stem cuttings: 0, 50, 100, 150 and 200 IBA µg. The data analysis indicated that IBA treatments significantly (P <0.001) accelerated rooting of Pausinystalia johimbe leafy stem cuttings. The rooting percentage at week 11 for cuttings with 50, 100, 150 and 200 µg IBA was 60 ± 6.4%, 76.7 ± 5.6%, 85 ± 4.6% and 95 ± 2.8%, while the rooting percentage of the untreated cuttings was 36.7 ± 6.3% (Ngo Mpeck et al. in prep).
Integration attempts of these medicinal species propagules into existing cropping systems have been preceded by consultations with farmers to develop a joint objective for such trials. In some cases, cuttings and seedlings raised in on-station nurseries were provided to farmers for planting. In such trials, farmers often avoided planting in the forest where the species occurs naturally, but planted in their farms to justify their ownership on the future trees. The objectives of these trials are generally simple and often aims are:
- evaluating the performance of improved propagules (P. johimbe and P: africana) in different cropping systems; and
- assessing the compatibility of these propagules with companion crops found in the existing farming systems of its natural range.
P. johimbe cultivation trials were established in a plantain and in a mixed-crop field in a participatory approach: the farmer providing the land, is responsible of clearing and planting the food crops. Researchers conceived the design of the experiment and the trial were established 6 months after planting the plantains or one month after mixed-crop planting (Cassava, maize, groundnut, cucumber).
A year after planting cuttings, the mortality rate was null in the experiment set in the plantain farm, while the mortality rate was about 10% in the mixed-crop field. The results 24 months after planting are promising with growth height in plantain farm ranging from 0.44 m to 1,80 m recorded. Data analysis revealed no significant difference in the growth of seedlings and cuttings in mixed-crop field, plants’ height ranging from 15 to 95 cm.
Mean height increments during the first two years were greatest for cuttings in the plantain farm compared to those in the mixed crop field. This resulted into a more visible tendency of these cuttings to develop multiple stems: food crop plants probably slowed the growth of Yohimbe plants. In the mixed-crop field, young P. johimbe plants served as important nurse supporting climbers (such as cucumbers); in some ways these plants have strangled the cuttings and seedlings and reduce their effective growth. This is one of the constraints encountered in working on-farm especially as trials cannot be monitored like on-station trials. These preliminary results are however, indicating that Pausinystalia johimbe could grow along with others crops in the farming systems in its natural habitat. This is a substantial growth for a tree known as slow growing, and without any chemical fertilisation.
Similar experiment was designed for P. africana cuttings and seedlings planted in a food crop farm of maize and plantain.
A year after planting, no statistical differences were observed in the survival rate, mean growth height and circumference (using collar diameter) of both cuttings and seedlings of P. africana. Survival rates were 100% for both propagules; mean growth height ranged from 1.7 m (cutting) to 1.8 m (seedling). While mean circumference ranged from 0.61 m to 0.8 m respectively.
At 2 and 3 years after planting, some changes though not statistically (P> 0.05) significant are visible. Survival rates for cuttings and seedlings dropped to 96.39% then to 90% (cuttings) and 57% for seedlings in the third year.
Mean growth height of cuttings ranged from 2.38 to 4.41 m. Circumference ranged 1.3 to 4.5 cm in second and third year respectively. A similar increment was recorded for seedlings with mean growth height ranging from 2 m to 2 53 m and circumference varied from 0.8 to 3 cm in the second and third year respectively.
The present experiments clearly indicated that it is possible to multiply P. johimbe and P africana by rooting juvenile material. Vegetative propagation could provide an alternative, which would permit propagation of this species throughout the year and possibly facilitate cultivate the species. These results are an important input into the development of an appropriate local strategy for conservation through cultivation of this species already classified as endangered by IUCN and CITES. In Cameroon as in other tropical countries, where deforestation has caused significant loss of native biodiversity, integrating local tree species in traditional farming systems appear as a form of genetic resources conservation through cultivation, especially because traditional farming systems such as home gardens have been identified as important in situ germplasm banks of semi-domesticated plant species.
Cunningham, A.B. & Mbenkum, F.T. 1993. Sustainability of harvesting Prunus africana bark in Cameroon. A medicinal plant in international trade. People and Plants Working Paper N0 2, 28 p.
Cunningham, M, Cunningham, A.B. & Schipmann, U. 1997. Trade in Prunus africana and implementation of CITES. German Federal Agency for Nature Conservation. 52 p.
Cunningham, A.B., Ayuk, E., Franzel, S., Duguma, B. and Asanga, C. 2002. An economic evaluation of medicinal tree cultivation: Prunus africana in Cameroon. People and plants Working paper 10. UNESCO Paris.
Eben-Ebai, S., Ewusi, B., Asanga, C. and Nkongo, J. 1992. An evaluation of the quality and distribution of lity and distribution of Pygeum africanum on the slopes of Mount Cameroon, 24 p.
Franzel, S., Jaenicke, H. & Janssen, W. (1996). Choosing the right trees: setting priorities for multipurpose tree improvement. Research Report No 8. ISNAR, The Hague, The Netherlands. 87 p.
Howland, P. (1975). Vegetative propagation methods for Triplochiton scleroxylon K. Schum. Proc. Symp. On Variation and Breeding Systems of Triplochiton scleroxylon K. Schum. Federal Department of Forest Research, Ibadan, Nigeria. Pp 99-109.
Leakey, R.R.B. and Tchoundjeu, Z. 2001. Diversification of tree crops: domestication of companion crops for poverty reduction and environmental services. Expl. Agri. 37: 279 - 296.
Leakey R.R.B., Mesén, J.F., Tchoundjeu, Z., Longman, K.A., Dick, J.McP., Newton, A., Matin, A., Grace, J., Munro, R.C. and Muthoka, P.N. (1990). Low-technology techniques for the vegetative propagation of tropical trees. Commonwealth Forestry Review, 69: 247-257.
Ngo Mpeck M.-L., Tchoundjeu, Z. and Asaah, E. (In preparation). Vegetative propagation of pausinystalia johimbe (K. Schum) by leafy stem cuttings: effects of IBA concentration, cutting stem length and node position on rooting ability.
Oyono, P.R. 1997 - Ruptures socio-économiques et surexploitation du palmier Raphia par les populations forestières de Lomié (Sud-Est Cameroon). Arbres, Forêts et Communautés Rurales, 11: 27-33.
Raponda-Walker, A. & Sillans, R., 1961. Les plantes utiles du Gabon. 614 p.
Satabié, B. 1997. Cameroon flora biodiversity. IReport of the Planning Workshop on “National Biodiversity Strategy and Action Plan” under the convention on Biological diversity, pp 43- 48. Limbe, Cameroon, 16-18 June 1997.
Simons, A.J. (1997). Cameroon trip report. 1-10 May - ICRAF, unpublished report. 2 p.
Sunderland, T.C.H., Tchoundjeu, Z. and Ngo-Mpeck M.L. 2000. The exploitation of Pausinystalia johimbe. Medicinal Plant Conservation, 6: 21-23.
Sunderland, T.C.H., Ngo-Mpeck M.L., Tchoundjeu, Z. (in press). Potential for domestication of Pausinystalia johimbe. Economic Botany.
Tchoundjeu, Z., Ngo Mpeck, M-L., Asaah, E. and Amougou, A. (In press). Contribution of vegetative propagation to the domestication of Pausinystalia johimbe (k. schum), a highly threatened medicinal species of Cest and Central Africa. Forest Ecology and Management.
Tchoundjeu, Z., Avana, M.L., Leakey, R.R.B., Simons, A.J., Asaah, E., Duguma, B. and Bell, J.M. 2002. Vegetative propagation of Prunus africana: Effects of rooting medium, auxin concentrations and leaf area. Agroforestry Systems 54: 183-192.
Thirakul S. 1985. Manuel de dendrologie. Groupe Poulin. Theriault Ltee, Quebec, Canada. 640 p.
Vivien, J. & Faure, J.J. (1985): Arbres des forêts denses d’Afrique Centrale. Agence de la Cooperation Culturelle et Technique, 565 p.
WWF, The Nature Conservancy, and World Resources Institute. 1992. Central Africa: Global Climatic Changes and Development. Washington, DC: USAID.
| [1] Corresponding author: International
Centre for Research in Agroforestry (ICRAF), P.O. Box 2067, Yaoundé,
Cameroon. Email: [email protected] |