HARVESTING OF IRVINGIA GABONENSIS AND IRVINGIA WOMBULU IN NIGERIAN FORESTS; POTENTIALS FOR THE DEVELOPMENT OF SUSTAINABLE SYSTEMS

Mr. David LADIPO
Centre for Environment, Renewable Natural Resources Management, Research and Development (CENRAD)
IBADAN
Nigeria

(Not available in French & Russian)

Abstract

Irvingia gabonensis and I. wombulu; the bush mango are the sources of ‘Ogbono’ , the Irvingia kernel which is popularly used as soup thickener in most West African countries. Less than 10% of the total annual crop of the fruit or the kernel is harvested from planted trees while the rest are collected from natural forests. Harvesting or collections in the forests are activities of women and children. They are also responsible for processing and substantial amount of marketing.

Irvingia kernel is now major export produce to Europe and the USA. The popularity of Irvingia kernels in the local and international markets has given it the potentials for a true commercial crop, with this resulting in more intensive collection in the forests.

Recently, an attempt at setting local quality standards for the kernels in trade has commenced. Standardization of this will help export promotion and the increase of financial returns to the rural farmers who collect from the forests and manually process (nut extraction) and sun dry for storage before marketing.

The various initiatives of ICRAF, NACGRAB and CENRAD on the collection of the remaining genetic resources of Irvingia in West Africa, its establishment in genebanks and the potentials to utilize selected lines in new planting provides hope for the future. It is believed that this will provide the seed for the sustainable production of Irvingia as deforestation and old tree age is already affecting wild resources.

Pure stand plantations and trees in agroforestry systems are attractive. Multistrata agroforestry system for production is presently being established in Nigeria within the southern forest zones where bush mango is well known.

Introduction

Nigeria is a densely populated country with a population of about 120 million people. This country's dense population and its relatively enhanced economic development has resulted in vast increase in demand for food.

Nigeria is a diverse country socio-culturally and it is the same situation with its forest and forest resources particularly the extractive resources. Based on the 1993/95 land-use and vegetation assessment, there are nine ecological zones from the mangrove forests in the south to the Sahel in the far north (see Fig. 1). All these ecological zone are rich in non-timber forest resources and they are equally different and diverse. There are over 180 non timber forest resources already described (Okafor 1988) but there are still a lot more. Recent estimates give 640 as the total figure including those newly described for medicinal uses and sources of natural colours.

Figure 1

ECOLOGICAL ZONES OF NIGERIA

These NWFP include:

Chrysophyllum albidum (the African star apple)
Dacryodes edulis (the African bush pear)
Tetrapleura tetraptera
Xylopia aethiopiaca
Parkia biglobosa
Pterocarpus milbraedi
Pterocarpus erinaceus
Baionella toxisperma
Garcinia kola and
Irvingia spp to mention a few

The high forest in the South contains more non timber resources than the other forest types. It is now realized that forests are a trategic source of food and other products for man.

Many plants, important for food and income in Nigeria, as it is the case in many other Africa countries (Ladipo 1988) are sourced from Nigerian forests. Despite the importance of our forests, Forests in Nigeria are under great pressure. These pressures have led to large destruction of natural forests and it is estimated that 5% of closed forests are cleared annually for other uses with negative repercussions. (Kio et al. 1989) FORMECU (1995) reports a significant increase in forest degradation in Nigeria with increase in desertification, savanarization and the forest which were erstwhile referred to as being rich in timber and non-timber resources are being turned into poor degraded forests that are poorer in species; especially those that could be useful for food in medicine, industry and agriculture. Particular concern are for those non-timber forest resources valuable for indigenous consumption and on which local food security depends.

These non-timber forest resources are sourced through seasonal extraction from the forests. Forest extractivism is an old enterprise in the forest areas of Nigeria. It is more active in the Southern forests where forest people live almost entirely on the forests and their products.

Forest people have substantial indigenous knowledge on the quantities of there NTFP in the forests and also on the phenology of production.

Many farmers can even predict mast years and good and bad trees are recognized.

Food gathered and hunted in the wild are important, and they will continue to be important in the diet of may forest or farming families in Nigeria (Ladipo 1998).

Irvingia Species

Irvingia gabonensis and Irvingia wombolu are two of these non-timber forest resources which in recent times have become very important products. (See fig 2). The present paper reports their extraction from Nigerian forests, and discuss, potentials for their sustainable production.

The Irvingia gabonensis is the eating type which produces sweet/flesh (mesocarp). This is eaten fresh while the stone is usually split to reveal its kernell: the product that is used for soup thickening. The Irvingia wombolu is the type that has non-edible flesh. The flesh is sour and the fruit stone is also extracted to produce the kernell (ogbono). It is common to mix the two types of kernels. There is not much differences between the two species except for fruit sweetness and some tree morphological differences. The high demand situation for bush mango kernels has resulted in excessive exploitation in the bush at such a rate that the sustainability of these natural resources has been the concern of various workers (NRC 1991) particularly with the continued clearing and selective exploitation of forests, (Palmberg 1984).

Figure 2

The Irvingia fruit

	A drupe (stone fruit) Usually one seeded. Fruit consisting of 3 distinct layers skin, flesh and stone (seed).
	Stone/Seed Coat (fibrous) can be split into two by force when dry
	Fruit adopted for dispersal by mammals i.e. Irvingia robur

The Irvingia Tree

Irvingia gabonensis (Aubry -Lecomte ex O" Rouke) Baill, the bush mango is a medium sized evergreen tree but large specimens are not uncommon in the natural forest from where a substantial quantity of its fruit or seed is still being sourced in Nigeria.

It belongs to the family Irvingiaceae (order-Rutales) a small tropical family containing two other genera (Klaiedoxa, Desbordesia) and the genus Irvingia which contains three species (see table 1) all occurring in West and central Africa.

Two varieties of Irvingia gabonensis have been identified (Okafor 1975) based on long phenological and reproductive phenological observations. He reported between these varieties in flowering and fruiting (Table 3), but it is now known (Ujor pers comm.) that flowering in this species could vary from site to site particularly when these are ecologically different. The examples of Enugu (derived savanna) and Onne (High forest) in Nigeria were cited.

The vegetative and reproductive structures of I. gabonensis has been described by Keay (1989). However, flowers are yellowish to greenish white in slender clustered racems or small panicles and ripe fruits yellowish-green to orange colour when ripe. (see Ladipo et. al. 1996)

Table 1

Members of the genus Irvingia in Nigeria

Popularity of Irvingia Species

Irvingia gabonensis I. wombolu or their kernels; the food product are very well known in Nigeria and in the West African subregion, particularly in Togo, Dahomey, Cote d'Ivoire and Sierra Leone where fruit pulp and kernels are used as food (Okigbo 1981). Other uses of this socio-economically important fruit crop (Agbor 1986) are shown on table 2. These range from their use as food to medicine and environmental conservation including use as windbreaks in plantains of banana or in plant in production systems. Irvingia is well know amongst all the sourthern tribes, but its use as food (edible fruit and soup thickener) has become accepted all over Nigeria, and amongst even tribes that have never seen the tree.

The popularity of Irvingia gabonensis fruit also encompasses age classes as old, mature and the adolescent and juveniles like the fruit a lot.

Trade in Irvingia Kernels in Nigeria

Irvingia kernels (ogbono is produced in the Southern forest area of Nigeria, (see Fig. 3) and trade in this commodity is immense in the country. Ladipo and Boland (1994) reported on extensive trade in the kernels within the Southern forest area and between this area and the northern Savanna areas. Kernels are transported to the North of Nigeria by whole traders (see Fig 4), and these are also traded internationally to various other countries (see Fig. 5). The immense commerce that has been built on this produce shows its importance in the economy of the producers (the farmers/collectors). Trade in ogbono to EEC countries and to the USA continues to grow with results obtained in airports, through where they are transported out. Recently efforts to standardize and to develop quality standard have commenced (Ladipo 1998). If the recommended system are followed it will be possible to get Irvingia kernels to higher levels of international trade and utilization.

Table 2

Uses of Irvingia gabonensis and Irvingia wombolu in Nigeria.

Nutritional values of Irvingia Kernels

The consideration of Irvingia as a strategic ‘crop’ and one that has immense value for food security cannot be over emphasized if we consider its nutrient values. This is very important where resource poor farmers are involved and whose diet revolves mainly around starchy foods such as those made from cassava and yams (Discorea species) etc.

Eyo (1981) after Okafor and Okolo (1974) and Eka (1979) looked at the nutrient values of Irvingia kernels in comparison with other species from Nigeria. He reported that Irvingia is an important oilseed, and a very nutritious one too. The nutrient values are shown on table 3, for starch, protein and its amino acid content.

Table 3

Nutrient content of Irvingia kernels (Eyo 1981).

Figure 3

Figure 4

International trade routes of Irvingia gabonensis (‘Ogbono’) in West Africa.

Forest production (collection) of Irvingia fruits in Nigeria

Irvingia species can be found, as earlier said, in the high forests and in transition forest area. They are specifically also found in compound farms and these days it is not uncommon to find Irvingia protected in Cocoa-cola and coffee plantations. However, Irvingia fruits, for fresh eating and for their kernels are collected from the wild forest (60%) and from the compound farm garden 10% and the outlying fields (30%). Within the high forests areas, many families depend on this enterprise for survival.

Agbor (1986) also reported on an economic assessment of Irvingia gabonensis, in Cross River State in Nigeria. He reported that a large quantity of Irvingia kernels are produced in the State but he never gave figures to back this conclusion up.

Agbor (1986) concentrated on the high density areas of Irvingia i.e. Ikom, Obubra, Akampa, Odukpani, and Calabar. Field collection of Irvingia from the wild take place between December to April (Irvingia wombolu) and between June – August (Irvingia gabonensis).

Estimates of production in a good year shows that over 750,000 tons of Fresh fruits are collected annually from the high forest zones, from all sources and this means 120,000 tons of kernels, which are then dried to help their storage.

This figure does not include the processed kernels which are imported into Nigeria from other countries in west and central Africa. With these, over 1.2,000,000 tons of Irvingia kernels are marketed in Nigeria, with this representing about 40% West Africa total production.

Collectors of Irvingia can be classified as follows; forest collection of Irvingia falls into groups:

1. Children and women, and
2. Young Adult (males.)

The children and women are restricted to the compound farms and to near village forests where they make daily runs to collect fruits from specified trees.

The young Adults (males) are involved in ‘long-term’ field collection. This group go into the forest for two weekly fruit collections trips and they usually process the fruit in the bush so as to reduce the laod to be carried out to the villages at the end of the collection trips. Extraction of near home materials are usually the assignment for females (the mothers) and children both male and female.

Developments of Sustainable production of Irvingia gabonensis in Nigeria

This paper will attempt to look at the development of a sustainable system for Irvingia from the angle of conservation and production where viable production and conservation are achieved at the same time. In other words, for the product of Irvingia to be sustainable, we need to be able to maintain sufficient product of Irvingia in its season while the genetic resources of the species are adequently consumed and protected. This initiative requires immense ‘human action’. The research campaign of the international centre for Research in agroforestry (ICRAF) is relevant here (see Ladipo et al 1996). In addition to the above, ICRAF has embarked on a programme of genetic resources collection and conservation and the utilization of high value materials of Irvingia in agroforestry systems. The values of the multistrata system have been emphasized and this is the system that CENRAD has practised. Marcotting (air layering) and the product of seedling stocks selected from high value mother trees, new trees of Irvingia have been planted in farmers fields. It is proposed that these trees and the other flora will mature into viable multistrata system in the various ecologies where this has been practised. The present effort will definitely reduce the pressure on Nigerias natural forest trees, and the enhancement of product from the high value plantings in fields and compound farms where the resources have been tried out.

Needs for the future

To ensure a viable and sustainable production system of Irvingia in Nigeria, we will require to further understand (research) the socio-economics of Irvingia in Nigeria. It will further be useful to adequately know the product demand situation in Nigeria so we can put in place proper and viable new ‘supportive’ plantings in the degraded forests.

In addition to the above we require to try the old systems of enrichment planting which will support the ecological status of the forests and also enhance its productivity (Irvingia kernels). Be these as they may, the need for the establishment of pure commercial plantations will help and ensure sustainable production of Irvingia in Nigeria, through, at the reduction of the pressure on the natural forest as population and external demand grow. We need to remind ourselves here that the various non-timber forest resources (NTFPs) which are being addressed today were sustainally extracted from the forest by farmers in the past, when population was not as high as it is today.

References

Agbor L. O. N. (1986). Economic assessment of Irvingia gabonensis in Cross River State of Nigeria. Msc dissertation Dept. of Forest Resources Management University of Ibadan. Ibadan. Nigeria. pp 160.

Ladipo D. O., J. M. Fondoun and N, Ganga (1996). Domestication of the bush mango (Irvingia spp): some exploitable intra specific variations in West and Central Africa. In proceedings of an FAO ICRAF-IUFRO proceedings (Non-wood Forest Products FAO NO 9).

Domestication and Commercialization of non-timber forest products in agroforestry system. Eds. Leakay RRB, A. B. Temu, M. Melnyk and P. Vantomme pp 297.

Ladipo D. O. and Boland D. (1994). Trade in Irvingia kernels. Paper presented at the International workshop on Irvingia in West and central Africa International centre for Research in Agroforestry (ICRAF) 4pp.

Eyo E. S. (1981). The composition of carbohydrates and proteins in the seeds of Irvingia gabonensis, Cucumeropsis manii and mucuna sloanei from Nigeria. Plant Research and Development (Institute of Scientific Cooperation) pp 107 – 113.

Okafor J. C and Okolo H. C. (1974). Potentials of some indigenous fruit trees of Nigeria. Paper presented at the 5th Annual Conference of the Forestry Association of Nigeria Jos (1974) pp 60–71.

Hyman E. L. (1995). Technology and the Organisation of production, processing and marketing of non-timber forest products. In Proceedings: current issues in non-timber forest products Research Ed. Perez M,R, and Arnold J.E.M (1995) pp 197.

Kio P.R.O., B. A. Oguntala, D. O. Ladipo and FOC Nwonwu (1989). An analysis of the development of management systems in Tropical moist forest of Nigeria in management of Tropical moist forests in Africa FAO forestry paper NO 88 FAO. Rome pp 109 – 134.