Natural Distribution of Nauclea diderrichii (Rubiceae) in Semi Deciduous Forest of Togo (West Africa) and Implementation of Integrated Silviculture

Kossi Adjonou, Yaovi Nuto, Paul P. Bosu, Stephen Adu-Bredu, Adzo Dzifa Kokutse, Kouami Kokou

Département de Zoologie, Faculté des Sciences, Université de Lomé, Lomé, Togo.
Forest Research Institute of Ghana (FORIG), Kumasi, Ghana.
Laboratoire de Botanique et Ecologie Végétale, Faculté des Sciences, Université de Lomé, Lomé, Togo.

DOI: 10.4236/ajps.2014.59135                

Abstract

West African tropical forests spread from Senegal to Togo. They are considered as one of the world biodiversity hotspots. But these forests are disappearing very quickly because of human activities. In Togo, tropical forests degradation has been increased since 1980 because of improved coffee cultivation; about 67% of forests in the sub-humid mountains zone disappeared between 1978 and 2000. Facing this fast deterioration of the forests, populations begin to plant teak (an exotic species) that is the only choice proposed by local forest service. This survey consists in valuing the potentialities to restore the Togolese tropical forest using the local commercial species, recognized on the wood market. The first species retained is Nauclea diderrichii (De Wild. & Th. Dur.) Merrill, that spreads in the African tropical forest from the Sierra Leonne to Uganda and through the Congo basin. In Togo, this plant species colonises the plain of the Litimé. The objective of the present study is to analyze the distribution of the natural populations in the plain of Litimé forest but also natural and artificial regeneration of the species. The perspective is to repeat this experiment with other local species in other regions of Togo in order to diversify the plantations and to protect the local forest biodiversity.

Keywords

Litimé; Tropical Forests; Degradation; Biodiversity; Nauclea diderrichii (De Wild. & Th. Dur.) Merrill

1. Introduction

The extinction of the tropical forest is recorded everywhere throughout African continent. [1] and [2] reported that in Nigeria, the annual rate of deforestation was 285.000 ha/year between 1976 and 1980 and increased to 400.000 ha/year in the 1990s. In Cameroon, more than 200,000 ha of rainforests have been degraded over the recent years because of logging [3] . In Togo, the extinction of forests had been manifest in the 1980s when agriculture in the forest zone was directed towards the farming of improved coffee plant. Contrary to the non-improved coffee that was traditionally grown in the forest undergrowth, the improved coffee plant grows well in open areas. Because of the new constraints of production, the rainforests in the sub-humid mountainous zone of Togo [4] -[6] underwent significant reductions; about 67% were lost between 1978 and 2000 i.e. an annual rate of 3% [7] [8] . Today, the remains of these forests are located along rivers [9] or at the slopes and difficult to access.

Faced with the rapid degradation of semi-deciduous forests of the mountains of Togo [4] -[6] considered as one of the hotspots of biodiversity [10] , the reaction of the populations, regretful of past times when they were surrounded by forests, has started planting, especially with exotic species including teak (Tectona grandis). However, in this zone there are indigenous species that can contribute significantly to the forests restoration. Among the value timber species are Entandrophragma angolense, Khaya grandifoliola, Mansonia altissima, Milicia excelsa, Nauclea diderrichii, Terminalia spp. Scleroxylon Triplochiton, etc. which can widely be used in reforestation. In some neighbouring countries such as Nigeria, Ghana or Côte d’Ivoire, studies have been undertaken since the beginning of the 20th century to use these species in plantations [11] . Unfortunately, information about their ecology, their silviculture and their slow growth compared to exotic species does not encourage their use in forest plantation. However, faced with the loss of biodiversity through the excessive use of exotic plants in plantation and the high demand of indigenous species on the timber market, an effort must be done. It is in this framework that the African Academy of Sciences (AAS), in French Académie Africaine des Sciences (AAS), funded the project on “Biology, impact and integrated management of the Opepe (Nauclea diderrichii) Shoot Borer (Orgymophora mediofoveata, Lepidoptera: Noctuidae) in West Africaed” in Ghana and in Togo. Nauclea diderrichii (Nd) is a commercial value species present in the African tropical forest from Sierra Leone to Uganda through Central Africa and some parts of East Africa [12] . In Togo, it is preferably found in the Litimé plain (Figure 1). The timber, very resistant to decay, borers and termites, is used in heavy construction, in furniture, plywood and many other domestic uses. This species is classified together with iroko and mahogany. In some countries of the sub-region such as Ghana and Nigeria, it is one of the five local priority species used in plantations. [13] [14] reported that in Nigeria, Nd is the indigenous species of which the plantations are more numerous and the most successful in the supply of timber and electric poles. The species is already well known and highly appreciated by local people for its durability and the aesthetics nature of its wood.

The main objective of this paper is to assess the potential of the species in monoculture or joint farming in Togo. This study presents, more specifically, the works carried out on natural stands, the regeneration capacity and the growth of the species, a fundamental approach to the formulation of strategies of Nd integrated silviculture in Togo. It is about knowing the spatial distribution and the structure of Nd natural populations, the appropriate regeneration mode, the environmental factors promoting the growth and the adaptation of the plant to other ecosystems different from those of semi-deciduous forests of Litimé where the natural stands have been identified for the first time in Togo. Regarding the growth of the species and the control of its silviculture, the research question is to know the Nd behaviour in pure stand or in combination with commercial timber species.

2. Materials and Methods

2.1. Materials

2.1.1. Study Area of Nd Natural Stands

Litimé is located in zone IV, semi-deciduous forests domain [4] . It is part of the Volta River Basin, located on the western foothills of Akposso and Akébou plateaux. It is an area wedged between the plateau and the Buem

Conflicts of Interest

The authors declare no conflicts of interest.

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