1. Introduction

There is a plethora of literature on the socio-economic potentials of Non-Timber Forest Products (NTFPs) as an important component of the livelihood strategies of people living in or adjacent to forest areas[1-5]. The growing number of reports has suggested that hundreds of millions of people world-wide currently derive a significant portion of their subsistence needs and livelihoods from gathered plant and animal products. For most of the world's rural households, NTFPs provide essential food and nutrition, medicine, fodder, fuel, thatch and construction materials, mulch and non-farm income. It was estimated by the Food and Agriculture Organization of the United Nations that the total value of internationally traded NTFPs for the year 2002 was about 5.56 trillion US Dollars for fifty five species assessed[6].

Despite the known and substantial economic value of few individual NTFPs, and the unknown, but likely high economic value of NTFPs in aggregate, forest managers havehistorically not included them as important factors in forest management. But not only do NTFPs comprise a significantpart of the biological diversity of forest ecosystems, they are integral element of sustainable forestry[7]. Non-Timber Forest Products are particularly important in ensuring food security, maintaining nutritional balance in people’s diets and contributing to health care system. They are also essential to human survival during famine and ‘hungry season’ (period when most agricultural crops are not yet matured)[5]. At other times, NTFPs serve and support income-earning activities in both rural and urban economies.

Forest management for NTFPs can provide a continuing source of livelihood and help to maintain the forest resource for future generations. It has been argued that establishing extractive reserves for the sustainable harvest of marketable NTFPs has the potential to unite economic and conservation goals by promoting nature conservation while maximizing long-term economic returns per unit area[8-10]. Nonetheless, it is noteworthy that the management of forest lands is complex, and this is never more so than when considering many competing and non-complementary uses for the same area of forest.

Among the key uncertainties in the sustainable management of forest for NTFPs is the high diversity of species and paucity of information on indigenous use pattern. For instance, there are indications that Nigeria has more than six thousand NTFPs growing in the wild[11]. However, there is no complete list of NTFPs in the country because most biotic species from which forest products are derived are not well documented[2]. Increasing population coupled with large scale depreciation as a result of shifting cultivation, bush burning, logging and forest conversion have continued to pose concern about the sustainability and need for conservation of these species. Similarly, inadequate information on the ecological productivity, growth forms, life history and maintenance of the various species used as NTFPs further complicate management scenarios and the setting of conservation priorities for this category of forest products[12]. Therefore, in the design of appropriate strategies for sustainable management of non-timber forest products, it is important to identify species with the potential for sustainable and profitable extraction in a managed system.

Since the economic importance of NTFPs are often reflected in the social and cultural values placed on the products, in this study we carried out a socio-economic survey of NTFPs commonly utilized and found within the tropical lowland rainforest of Omo Forest Reserve, southwestern Nigeria. The rainforest of Omo has been identified as of high priority for conservation attention on a continental scale[13]. In addition to being a reservoir of an enormous quantity of plant and animal species, the forest reserve also constitute an integral part of the rural economies within which it subsists. Given that the importance of NTFPs is location-specific and dynamic, and because local use of non-timber forest resource varies greatly, there is the need to conduct a survey that will provide a checklist of non-timber resources in the study area so that forest management plans consider all relevant information. We also conducted a prioritization of the NTFPs following the method of Adeola et al.,[14] and the Use-Value index proposed by Phillips and Gentry[15]. Then we examined the relationship between the two prioritization procedures. This is with a view to determining the reliability of the different indices as substitutes to be used for the same end.

2. Materials and Methods

2.1. The Study Area

Omo Forest Reserve (OFR) is located between Latitudes 6^o 35’ - 7^o 05’N and Longitudes 4^o 19’ - 4^o 40’E in the Ijebu East and North Local Government Areas of Ogun State, southwestern Nigeria (Figure 1). The Reserve covers an area of about 130,500 hectares forming common boundaries with Osun, Ago-Owu and Shasha Forest Reserves in Osun State and Oluwa Forest Reserve in Ondo State. It also shares some common natural endowments with these forest reserves. The Nigerian Government legally gazetted it a forest through Order No. 10 Gazette No. 40 of 7th May 1925 which was amended in 1952[16]. The forest was originally ceded to Government for reservation on the 8th of October, 1918 via an agreement made between the District Officer, Ijebu Ode on behalf of the British Colonial government and the Awujale of Ijebu Ode on behalf of the Ijebu Native Administration. The government in 1946 established a 460 ha Strict Nature Reserve (SNR) within Omo Forest Reserve. This was upgraded to a Biosphere Reserve (BR) in 1977 by UNESCO[17;18].

The rainy season in OFR usually commences in March. The mean annual rainfall in the area ranges from about 1600 to 2000 mm with two annual peaks in June and September. The driest months are November and February[19]. Temperature ranges from 32.15⁰C to 21.40⁰C and a minimum relative humidity of 76.34 %[20]. The vegetation of the Reserve is a mixed moist semi-deciduous rainforest. Earlier works in Omo reported by Okali and Ola-Adams[17] distinguished a dry forest in the northern part and a humid forest in the southern part. The plant families with the most abundant individuals include Araceae, Compositae, Ebenaceae, Lilliaceae, Papilionoideae, Poaceae, Rubiaceae and Violaceae. The most common tree species are Diospyros spp., Drypetes spp., Strombosia pustulata, Rinorea dentata and Voacanga africana[21]. Most of the forests are disturbed with a substantial parts converted to monoculture plantations of Gmelina arborea in a programme assisted by loans from the World Bank and the African Development Bank to provide material for a pulp mill at Iwopin.

For effective management, the reserve was subdivided into areas or sectors called J1, J3, J4 and J6. These subdivisions were apportioned to enclave dwellers in isolated villages or camps. In addition to these settlements (which have continued to grow), large numbers of migrant farmers have moved into the reserve, some of them encouraged as taungya farmers to help create the Gmelina plantations. Within the various sectors, there are several settlements (both legal and illegal enclaves). Estimated total population in the area is between 20,000 and 25,000. Farming, fishing, hunting and NTFPs gathering are the predominant occupations for the majority of the enclaves’ population.

2.2. Data Collection and Analysis

Socio-economic survey of NTFPs was carried out in the J4 sector of the reserve. Using a simple random sampling technique, four enclaves were selected for household survey. Data were obtained on the ethnobotanical uses of NTFP species through semi-structured interview. A total of 81 households were sampled. To complement information from the household survey, focus group discussion (FGD) was also conducted in each of the sampled community. This provided forum for weighing the relative importance of identified NTFPs and opportunity for more reliable data to be generated.

The ethnobotanical data generated were subjected to descriptive statistics using frequency distribution, tables, and percentages. For the ranking and prioritization exercise, we followed the method of Adeola et al.,[14] and the Use-Value index proposed by Phillips and Gentry[15]. Using the technique of Adeola et al., each respondent was to list ten most important NTFPs derived from the forest in their order of importance. The list of NTFPs was then scored in ascending order from 1 – 10. The first most important product was scored 1 while the least was scored 10. The scores for all the respondents were pooled for all the identified NTFPs and the mean for each species calculated. Products with the least mean score was ranked highest and the trend continued in that order. To establish the final position of an NTFP species in the ranking exercise, the following parameters were calculated; i. number of times each NTFP was mentioned (a), ii. Mentioned Value (b), iii. Average Ranking (for a particular NTFP) by respondents (c), iv. Rank Value (d) and; v. Final Assigned Value (e). The number of times a particular NTFP was mentioned (a) was computed to obtain its Mentioned Value (b). Average Ranking (c) of each NTFP was calculated as a function of the sum of its assigned ranking by each respondents divided by the number of respondents. The Rank Value (d) was obtained by the tabulation and ordering of the position of the individual NTFP. Assigned Value (e) was determined by adding up Mentioned Value and the Rank Value and thereafter dividing the result by 2 i.e. e = b+d÷2.

The technique of Use-Value is based on the number of uses and the number of people that cite a given plant, indicating the species that are considered most important by a given population. We used the formula, UV = ∑U_i/n[22] to calculate the Use-value. Where: U_i = the number of uses mentioned by each informant for a given species, n = the total number of informants. For instance, if a species has 6 uses as mentioned by respondent A and the same species has 8 uses as mentioned by respondent B, then the Use-Value (UV) of that species would be: number of uses for the species divided by total number of respondents/informants citing the species (6+8/2). In this case, we have the UV as 7. Thus, the Use-Value of a given plant is determined by the number of uses locally attributed to it in relation to the number of informants.

We examined the correspondence between the above- stated techniques. To test for relationship between the values obtained for each of the two indices, the Spearman correlation coefficient was employed using the Statistical Package for Social Sciences (SPSS v. 15.0) software.

Figure 1. Map of Omo Forest Reserve Showing Sampled Communities

Table 1. Checklist of NTFPs in J4 Sector of Omo Forest Reserve S/N Family Species Local Name Habit Use(s) Part(s)used 1 Alliaceae Allium sativum, L. Ayuu (Garlic) Creeper Medicine Fruit 2 Anacardiaceae Spondias mombin L. Iyeye Tree Medicine, Snacks Fruit, Leaf 3 Annonacae Monodora myristica (Gaertn) Dunal. Ariwo Tree Medicine Seed, Bark 4 Annickia (syn. Enantia) chlorantha (Oliv.) Setten & Maas Awopa (Yaani) Tree Medicine Bark 5 Apocynaceae Rauvolfia vomitoria Afzel. Asofeyeje Tree Medicine Leaf 6 Alstonia boonei De Wild. Awun Tree Medicine Bark 7 Hunteria umbellata (K. Schum) Eerin Tree Medicine Fruit 8 Picralima nitida (Stapf) Th. & H. Dur Erin Tree Medicine Seed, Bark 9 Asclepiadaceae Mondia whitei (Hook.f.) Skeels Isigun Herb Soup Root 10 Gongronema latifolium Benth. Iteji Shrub or Tree Soup Leaf 11 Parquetina nigrescens (Afzel.) Bullock Ogbo Twine Medicine Leaf 12 Asteraceae Crassocephalum crepidioides (Benth.) S. Moore Ebolo Herb Soup Leaf 13 Ageratum conyzoides, L. Imi esu Herb Medicine Leaf 14 Erigeron floribundus (Kunth) Sch.Bip. Olowojeja Herb Medicine Leaf 15 Bignoniaceae Newbouldia laevis (P. Beauv.) Seem. ex Bureau Akoko Tree or Shrub Medicine, Traditional rite Leaf 16 Kigelia africana (Lam.) Benth. Pandoro Tree Medicine Fruit 17 Boraginaceae Cordia millenii, Baker Omo Tree Medicine Bark 18 Caesalpiniaceae Gossweilerodendron balsamiferum (Verm.) Harms Agba Tree Medicine Bark 19 Brachystegia eurycoma Harms, B. Akporachi (EKU) Tree Soup Seed 20 Afzelia Africana Sm. Apa Tree Soup, Fodder Seed, Leaf 21 Dialium guineense Willd. Omoyin Tree Sweets Fruit 22 Capparaceae Buchholzia coriacea Engl. Kokoroijemu/Obiikoro Tree Medicine Seed 23 Celastraceae Hippocratea indica Willd. Mawole Climbing shrub Medicine Root 24 Chrysobalanaceae Parinari excelsa Sabine Abere Tree Medicine, Traditional rites Fruit, Bark 25 Clusiaceae Garcinia kola, Heckel. Orogbo Tree Snacks Seed 26 Combretaceae Terminalia ivorensis A. Chev. Afara dudu Tree Medicine Bark 27 Connaraceae Cnestis ferruginea, DC Gboyin-gboyin Tree Medicine Leaf 28 Cucurbitaceae Momordica foetida Schumach. Ejinrin Herb Medicine Leaf 29 Momordica angusticephalas, Harms Kainkan Climber Washing Fruit 30 Dichapetalaceae Dichapetalum pallidum Marigbo Tree Soup Leaf 31 Euphorbiaceae Euphorbia hirta L Tomide Herb Fodder Leaf 32 Tetracarpidium conophorum (Mull.Arg.) Hutch.& Dalziel Asala Climbing shrub or Liana Snacks Fruit 33 Fabaceae Erythrina senegalensis D.C Ilaka ile Tree Soup Leaf 34 Abrus precatorius, L. Ojuologbo Tree Medicine Seed 35 Irvingiaceae Irvingia gabonensis (Aubry-Lecomte ex O'Rorke) Baill Aapon (Ogbono) Tree Soup Seed 36 Irvingia wombulu Ooro Tree Snacks Fruit 37 Labiatae Ocimum basilicum L. Igi ota Shrub Medicine, Chew-stick Stem, Branch 38 Lamiaceae Culcasia saxatilis, A.Chev. Agunmona Herb Medicine Fruit 39 Lauraceae Beilschimiedia mannii, (Meisn.) Benth. & Hook. f Gbokoniga Tree Soup Leaf 40 Malvaceae Ceiba pentandra, (L.) Gaertn. Eegun Tree Medicine, Soup Leaf 41 Sida veronicifolia, Lam. Esi-ile Creeper Sweet Fruit 42 Malvaceae- Sterculoidae Cola acuminata Schott & Endl. Obi Abalaye Tree Traditional rites Fruit 43 Marantaceae Thaumatococcus daniellii (Benn.) Benth. Ewe eeran Herb Packaging leaves Leaf 44 Meliaceae Trichilia rubescens, Oliv Kurere Tree Medicine Stem, Branch 45 Khaya ivorensis A. Chev. Oganwo Tree Medicine Bark 46 Menispermaceae Cissampelos owariensis, P. Beau Jenjoko Climber Medicine, Soup Leaf, Bark 47 Mimosaceae Piptadeniastrum africanum, (Hook.f.) Brenan Agboin Tree Medicine Root 48 Tetrapleura tetraptera (Schumach. & Thonn.) Taub. Aidan Tree Medicine Fruit 49 Moraceae Treculia africana Decne. Afon Tree Medicine, Food, Snacks Fruit, Seed 50 Musanga cecropioides R.Br. Aga Tree Medicine Stem, Branch 51 Artocarpus altilis (Parkinson) Fosberg Berefuutu Tree Food Fruit 52 Ficus exasperata Vahl Ipin Tree Medicine Leaf 53 Nyctaginaceae Boerhavia diffusa, L. Etiponnla Herb Soup Leaf 54 Ochnaceae Lophira alata Banks ex Gaertn. Pahan Tree Medicine Bark 55 Palmae Raphia hookeri G.Mann & H.Wendl. Ako (Raffia palm) Palm Beverage, Construction Stem, Leaf 56 Phytolaccacea Pativera alliaceae, L. Awogba Herb Medicine Leaf 57 Piperaceae Piper guineense Schumach. & Thonn. Iyere Liana Spices Seed, Leaf 58 PoaceaePoaceae Chloris pilosa Schumach. Eeran Grass Medicine Leaf 59 Bambusa vulgaris Schrad. Oparun Grass Construction Stem, Leaf 60 Polygalaceae Carpolobia lutea G. Don Osunsun/Sanda Shrub Animal care Stem 61 Rubiaceae Mitragyna ciliata, Aubrév. & Pellegr Abura Tree Medicine, Packaging Leaf, Bark 62 Nauclea diderrichii (De Wild. & T.Durand) Merrill Opepe Shrub Medicine Leaf 63 Gardenia erubescens, Stapf & Hutch. Orunwo Shrub or Tree Medicine Leaf 64 Morinda lucida Benth. Oruwo Tree Medicine, Construction Leaf, Bark 65 Massularia acuminata (G Don) Bullock Pako Shrub or Tree Chew-stick Stem, Branch 66 Ruscaceae-Agavaceae Sansevieria trifasciata, Prain. Oja ikoko Creeper Medicine Leaf 67 Rutaceae Zanthoxylum zanthoxyloides, (Lam.) Zepern. & Timler Igi ata Shrub Spices Leaf, Root, Bark 68 Sapindaceae Blighia sapida, K.D.Koenig Isin Tree Medicine, Snacks Fruit, Leaf, Bark 69 Sapotaceae Chrysophylum albidum, G. Don Agbalumo Tree Snacks Fruit 70 Synsepalum dulcificum (Schumach. & Thonn.) Daniell Agbayun Shrub Snacks Fruit 71 Solanaceae Capsicum spp. Ata ijosi Shrub Spices Fruit 72 Varies Edible mushrooms Ataase (Olu) Fungi Food supplement Whole fungus 73 Zingiberaceae Aframomum sceptrum (Oliv. & Hanb.) K Schum. Ata oguro Herb Spices Fruit, Seed 74 Aframomum melegueta K. Schum. Ataare Herb Medicine Fruit, Seed 75 Zingiber officinale, Roscoe Ata-ile (Ginger) Tuber Spices Root

Table 2. Ranking and prioritization of NTFPs in J4 Omo Forest Reserve S/N Species Local Name Number of times Mentioned Mentioned Value Average Rank Rank Value Assigned Value (Adeola et al., 1994) Use-Value (Phillip and Gentry, 1993) 1 Irvingia gabonensis Aapon (Ogbono) 18 8 2.3 9 8.5 0.03 2 Tetracarpidium conophorum Asala 39 4 3.8 13 8.5 0.06 3 Massularia acuminata Pako 33 6 3.7 12 9 0.03 4 Anninckia chloranta Awopa/Yaani 51 1 4.2 18 9.5 0.06 5 Piper guineense Iyere 42 3 4.3 20 11.5 0.05 6 Bucholzia coriaceae Kokoroijemu/Obiikoro (wonderful kola) 48 2 4.5 22 12 0.02 7 Edible mushrooms Ataase (Olu) 18 8 4.8 25 13 0.02 8 Irvingia wombulu. Ooro 15 15 3.3 11 13 0.07 9 Hippocrata indica. Mawole 6 31 1.5 2 16.5 0.17 10 Aframomum melegueta Ataare 6 31 2 3 17 0.17 11 Treculia africana Afon 6 31 2 3 17 0.50 12 Zanthoxylum zanthoxyloides Igi ata 6 31 2 3 17 0.33 13 Tetrapleura tetraptera Aidan 9 20 4 14 17 0.11 14 Artocarpus artilis Berefuutu 9 20 4 14 17 0.11 15 Momordica foetida Ejinrin 12 17 4.5 22 19.5 0.08 16 Chrysophylum albidum Agbalumo 9 20 4.3 20 20 0.11 17 Garcinia kola Orogbo 36 5 5.3 35 20 0.03 18 Thaumatoccocus daniellii Ewe eeran 6 31 3 10 20.5 0.17 19 Synsephalum dulcificum Agbayun 12 17 4.8 25 21.0 0.08 20 Beilschimiedia mannii Gbokoniga 18 8 5.5 36 22 0.06 21 Parinari excelsa. Abere 9 20 5 26 23 0.17 22 Chloris pilosa Eeran 18 8 5.8 38 23 0.11 23 Cola acuminate Obi Abalaye 18 8 5.8 38 23 0.06 24 Monodora myristica Ariwo 6 31 4.1 16 23.5 0.17 25 Bambusa vulgaris Oparun 15 15 5.2 34 24.5 0.07 26 Allium sativum Ayuu (Garlic) 3 50 1 1 25.5 0.33 27 Mitragyna ciliata Abura 24 7 6.9 45 26 0.08 28 Crassocephalum crepidioides Ebolo 3 50 2 3 26.5 0.33 29 Gardenia erubescens Orunwo 3 50 2 3 26.5 0.33 30 Blighia sapida Isin 3 50 2 3 26.5 1.00 31 Brachystegia spp. Akporachi (EKU) 6 31 4.5 22 26.5 0.17 32 Aframomum sceptrum Ata oguro 6 31 5 26 28.5 0.17 33 Momordica angusticephalas Kainkan 9 20 5.7 37 28.5 0.11 34 Erythrina senegalensis Ilaka ile 9 20 6 40 30 0.11 35 Alstonia boonei Awun 18 8 7.3 54 31 0.06 36 Cissampelos owariensis Jenjoko 3 50 4.1 16 33 0.33 37 Raffia hookeri Ako (Raffia palm) 9 20 7 46 33 0.22 38 Trichilia rubescens Kurere 6 31 5.5 36 33.5 0.17 39 Nauclea diderichii Opepe 3 50 4.2 18 34 0.33 40 Piptedeniastrum africanum Agboin 18 8 8 60 34 0.06 41 Spondis mombin Iyeye 18 8 8 60 34 0.06 42 Ceiba pentadra Eegun 12 17 7.5 56 36.5 0.08 43 Khaya ivorensis Oganwo 9 20 7.3 54 37 0.11 44 Picralima nitida Erin 3 50 5 26 38 0.33 45 Capsicum spp Ata ijosi 3 50 5 26 38 0.33 46 Sida veronicifolia Esi-ile 3 50 5 26 38 0.33 47 Ocimum basilicum Igi ota 3 50 5 26 38 0.67 48 Carpolobia lutea. Osunsun/Sanda 3 50 5 26 38 0.33 49 Afzelia Africana Apa 6 31 7 46 38.5 0.33 50 Dialium guineense Omoyin 6 31 7 46 38.5 0.17 51 Morinda lucida Oruwo 9 20 7.7 59 39.5 0.11 52 Parquetina nigrescen Ogbo 9 20 8.3 66 43 0.11 53 Abrus precatorius Ojuologbo 6 31 7.5 56 43.5 0.17 54 Musanga cecropioides Aga 3 50 6 40 45 0.33 55 Zingiber officinale Ata-ile (Ginger) 3 50 6 40 45 0.33 56 Gossweilerodendron balsamiferum Agba 3 50 6 40 45 0.33 57 Cnetis ferruginea Gboyin-gboyin 3 50 6 40 45 0.33 58 Newbouldia laevis Akoko 6 31 8 60 45.5 0.17 59 Culcasia saxatilis Agunmona 6 31 8 60 45.5 0.17 60 Mondia whitei Isigun 6 31 8 60 45.5 0.17 61 Gongronema latifolium Iteji 9 20 9.3 72 46 0.22 62 Terminalia ivorensis Afara dudu 3 50 7 46 48 0.33 63 Hunteria umbellata Eerin 3 50 7 46 48 0.33 64 Cordia millenii Omo 3 50 7 46 48 0.33 65 Ficus exasperata Ipin 3 50 7 46 48 0.33 66 Pativera alliaceae Awogba 3 50 7 46 48 0.33 67 Ageratum conyzoides Imi esu 6 31 8.5 67 49 0.17 68 Lophira alata Pahan 6 31 8.5 67 49 0.17 69 Dichapetalum pallidum Marigbo 6 31 10 73 52 0.17 70 Boerhavia diffusa Etiponnla 3 50 8 60 55 0.33 71 Sansevieria trifasciata Oja ikoko 3 50 8 60 55 0.33 72 Erigeron floribundus Olowojeja 3 50 8 60 55 0.33 73 Kigelia africana Pandoro 3 50 9 69 69.5 0.33 74 Rauvolfia vomitoria Asofeyeje 3 50 10 73 69.5 0.33 75 Euphorbia hirta. Tomide 3 50 10 73 69.5 0.33

3. Results

3.1. Checklist of NTFPs

Respondents mentioned a total of seventy five non-timber forest product species distributed in forty three families in the study area (Table 1). The dominants families were Rubiaceae, Apocynaceae, Asclepiadaceae, Asteraceae, Caesalpiniaceae and Zingiberaceae. Products were extracted from trees, shrubs, herbs, fungi and lianas. Local end-uses include food and food supplements, snacks/sweets, soup/soup ingredients/spices, beverages (consumptive plants), packaging leaves, chew-sticks, washing items, construction materials, medicine, traditional rites, and animal feed and care. The most frequently mentioned uses of plants were medicine (n=42; 50.00%), consumptive (n=30; 35.71%), house construction (n=3; 3.57%), traditional rites (n=3; 3.57%) and animal feed and care (n=3; 3.57%). Other uses of listed NTFPs include use as chew-stick (n=2; 2.38%), packaging leaves (n=2; 2.38%), and item for washing and bathing (n=1; 1.19%) (Figure 2).

Figure 2. Uses of NTFPs and Frequency in Sampled Communities

3.2. Ranking and Prioritization of NTFPs

Using the Assigned-Value method developed by Adeola et al.,[14] and described in the data analysis section, Apon (Irvingia gabonensis), Asala (Tetracarpidium conophorum), Pako (Masssularia acuminata), Awopa/Yaani (Annickia chloranta) and Iyere (Piper guineense) ranked as the five top priority species (Table 2). Applying the Use-Value index; Isin (Blighia sapida), Igi ota (Ocimum basilicum), Afon (Treculia africana), Igi ata (Zanthoxylum zanthoxyloides) and Ayuu (Allium sativum) were the five top priority species. Conversely, on the Use-Value index Apon ranked 71st, Asala 63rd, Pako 72nd, Awopa/Yaani 64th and Iyere 70th. On the other hand, Isin (Blighia sapida) ranked 30th, Igi ota (Ocimum basilicum) 47th, Afon (Treculia africana) 11th, Igi ata (Zanthoxylum zanthoxyloides) 12th and Ayuu (Allium sativum) 26th when applying the Assigned-Value method. A general comparison of the two indices shows a fairly positive correlation (ρ = 0.59; P< 0.01) between them. When the correlations were further analyzed considering the values obtained for each technique versus the number of times a given species was mentioned, there was a strong negative correlation for the two, being greater for the Use-Value technique (ρ = -0.95; P< 0.01) than Assigned-Value method (ρ = -0.65; P< 0.01). In other words, there is a general inverse relationship between the number of times a given species was mentioned and its value/ranking in both techniques.

4. Discussion

The results of the two quantitative techniques have shown a fairly positive correlation (ρ = 0.59; P< 0.01) between the two, suggesting a cautious interchangeable use of the techniques for the same end. According to Philips et al.,[23], the Use-Value reflects the importance of a species to the respondent objectively. However, Use-Value places more emphasis on species that have many uses, even if these uses are only known to a few people[22; 24]. The number of uses is therefore the principal factor in this technique. Nonetheless, the technique may indicate how knowledge about a certain plant is distributed in a community[24]. Our findings suggest that the Use-Value, more often than not, gives a higher ranking to species that are more widely used for subsistence or consumptive value. This is contrary to the submission of Philips et al.,[23] that Use-Value could be used simultaneously for evaluating species with direct subsistence and commercial value. On the other hand, however, the Assigned-Value gives priority to species that have more commercial value being the major consideration of its inventors. The importance of a plant may therefore, not derives from the different ways it is used. Conversely, the local importance of NTFPs would need to take into account various combinations of objectives such as the species role in subsistence, commercial and socio-cultural activities. While Albuquerque et al.,[22] have rejected the association of the Use-Value with questions of conservation (i.e. the most important species will suffer the greatest harvesting pressure), the Assigned-Value may support the view that species with high commercial value often face increased exploitation. From the foregoing, it seems both the Use-Value and the Assigned-Value does not capture the same aspect of traditional ecological knowledge of a species. Thus, in evaluating forest types for relative importance and use, the end objectives of such evaluation must be critically examined in the light of the interest of the different respondents’ group.

5. Conclusions

The use of quantitative techniques has received increasing attention in ethnobotanical studies. Identifying NTFP species with the potential for sustainable and profitable extraction in a managed system may however, not lend easily to quantitative approaches found in the ethnobotanical literatures. Quantitative techniques used in Ethnobotany often reflect cultural value systems than conservation concern or priority of species for socio-economic development. Therefore, determining NTFPs with top priority concern will require the development of criteria for species selection such as economic importance, level of use, species habit and population status. Unlike the setting of approach by experts in ethnobotanical studies, thus, determining the local importance of NTFPs must necessarily be based on participatory resource appraisal.

ACKNOWLEDGEMENTs

We express our sincere gratitude to village leaders and communities in the project area for providing the enabling environment to carry out the survey. We deeply appreciate the assistance in logistics and personnel provided by the management authorities of Omo forest reserve, Ogun State, Southwest Nigeria.