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Agroforest Syst (2012) 86:493–504 DOI 10.1007/s10457-012-9513-9

Afforestation of savannah with cocoa agroforestry systems: a small-farmer innovation in central

Patrick Jagoret • Isabelle Michel-Dounias • Didier Snoeck • Herve´ Todem Ngnogue´ • Eric Male´zieux

Received: 14 July 2011 / Accepted: 17 March 2012 / Published online: 4 April 2012 Ó Springer Science+Business Media B.V. 2012

Abstract Cocoa cultivation is generally considered grasslands and 182 cocoa plantations established in to foster deforestation. Contrary to this view, in the gallery . In a sub-sample of 47 grassland cocoa –savannah interface area in Cameroon, farmers plantations, we inventoried species associated have planted cocoa agroforestry systems on Imperata with cocoa and measured soil organic matter cylindrica grasslands, a soil-climate zone generally levels. Marketable cocoa yields were similar for the considered unsuitable for cocoa cultivation. We two types of cocoa plantations, regardless of their age: undertook a survey to understand the agricultural 321 kg ha-1 in cocoa plantations on grasslands and and ecological bases of this innovation. Age, cropping 354 kg ha-1 in cocoa plantations in gallery forests. history and marketable cocoa yield were assessed in a Two strategies were used by farmers to eliminate sample of 157 cocoa plantations established on I. cylindrica prior to the establishment of cocoa plantations, i.e., cropping oil palms in dense stands and planting annual crops. Farmers then planted cocoa trees and species, while preserving specific forest trees. The fruit tree and forest tree densities -1 P. Jagoret (&) Á D. Snoeck respectively averaged 223 and 68 trees ha in CIRAD, UPR Syste`mes de Pe´rennes, 34398 Montpellier plantations under 10 years old, and 44 and 27 cedex 5, France trees ha-1 in plantations over 40 years old, whereas e-mail: [email protected] the cocoa tree density remained stable at 1,315 -1 P. Jagoret Á H. T. Ngnogue´ trees ha . The Shannon–Weaver index increased Perennial Crop Department, IRAD-Nkolbisson, BP 2067, from 1.97 to 2.26 over the same period although the Yaounde´, Cameroon difference was not statistically significant. The soil I. Michel-Dounias organic matter level was 3.13 % in old cocoa planta- UMR 951 Innovation Montpellier Supagro INRA CIRAD, tions, as compared to 1.7 % in grasslands. In conclu- Campus de la Gaillarde, 2 Place Viala, 34060 Montpellier sion, our results show that the occupation of grasslands cedex 1, France by cocoa agroforestry systems is both an important I. Michel-Dounias Á E. Male´zieux example of ecological intensification and a significant CIRAD, UPR HortSys, 34398 Montpellier cedex 5, farmer innovation in the history of cocoa growing. France Keywords Imperata cylindrica Á Sustainability I. Michel-Dounias Institut des Re´gions Chaudes, 1101 Avenue Agropolis, BP assessment Á Agrobiodiversity Á Ecological 5098, 34093 Montpellier Cedex 05, France intensification Á Forest–savannah interface 123 494 Agroforest Syst (2012) 86:493–504

Introduction matter levels. According to Burle (1961), cocoa trees require 1,500–2,500 mm of water a year, with a dry In Africa, cocoa ( L.) cultivation is season that has less than three consecutive months of generally considered to be a major cause of defores- below 70 mm. Sandy-clayey soils with over 3 % tation in humid tropical areas since the trees are often organic matter in the topsoil are the most suitable soils planted on newly cleared forest land (Dixon et al. for cocoa growing. However, such conditions do not 2001). The expansion of cocoa plantations in Coˆte prevail in the forest–savannah interface area in central d’Ivoire, for instance, led to a reduction in the Cameroon where the annual average rainfall is around country’s forest area from 13 million ha in 1960 to 3 1,300 mm with sandy topsoil which contains less than million ha in 1990 (Hanak-Freud et al. 2000). The 2 % organic matter (Santoir and Bopda 1995). same pattern has been noted in , where it is Champaud (1966) also demonstrated that this area is estimated that 80 % of the forest area has disappeared far north of the boundary of the ideal cocoa growing since cocoa trees were introduced (Cleaver 1992). region in this country. Planting cocoa agroforestry In Cameroon, the role of cocoa cultivation in the systems on I. cylindrica grasslands in central Camer- deforestation process is not as clear since forests oon thus seems to contradict the opinion of cocoa are generally only partially cleared for planting cocoa, experts. many forest tree species being preserved in Vieira et al. (2009), in their review article on the resulting complex cocoa agroforestry systems the concepts of agroforestry systems and agro- (Duguma et al. 2001; Zapfack et al. 2002; Laird et al. successional restoration, highlighted the shortage of 2007; Sonwa et al. 2007). scientific literature on the description and analysis of In the present study, we show that cocoa growing agro-successional restoration examples in the world, contributes to the process of afforestation of grass- especially in tropical areas. These authors also stated lands dominated by Imperata cylindrica in the forest– that both scientists and farmers involved in agrofor- savannah transition area of central Cameroon. Pub- estry should think about how agroforestry and resto- lished reports about afforestation in forest–savannah ration might be integrated in different situations. In interface areas in Africa are relatively ancient. In most central Cameroon, grassland cocoa agroforestry sys- situations, this process was due to the natural dissem- tems are an as yet undocumented example of this. ination of forest tree species, as described by Boulvert The objective of the present study was to document (1990) in the , Clayton the gradual transformation of grasslands into cocoa (1958) in , Swaine et al. (1976) in Ghana, agroforestry systems in the forest–savannah interface and Bonvallot et al. (1970) and Spichiger and Pamard area of central Cameroon. Firstly, we checked the age (1973)inCoˆte d’Ivoire. Only a few cases of voluntary of the cocoa plantations established on grasslands and afforestation have been described in (Guelly we compared their cocoa yields to those of cocoa et al. 1993), Coˆte d’Ivoire (Blanc-Pamard and Peltre plantations in gallery forests. Secondly, we focused on 1984) and (Fairhead and Leach 1996), where the conditions required for establishing cocoa agro- Robusta coffee-based agroforestry systems were forestry systems on grasslands and farmers’ manage- planted, since this coffee cultivar is able to adapt to ment of the different associated stands of tree species. grassland soil and microclimatic conditions. Finally, we assessed the agrobiodiversity and soil To our knowledge, only one case of afforestation fertility in these systems using the Shannon–Weaver involving cocoa trees has been reported in Indonesia index and the total soil carbon content respectively. (Ruf and Yoddang 2004), where farmers in central Sulawesi planted cocoa trees on I. cylindrica grass- lands after conducting chemical weed control sprays Materials and methods and planting the leguminous tree Gliricidia sepium to eliminate the grass and temporarily shade the young Study site cocoa trees. According to and Lass (1985), grassland areas are theoretically unable to fulfil the The study was carried out in the forest–savannah ecological requirements of cocoa trees because of the interface area in central Cameroon, around the villages insufficient and variable rainfall and low soil organic of Bakoa, Begni, Yorro and Kedia in Bokito district: 123 Agroforest Syst (2012) 86:493–504 495

4°30 latitude N and 11°10 longitude E; 450–500 m rainfall conditions would normally induce defoliation, elevation (Fig. 1). The farmers were mainly indige- which could be fatal to the trees (Burle 1961). Ferric nous ethnic Yambassa people. Bokito district Acrisols predominate in this area. The topsoil contains (7,125 km2) is a patchwork of gallery forests occu- over 60 % sand and less than 2 % organic matter pied by cocoa agroforestry systems and grasslands (Santoir and Bopda 1995), which are further con- dominated by I. cylindrica. Invasion of fields by straints for cocoa trees (Burle 1961). I. cylindrica is a major farming constraint because this heliophytic weed quickly reappears as soon as the crop Experimental design, stakeholder survey data fields are insufficiently maintained or when the crop and measured data cover is sparse (Deuse and Lavabre 1979). The forest–savannah interface area has a hot and In 2004, 339 cocoa plantations belonging to 282 humid climate with an average annual temperature of farmers were randomly selected from lists of farmers 25 °C. Mean annual rainfall is 1,300 mm, which belonging to local cocoa growers’ organizations. We represents a mean deficit of 200 mm relative to the interviewed each of these farmers to collect the minimal annual water needs of cocoa trees. The following data: year of establishment of each cocoa rainfall distribution is characterized by a dry season plantation (plantation age in years), vegetation cover lasting over 3 months (December–March) during before cocoa trees were planted (gallery forest or which the monthly rainfall is less than 70 mm (Santoir grassland), area and declared production for the three and Bopda 1995). In monocropped cocoa stands, these harvest seasons prior to the survey (2001, 2002, and

300 R (mm) 250 200 NORTH 150 100 Chad Nigeria 50 0 JFMAMJJASOND Central Bokito African Republic

Yaoundé

Atlantic Ocean

Bakoa Equatorial Congo Kedia Guinea Begni Yorro State capital Regional borders Main road Study site

Yaoundé Forest Savanna Study village

Fig. 1 Map showing the location of the study sites in central Cameroon 123 496 Agroforest Syst (2012) 86:493–504

2003). The mean marketable cocoa yield of each cocoa variance (ANOVA) using a general linear model. plantation was calculated on the basis of the reported Tests of significance between age categories of cocoa area and production data. Data were analysed according agroforests were performed using the Fisher test. to seven cocoa plantation age (since creation) catego- When significant differences were observed, the ries, which were defined in decades so as to be in line Newman–Keuls test was used to compare means with the cocoa tree biological cycle: immature cocoa between treatments. plantations under 10 years old; mature cocoa planta- tions: 11–20 years, 21–30 years, 31–40 years; senes- cent cocoa plantations: 41–50 years, 51–60 years, Results 61 years and over. We also interviewed village heads and elders about the different steps in the history of Age and yields of cocoa agroforestry systems cocoa growing in the region. on grasslands A sub-sample of 47 grassland cocoa plantations was then randomly selected. In each of these cocoa Out of the 339 cocoa plantations sampled, 46.3 % plantations, the cocoa stand density was measured by (157 plantations) had been established on grasslands, counting cocoa in a randomly located while the rest were in gallery forests (182 plantations). 10 m 9 10 m (100 m2) sample plot. All non-cocoa Cocoa cultivation on grasslands appears to be a long- trees exceeding 1 m in height were inventoried over standing ongoing practice (Fig. 2): in the sample the total area of each cocoa plantation. We identified surveyed, the oldest cocoa plantations on grasslands forest tree species, fruit tree species (exotic and had been reportedly planted in the first half of the indigenous) and oil palms. The species identifications twentieth century. According to the village heads and were based on vernacular names in the Yambassa elders, cocoa growing had spread to grassland areas up language and correspondences with the scientific until 1950 because gallery forests were traditionally names were established from the tree identification off limits for development, i.e., they were preserved as manuals of Vivien and Faure (1985) and Wilks and refuge areas during tribal wars. As of the 1950s, cocoa Issembe´ (2000). The agrobiodiversity level was esti- growing began in gallery forests since it was no longer mated according to the Shannon–Weaver index (Krebs prohibited and based on recommendations by 1985). We asked each farmer to specify the origin of the inventoried trees, i.e., those that had grown naturally and had been preserved by the farmers and those they had introduced. We also asked farmers about the way they managed stands of cocoa and other associated species over time. A composite soil sample was collected in the topsoil (0–20 cm) in each of the 47 grassland cocoa plantations and in 10 adjacent grassland plots to assess clay (AFNOR 2003) and carbon contents (Walkley and Black 1934). Agrobiodiversity level, soil clay and carbon con- tents were analysed for three main stages of cocoa tree development: (i) cocoa plantations less than 10 years old (17 plots totalling more than 6.5 ha), (ii) mature cocoa plantations 10–40 years old (17 plots totalling more than 11.7 ha), (iii) old cocoa plantations over 40 years old (13 plots totalling more than 17.2 ha). Fig. 2 Distribution of cocoa plantations in the forest–savannah Statistical analysis interface area in central Cameroon by age classes and original vegetation: 182 cocoa agroforestry systems in forests, 157 cocoa agroforestry systems in grasslands (2004). Cocoa cultivation on Age, density, yield, Shannon–Weaver index, and soil grassland appeared to be a long-standing ongoing practice in the carbon concentration were subjected to an analysis of forest–savannah interface area in central Cameroon 123 Agroforest Syst (2012) 86:493–504 497 extension services to clear forest plots for cocoa generates a dense cover within 4–5 years. I. cylindrica growing. Since 1980, the reduction in the available is then totally eliminated and farmers subsequently gallery forest area led to new extensions on grasslands. reduce the oil palm density to 50 palms ha-1. During Cocoa plantations under 10 years old are now more this felling operation, they cocoa trees at a common in grasslands than in gallery forests. density of 1,500 plants ha-1, either by direct seeding The marketable cocoa yield of grassland cocoa in holes or by transplanting nursery plants. Fruit trees plantations was similar to that of cocoa plantations in such as orange (Citrus sinensis L.), African plum gallery forest, regardless of the plantation age (Fig. 3). (Dacryodes edulis (G Don) H.J. Lam), avocado After 20 years of age, cocoa yields level off at a mean (Persea americana Mill.) and cola (Cola nitida Vent.) of 321 kg ha-1 for cocoa plantations in grasslands. are also planted alongside the cocoa trees for their production. The farmers also preserve some native Strategies for setting up grassland cocoa forest tree species that have grown naturally in the agroforestry systems plots, such as Ceiba pentandra L., Erythrophleum ivorense A. Chev. and Milicia excelsa Berg, for shade I. cylindrica is a major constraint for all crops due to but also for their economic and fertilising potential. competition for water and nutrients. It is therefore For 2–3 years following cocoa planting, the plot is still essential to control this weed before establishing weeded manually until the crowns of cocoa trees and grassland cocoa plantations. Two different strategies associated trees form a continuous dense canopy that for eliminating I. cylindrica prior to cocoa planting will hamper natural regrowth of I. cylindrica. were identified: the first consists of sowing oil palm I. cylindrica can be controlled quicker (within (Elaeis guineensis Jacq.) trees in high-density stands, 4–6 years) using the second strategy. Farmers manu- while the second consists of growing annual crops ally deep-till the plot and uproot the I. cylindrica (Fig. 4). plants to activate the weed control process. Then With the first strategy, I. cylindrica is cleared from farmers successively sow short-cycle annual crops, the plot within 6–8 years. The fast growth of the oil including groundnut (Arachis hypogaea L.), pumpkin palm planted at high density (1,200 plants ha-1) (Cucumis mani L.) and maize (Zea mays L.). After 2–3 years of intercrop successions such as groundnut– maize and pumpkin–maize, farmers plant cocoa at a density of 1,500 plants ha-1, either by transplanting seedlings or by direct seeding when the previous annual crops are being uprooted. As for the first strategy, fruit trees and oil palms are planted along with the cocoa trees and some naturally growing forest trees are preserved. The young trees are associated with annual crops for another 2–3 years. The plots are weeded to control I. cylindrica regrowth until the tree canopy is closed.

Agrobiodiversity and stand management

4,846 trees associated with cocoa trees and belonging to 67 different species were inventoried in the 47 grassland cocoa plantations (Table 1). Fruit trees Fig. 3 Marketable cocoa yields of cocoa plantations in the represented 47.7 % of the total tree population, oil forest–savannah interface area in central Cameroon by age palms 28.6 % and forest trees 23.7 %. Ten of the fruit classes and original vegetation (mean for 2001, 2002, and 2003). tree species were exotic and seven were indigenous. The marketable cocoa yield of grassland cocoa plantations was similar to that of gallery forest cocoa plantations, regardless of The cocoa trees and oil palm densities did not vary the plantation age with the cocoa plantation age, i.e., a mean of 1,315 123 498 Agroforest Syst (2012) 86:493–504

Yr 40

Cocoa trees Oil palms Redensification / continuous Forest trees replacement of cocoa trees Fuit trees and oil palms Annual crops Reduction of Imperata associated tree grassland density 010 Yr 10 Scale : meters Introduction/ preservation of natural forest trees Plantation Plantation of of fruit Yr 3 fruit trees and trees Plantation of oil palm trees Reduction of cocoa trees Yr 0 oil palms Tilling and sowing density of annual crops Yr -2 Sowing of oil palms at high density Yr -5

S1 Time S2

Fig. 4 Temporal change in grassland cocoa agroforestry proportion of different types of trees/oil palms associated with systems according to the I. cylindrica control strategy in central cocoa trees changed with time, and a balance was gradually Cameroon: (S1) previous installation of high density oil palm reached in the old grassland cocoa plantations stands; (S2) several successions of short-cycle annual crops. The

cocoa trees and 48 oil palms per hectare (Table 2). The stands to hamper rapid weed invasion and to obtain associated fruit and forest tree species densities were suitable shading conditions for the cocoa trees. Young lower in old and mature cocoa plantations whereas forest trees could also be transplanted in the plots if they were significantly higher in the youngest cocoa farmers estimated that there were not enough of them plantations. The proportion of different types of trees/ growing naturally. 25 % of the forest trees inventoried oil palms associated with cocoa trees thus changed were thus the result of transplantation of plantlets with time, and a balance was gradually reached in the picked up in nearby gallery forests. The farmers then old cocoa plantations (Table 2). The Shannon–Wea- maintained shading conditions suitable for cocoa tree ver index of tree species associated with cocoa trees growth while compensating for the growth of associ- was 2.09 on average (Table 2). No significant differ- ated trees by eliminating excess trees—they ring- ence between cocoa plantation age classes was noted, barked these trees so that they would wilt gradually, but this index tended to increase with the cocoa thus avoiding damage to the understorey cocoa trees. plantation age. The oil palm density was stable because farmers In the surveys, farmers explained how they man- replaced felled oil palm for palm wine production. aged the different stands over time. In young cocoa Similarly, diseased or dead cocoa trees were always plantations, fruit trees were planted in high density replaced. 123 Agroforest Syst (2012) 86:493–504 499

Table 1 Tree species associated with cocoa trees (47 grassland cocoa agroforestry systems, 35.4 ha, central Cameroon) Scientific name Family Group Number % of trees

E. guineensis Jacq. Arecaceae P 1,374 28.4 C. sinensis (L.) Osbeck Rutaceae FrE 951 19.6 D. edulis (G. Don) H. J. Lam Burseraceae FrI 425 8.8 Citrus sp. Rutaceae FrE 208 4.3 P. americana Mill. Lauraceae FrE 201 4.1 C. pentandra (L.) Bombacaceae Fo 192 4.0 C. nitida (Vent.) Schott & Endl. Sterculiaceae FrI 160 3.3 Mangifera indica L. Anacardiaceae FrE 151 3.1 M. excelsa (Welw.) C. C. Berg. Moraceae Fo 129 2.7 E. ivorense A. Chev. Caesalpiniaceae Fo 125 2.6 N. laevis Seem. Ex Bureau Bignoniaceae Fo 85 1.8 Triplochiton scleroxylon K. Schum. Sterculiaceae Fo 72 1.5 F. mucoso Ficalho Moraceae Fo 55 1.1 Albizia adianthifolia (Schumach.) W. Wight Mimosaceae Fo 54 1.1 Carapa procera DC. Meliaceae Fo 54 1.1 R. heudelotii (Baill.) Pierre ex Heckel Euphorbiaceae FrI 41 \1 Citrus limon (L.) Rutaceae FrE 38 \1 Canarium schweinfurthii Engl. Burseraceae FrI 35 \1 Albizia ferruginea (Guill. & Perr.) Benth. Mimosaceae Fo 32 \1 Voacanga africana Stapf Apocynaceae FrI 32 \1 Psychotria sp. Rubiaceae Fo 29 \1 platythyrsa Baker Fo 28 \1 S. campanulata P. Beauv. Bignoniaceae Fo 25 \1 Vitex grandifolia Gu¨rke Verbenaceae Fo 25 \1 Cola millenii K. Schum. Sterculiaceae Fo 24 \1 Ficus sp. Moraceae Fo 23 \1 Citrus grandis (L.) Osbeck Rutaceae FrE 19 \1 Ficus Sur Forsk. Moraceae Fo 17 \1 Psydium guajava L. Myrtaceae FrE 17 \1 Spondias cytherea Sonn. Anacardiaceae FrE 17 \1 Allophyllus africanus P. Beauv. Sapindaceae Fo 15 \1 Sterculia tragacantha Lindl. Sterculiaceae Fo 15 \1 Irvingia gabonensis (Aubry-Lecomte ex O’Rorke) Baill. Irvingiaceae FrI 13 \1 Angylocalyx pynaertii de Wild. Papillonaceae Fo 13 \1 Musanga cecropioides R. Br. Cecropiaceae Fo 10 \1 Pseudospondias microcarpa (A. Rich.) Engl. Anacardiaceae Fo 10 \1 Afzelia pachyloba Harms Caesalpiniaceae Fo 9 \1 Fagara heitzii Aubre´v. & Pellegr. Rubiaceae Fo 7 \1 Guibourtia tessmannii (Harms) J. Le´onard Caesalpiniaceae Fo 7 \1 Hevea brasiliensis (A. de Juss.) Mu¨ll. Arg. Apocynaceae Fo 7 \1 Lannea welwitschii (Hiern) Engl. Anacardiaceae Fo 7 \1 angolensis (Welw.) Warb Fo 7 \1 Annona muricata L. Annonaceae FrE 6 \1 Ficus exasperata Vahl. Moraceae Fo 6 \1 Gambeya lacourtiana (De Wild.) Auber. & Pell. Sapotaceae Fo 6 \1 123 500 Agroforest Syst (2012) 86:493–504

Table 1 continued Scientific name Family Group Number % of trees

Tetrapleura tetraptera (Schumach. & Thonn.) Taub. Mimosaceae Fo 6 \1 Entandrophragma cylindricum (Sprague) Sprague Meliaceae Fo 5 \1 Piptadeniastrum africanum (Hook.f.) Mimosaceae Fo 5 \1 Pterocarpus soyauxii Taub. Papillonaceae Fo 5 \1 Trilepisium madagascariensis DC. Moraceae Fo 5 \1 Uapaca guineensis Mu¨ll. Arg. Euphorbiaceae Fo 5 \1 Borassus aethiopum Mart. Rutaceae Fo 4 \1 Bridelia micrantha (Hochst.) Baill. Euphorbiaceae Fo 4 \1 Cocos nucifera L. Rutaceae FrE 4 \1 Dracena arborea (Wild.) Link Agavaceae Fo 4 \1 Terminalia superba Engl. & Diels Combretaceae Fo 4 \1 Ficus vogelii Miq. Moraceae Fo 3 \1 Macaranga barteri Mull. Agr. Euphorbiaceae Fo 3 \1 Terminalia ivorensis Engl. & Diels Combretaceae Fo 3 \1 Artocarpus altilis J.R.Forst. & G.Forst. Moraceae Fo 2 \1 Baillonella toxisperma Pierre Sapotaceae Fo 2 \1 Anthocleista vogelii Planch. Loganiaceae Fo 1 \1 Dacryodes macrophylla (Oliv.) H. J. Lam. Burseraceae Fo 1 \1 Elaeophorbia drupifera (Thonn.) Stapf. Euphorbiaceae Fo 1 \1 afzelii Engl. Fo 1 \1 Heckel Clusiaceae FrI 1 \1 Tectona grandis L. Verbenaceae Fo 1 \1 Total 4,846 P palm, FrE exotic fruit tree species, FrI native fruit tree species, Fo forest tree species

Table 2 Density of cocoa trees and associated tree species (±SD of the mean) and Shannon–Weaver index according to cocoa plantation age in 47 grassland cocoa agroforestry systems in central Cameroon Age of cocoa Cocoa Oil Palm Fruit trees Forest trees Shannon–Weaver agroforestry index systems (years) Density Density %of Density %of Density %of (trees ha-1) (trees ha-1) total (trees ha-1) total (trees ha-1) total

\10 1,428 (±127)a 50 (±15)a 15 223 (±54)a 65 68 (±11)a 20 1.97 (±0.50)a 10–40 1,274 (±87)a 50 (±15)a 29 89 (±16)b 52 32 (±4)b 19 2.09 (±0.30)a [40 1,242 (±35)a 44 (±13)a 38 44 (±6)b 38 27 (±3)b 23 2.26 (±0.36)a Values within a column followed by the same letter are not significantly different (p \ 0.01, Newman–Keuls test)

Clay and soil carbon contents (3.12 %) than in plantations under 10 years old. In our surveys, farmers confirmed that they did not apply any No significant difference between cocoa plantation age type of fertilizer (organic or chemical) in their plantations. classes and the adjacent grassland plots was noted for the clay content. Ten year old cocoa plantations on grassland soils had significantly higher topsoil carbon concen- Discussion tration (2.25 %) than adjacent grassland soils (1.70 %) (Table 3). The top soil carbon concentration was signif- In central Cameroon, afforestation of grasslands by icantly higher in plantations more than 40 years old installing cocoa agroforestry systems is another 123 Agroforest Syst (2012) 86:493–504 501

Table 3 Clay and organic matter content (±SD of the mean) campanulata P., for improving the soil quality in in topsoil (0–20 cm horizon) in 10 grassland plots and in 47 infertile ecosystems. These authors also recommended grassland cocoa plantations according to their age (central these species for the rehabilitation of old cocoa Cameroon) plantations in Ghana. Age of cocoa Clay content (%) Organic matter In Cameroon, the establishment of cocoa agrofor- agroforestry systems content (%) estry systems on I. cylindrica grasslands by farmers, Grassland (control) 18.8 (±0.81)a 1.70 (±0.09)c and their efficient management of different tree stands \10 years 17.5 (±0.55)a 2.25 (±0.18)b so as to maintain shading conditions that they consid- 10–40 years 17.8 (±1.58)a 2.82 (±0.16)ab ered optimal for both controlling I. cylindrica and [40 years 19.3 (±1.61)a 3.13 (±0.37)a cocoa tree growth, showed that it is possible to overcome the presence of I. cylindrica, water deficit Values followed by the same letter are not significantly different (p \ 0.01, Newman–Keuls test) and irregular rainfall distribution, and poor soil fertility. While climatic change is one of the primary concerns for agriculture and researchers are looking example of an agro-successional strategy to restore for adaptation strategies to sustain crop productivity infertile degraded ecosystems, in line with initiatives including in Cameroon (Tingem et al. 2009), farmers’ reported in other countries (Vieira et al. 2009). A long practices to establish viable cocoa plantations on time ago, farmers in this region have developed grasslands could be also considered as a possible innovative strategies for eliminating I. cylindrica, answer to adapt cocoa cultivation to a future drier which necessarily has to be controlled before being climate in Africa. able to use grasslands for agriculture (Deuse and Without chemical or organic fertilization, the Lavabre 1979). To control I. cylindrica, these authors topsoil organic matter content, which was 1.7 % in suggested using cover plants such as Mucuna sp., the grassland plots, increased with the cocoa planta- Centrosoma sp. or Pueraria sp. or planting legumi- tion age. Our mean levels, i.e., 2.82 % in mature cocoa nous shade trees, such as the many species mentioned plantations and 3.13 % in old plantations, were in by Macdicken et al. (1997). In Indonesia, farmers agreement with the 3 % value obtained by Glatard controlled I. cylindrica by combining a herbicide et al. (2007) under cocoa plantations established on treatment and planting of G. sepium 2 years prior to grasslands in the same area. The soil organic matter planting cocoa trees (Ruf and Yoddang 2004). Farm- levels found in our cacao plantations in savanna were ers at our research site in Cameroon, in contrast, lower than those found by Duguma et al. (2001)in eliminated I. cylindrica by planting dense crop stands, mature cocoa plantations set up in forest areas in thereby generating additional revenue while preparing central and southern Cameroon (4.1–4.7 %). How- the site for the cocoa trees. ever, we did not observe the decrease in soil organic The fact that farmers preserved some natural forest carbon noted by Snoeck et al. (2010) in young cocoa tree species in grassland cocoa plantations for their plantations set up after forest clearing in the same contribution in the soil fertility status, especially areas. In grasslands, this lack of depressive effect of C. pentandra (L.), M. excelsa (Welw.) Berg., Ficus soil organic carbon, as also observed in cocoa mucoso Ficalho, Beauv., and Ricinodendron heudel- plantations installed on fallow lands, could be otii (Baill.) Pierre ex Heckel is also evidence of their explained by the very low soil carbon content before observation capacity and the experience they had cocoa planting. Our results confirmed the clear acquired. Bidzanga et al. (2009) confirmed farmers’ advantages of cocoa agroforestry systems in improv- knowledge by showing no major difference between ing the environment for soil biological processes rankings based on these species’ mycotrophy and which affect litter composition and nutrient cycling. farmers’ classification of these species according to These advantages have already been revealed in many their fertilising properties. Moreover, in Ghana, Anim- studies (Schroth et al. 2001; Barrios and Cobo 2004; Kwapong and Osei-Bonsu (2009) highlighted the Isaac et al. 2005; Tapia Coral et al. 2005; Dawoe et al. advantages of certain native non-leguminous tree 2010). species such as Newbouldia laevis Seem. ex Bureau, The marketable cocoa yield of grassland cocoa R. heudelotii (Baill.) Pierre ex Heckel, and Spathodea agroforestry systems (mean 321 kg ha-1 after 123 502 Agroforest Syst (2012) 86:493–504

20 years) was equivalent to that of cocoa plantations to a shortage of land for growing annual food or cash in nearby gallery forests and close to yields observed crops, with a risk of reducing soil fertility in the land in forest areas in central and southern Cameroon, i.e., used for food cropping and increasing social tension. 264–500 kg ha-1 depending on the intensification The social impacts of this type of grassland affores- level (Duguma et al. 2001). This is evidence of the tation should thus be assessed. effectiveness of this local cocoa growing practice under low-input conditions, although the question as to whether these systems are capable of higher yields Conclusion with higher inputs and under more intensive manage- ment would require further research, especially on In the forest–savannah interface area in central ecological interactions between species, combining Cameroon, the afforestation of I. cylindrica grasslands both agronomic and ecological concepts and tools with complex cocoa agroforestry systems is a farmer (Male´zieux et al. 2009; Wesel et al. 2009). innovation that challenges the expert advice of cocoa The agrobiodiversity level of grassland cocoa agronomists, who consider this ecological zone as plantations in central Cameroon (Shannon–Weaver unsuitable for the cultivation of cocoa, and constitutes index of 2.07) was lower than the values mentioned by a striking example of ecological intensification by Sonwa et al. (2007) for cocoa plantations in forest local farmers. It is another example of successful agro- areas in central and southern Cameroon, i.e., 3.1–3.9 successional restoration process that is the result of and those obtained by Zapfack et al. (2002) in the same farmers’ field experience with complex plant associ- areas, i.e., 4.39. However, it was similar to that ations that evolve over time. It is also an original trend obtained by Oke and Odebiyi (2007) in cocoa in the history of cocoa growing, which has been agroforestry systems in Nigeria (2.7), by Asare and historically linked with the clearing of humid tropical Tetteh (2010) in cocoa agroforestry systems in Ghana forests. This process of setting up cocoa agroforestry (2.6) and by Salgado-Mora et al. (2007) in cocoa systems on grassland savannah integrates empirical agroforestry systems in Mexico (2.7–2.9). These knowledge and practices derived from farmers’ studies were all carried out in forest ecosystems, experience of cocoa cultivation, while also being a where it is to be expected that species diversity indices social adaptation in an ecosystem that is not very would be higher than in a forest–savanna transition suitable for cocoa growing. Moreover, this process of zone. agro-successional restoration of savannah with com- Our study showed that the expansion of grassland plex cocoa agroforests confirms the potential resil- cocoa growing in the forest–savannah interface area in ience of cocoa cultivation and farmers’ response to central Cameroon is a long-standing trend, concom- the current fears that a drier future climate could lead itant to the development of cocoa growing in forest to a decline of cocoa production in West and Central areas of central and southern Cameroon, where most Africa. Finally, this process shows that cocoa cocoa plantations had been set up between the 1930s cultivation—which is often considered to be a and the 1960s after forest clearing (Champaud 1966). deforestation driving force—can, conversely, be a Despite an apparent abundance of land resources due reforestation agent in areas that until now have been to a medium population density of around 27–30 considered to have unsuitable soil-climate conditions inhabitants km-2 (Santoir and Bopda 1995), the for growing cocoa. current increase in cocoa agroforestry systems in grassland areas raises several questions. These grass- Acknowledgments The authors would like to thank all lands, which have been collectively managed by institutions that facilitated this study: the Institut de recherche agricole pour le de´veloppement (IRAD) and the Centre de villagers until present, are traditionally used for coope´ration internationale en recherche agronomique pour le shifting food crop cultivation based on a system of de´veloppement (CIRAD), in the framework of the ‘Grand Sud fallows of at least 5 years, which is very land Cameroun’ research platform in partnership (PCP), and the two consuming (Filipski et al. 2007). The installation of projects, i.e., ‘Development of competitive and sustainable cocoa growing systems in Africa’ and ‘Strengthening cocoa plantations leads to individual appropriation of agricultural research partnerships in Cameroon’, funded by the land and a change in the land rights system. This French Ministry of Foreign Affairs. The authors thank Ce´cile grassland appropriation pattern could ultimately lead Fovet-Rabot from CIRAD for her critical proofreading. 123 Agroforest Syst (2012) 86:493–504 503

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