Eric Malézieux

Long-term dynamics of cocoa agroforests: a case study in central Cameroon

The sustainability of cocoa growing systems in the humid tropics is debatable. Socio-economic and technical data were obtained from 1,171 cocoa farmers and 1,638 cocoa plantations to assess the long-term dynamics of cocoa agroforests in central Cameroon since the beginning of the twentieth century. On-site, we estimated the age of the cocoa trees and measured their density in a sub-sample of 402 cocoa plantations. We inventoried associated woody species in 45 cocoa plantations from this sub-sample. Our results revealed a high Shannon index for the cocoa plantations (2.6) and showed that an average of 25 tree species per cocoa plantation had been planted with the cocoa trees at a density of 120 treesxa0ha−1. Surveys indicated that there had been no mineral fertilization. Nearly 70% of the cocoa agroforests were over 40xa0years old, and all farmers continuously regenerated their cocoa tree stands. Irrespective of the cocoa plantation age, the cocoa tree density remained over 1,000 plantsxa0ha−1, and fermented dried cocoa yields were 255xa0kgxa0ha−1 on average. Cocoa agroforests occupied 60% of the cultivated area on farms and cocoa sales accounted for 75% of total farm income. Almost a third of the farmers were from the area and under 40xa0years old. In conclusion, our results show that the farmers’ agroforestry practices, in addition to the fact that the cocoa tree stands were continuously regenerated and passed down between generations of farmers, could explain the long-term dynamics of cocoa agroforests in central Cameroon.

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

Cocoa cultivation is generally considered to foster deforestation. Contrary to this view, in the forest–savannah interface area in Cameroon, farmers have planted cocoa agroforestry systems on Imperata cylindrica grasslands, a soil-climate zone generally considered unsuitable for cocoa cultivation. We undertook a survey to understand the agricultural and ecological bases of this innovation. Age, cropping history and marketable cocoa yield were assessed in a sample of 157 cocoa plantations established on grasslands and 182 cocoa plantations established in gallery forests. In a sub-sample of 47 grassland cocoa plantations, we inventoried tree species associated with cocoa trees and measured soil organic matter levels. Marketable cocoa yields were similar for the two types of cocoa plantations, regardless of their age: 321xa0kgxa0ha−1 in cocoa plantations on grasslands and 354xa0kgxa0ha−1 in cocoa plantations in gallery forests. Two strategies were used by farmers to eliminate 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 fruit tree species, while preserving specific forest trees. The fruit tree and forest tree densities respectively averaged 223 and 68 treesxa0ha−1 in plantations under 10xa0years old, and 44 and 27 treesxa0ha−1 in plantations over 40xa0years old, whereas the cocoa tree density remained stable at 1,315 treesxa0ha−1. The Shannon–Weaver index increased from 1.97 to 2.26 over the same period although the difference was not statistically significant. The soil organic matter level was 3.13xa0% in old cocoa plantations, as compared to 1.7xa0% in grasslands. In conclusion, our results show that the occupation of grasslands by cocoa agroforestry systems is both an important example of ecological intensification and a significant farmer innovation in the history of cocoa growing.

Farmers’ assessment of the use value of agrobiodiversity in complex cocoa agroforestry systems in central Cameroon

Agroforestry systems in humid tropical areas are complex multispecies cropping systems whose value for farmers is often hard to assess. We present the findings of a participatory assessment that we applied to cocoa agroforestry systems. This assessment, adapted from the pebble distribution method, was used to quantify the value given by farmers to each species of their cocoa agroforestry system according to the attributed uses. A tree inventory in 50 cocoa agroforests was carried out in central Cameroon. Overall, 122 non-cocoa tree species were inventoried. The mean species richness was 23 species per plot and the mean Shannon index was 2.42, for a mean density of 180xa0non-cocoaxa0treesxa0ha−1 and 1,511xa0cocoaxa0treesxa0ha−1. Cocoa farmers defined seven different uses for tree species, including Theobroma cacao. 81xa0% of the species (including cocoa trees) had one to seven uses whereas the highest use value was given to T.xa0cacao, with a mean score of 23.6xa0%. Then, in descending order, the 10 non-cocoa species with the highest use values were Dacryodes edulis, Persea americana, Elaeis guineensis, Citrus sinensis, Mangifera indica, Milicia excelsa, Cola nitida, Citrus sp., Ricinodendron heudelotii, and Terminalia superba. The frequency of non-cocoa species was significantly and positively correlated with their use value (R2xa0=xa00.914). Our results showed that technical innovations designed to improve cocoa agroforestry systems should take into account farmers’ knowledge to propose them systems so as to be able to more effectively address their expectations.

Using 3D architectural models to assess light availability and root bulkiness in coconut agroforestry systems

Using 3D architectural models to assess light availability and root bulkiness in agroforestry systems. In many parts of the humid tropics, coconut trees are frequently intercropped with food crops, or tree crops such as cocoa. The performance of such systems depends on planting patterns, but also on growing conditions for crops below the coconut canopy throughout the development of the coconut trees. We used a modelling approach providing indicators for assessing above-ground competition for light and below-ground competition for space, in order to optimize intercropping in coconut smallholdings. Light transmission and the number of coconut roots in the interrow were assessed in coconut smallholdings from 6 to 60xa0years old. The modelling of light transmission through coconut stands was based on three-dimensional virtual coconut trees and a numerical light model that computed the shade cast by coconut trees on underlying crops. Root colonization in the interrow was assessed with virtual 3D coconut root systems. Our results showed that intercropping with shade-tolerant species was not limited by light transmission from the 35th year after coconut tree planting. However, at that stage of coconut tree development, the density of primary roots in the interrow limited intercrop development, especially for root and tuber crops. Alteration of the planting pattern over time increased light transmission but did not significantly affect root density. This modelling approach, which involved little parameterization that was easily done, appeared to be an efficient tool for recommending coconut tree planting patterns and densities, as well as indicating intercrop potential depending on their location in the most sunlit areas with minimum root competition.

Semi-wild palm groves reveal agricultural change in the forest region of Guinea

In West Africa, natural regeneration of oil palms (Elaeis guineensis Jacq.) can be favoured by agricultural practices. The structure of palm groves may thus reflect the history of land use. In this study, we examined the connection between biophysical factors, land use and the structure and dynamics of semi-wild palm groves in the village of Nienh, in the forest region of Guinea (Forest Guinea), in order to determine to what extent semi-wild palm groves could be considered as an ecological indicator of the history of regional landscapes. Grove management strategies of farmers were also determined and related to farm characteristics. In Nienh, semi-wild palm groves were found in three cropping systems with differing characteristics in each. Palms were scarce in lowland agricultural areas (8xa0palmsxa0ha−1), while they were significantly taller (15.8xa0m on average) and less dense (36xa0palmsxa0ha−1) in agroforests than in slash-and-burn cropping systems (9.4xa0m and 55xa0palmsxa0ha−1 respectively). Interviews with farmers showed that it was possible for a farmer to have a global strategy of semi-wild palm grove densification combined with oil palm elimination on a plot scale. The lack of regeneration of palms in agroforests resulted from the almost systematic elimination of young palms by farmers. Conversely, in slash-and-burn cropping systems, young palms were often preserved. As the structure of semi-wild palm groves was partly explained by agricultural practices, it could be used as an ecological indicator of changes in practice in relation to socio-economic context.

Structure and dynamics of coconut-based agroforestry systems in Melanesia: A case study from the Vanuatu archipelago

Coconut (Cocos nucifera)-based agroforestry systems hold promise as a sustainable land use activity in the Melanesian islands, where food dependency on foreign sources and land shortages are increasing dramatically. This chapter describes the dynamics of these smallholder production systems in the Malo Island of northern Vanuatu (Melanesia), where a dual economy operates in which resources are dedicated to both subsistence and commercial production. The floristic elements found in the coconut plantations were typical of those described in the humid tropical homegardens elsewhere, with an average of 12 tree species per plot. Mean Shannon Weaver index was 1.57 with the vertical profile of vegetation having one-to-five strata. Although the coconut palms dominate these production systems, in certain cases other trees may dominate it. Situations in coconut plots evolve throughout the development phase of the palms. Based on that, five types of smallholder coconut-based agroforestry systems were recognized, which falls into two main evolutionary patterns: (1) a perennial occupation of the cultivated land by coconut trees, because of coconut replanting, and (2) a gradual return to tree fallow in which the coconut palms gradually disappear because of changes in the complex multistrata vegetation. (Resume dauteur)