Wen | Xiao Liu
Editor|Xiao Liu
preface
Agroforestry is a man-made ecosystem in which plants are planted that are associated with major perennial growing species such as Robusta Coffee Agroforestry (RCA).
The latter is considered one of the main modes of perennial crop production in Cameroon, and despite the abundance of ecosystem services provided, the diversity of related species (AS) found in these RCAs and the landscape structures they form are still little known in Cameroon.
RCA structure at four sites in three Robusta coffee production basins in Cameroon, on 120 one-hectare plot units, i.e. 30 plots, timber AS and coffee trees must undergo systematic inventory and tree measurements.
Among these RCAs, 102 AS belonging to 83 genera belonging to 41 families were identified, and Ayos in the bimodal rainforest dense rainforest area had the largest number of RCA species with 71 species.
Mixed agricultural forest area
Distribution and specific types of mixed agroforestry
This is followed by Melong and Nkongsamba, with 39 and 33 species, respectively, in the unimodal rainforest area, and Malantouen with 33 species in the tall savannah of western Cameroon.
Structurally, the average planting density of coffee trees and AS is 1208-1456 plants/ha and 71-214 plants/ha, the foundation area of coffee trees is 7.29-17.40 m2/ha, and the base area of AS is 7.97-16.14 m2/ha.
From the longitudinal stratification, the 3 - 6m strata, represented mainly by introduced AS, varies from 38% to 62% depending on the site, and a series of samples show that RCA contributes to the conservation of plant biodiversity, taking into account the specific richness identified in these ecosystems.
The coffee crisis of the late 80s led to a depreciation of the market value of coffee, and producers gradually lost interest in this crop. As a result, monoculture systems, which prevailed before the crisis, were gradually transformed into mixed crop systems, especially agroforestry, with the aim of developing new sources of income by diversifying the species of interest in coffee plantations.
Agroforestry is a man-made ecosystem in which crops are grown alongside major perennial species.
These ecosystems provide people with many goods and services, and as such, they are one of the solutions to the challenges of ecological collectivization of agroecosystems.
As is the case with different agroforestry systems, interesting tree species have been found in Robusta Coffee Agroforestry (RCA) that, despite their anthropogenic state, try to mimic the landscape of natural ecosystems.
They allow the protection of many ecological functions of natural ecosystems, including air and soil conditioning, biodiversity conservation, etc. However, the landscape of these systems, ranging from simple to complex, also affects the ecological functions they provide.
This variability is conditioned by the plant diversity of the associated species (AS), in particular by its structural characteristics, which is the result of ecological environment and human activities.
Example of mixed agroforestry
Farmers have a wide range of needs in this area, for example, complex agroforestry systems with diverse and structurally complex shade canopies. It is one of the types of systems most likely to conserve important parts of primary forest biodiversity.
Data and current situation of mixed agriculture and forestry in recent years
Floral data on AS and coffee trees were collected in 30 RCAs at each site, and it was later found that the sampling design included the delineation of one hectare plot in each RCA where the data were collected, and in each plot unit, a systematic flora inventory was performed for all AS ≥ 5 cm in diameter and their properties (retained or introduced), as well as all coffee plants.
Dendritic measurements including diameter, height, and canopy diameter were performed on registered species to calculate parameters used to characterize RCA structure.
For AS, the diameter was measured at 1.3 m above the ground, and for coffee trees, measured at 20 cm above the ground, the total height and crown diameter from the ground to the top of the canopy (the coffee tree from the left end of the crown to the right end, and the projected AS from the crown to the ground) were also measured.
Diversity R was used to characterize plant diversity in RCA at study sites, and parametric texts like ANOVA and Turkey were used for apparent comparisons of variables between sites, respectively.
Using foreign Adobe to explain the landscape of RCA by site according to the data: abundance by diameter and height grade, strata, canopy diameter, and the richest AS by layer.
The following parameters are considered when characterizing the horizontal and vertical structure of RCA:
1) Ecological Importance Index; Defined by the following formula: IVI=Ar+Dr+Fr.
Structural characteristics of Robusta coffee mixed agroforestry
The following parameters were considered when characterizing the horizontal and vertical structure of RCA,
where: Ar=(ni/N)×100, where: ni=number of individuals of the species; N = total number of individuals; Relative abundance, expressed as a percentage, that provides information about the number of individuals of a species in different surveys; Dr=(si/S)×100。
where: si = cross-sectional area of species; S = total cross-sectional area; The relative advantage expressed as a percentage indicates which taxa occupies the most space in vegetation, Fr=(ri/R)×100; where ri = number of records present in the taxon, R = total number of records; Relative frequency expressed as a percentage provides insight into the social behavior of taxa and its distribution in different RCAs at the study site.
The ecologically important index ranges from 0 (no advantage) to 300 (single advantage). When IVI>2, estimate the abundance of AS stems in hectares (N/ha).
Robusta coffee agroforestry structure
According to the AS distribution of the diameter class (N/ha), coffee trees are divided into diameter grades with an amplitude of 2 cm.
While AS is divided into a diameter class of 10 cm amplitude, the base area expressed in m2/ha, S=πDi2/4, which gives an indication of the degree of competition and is an indirect measure of ground shading conditions.
Species richness and diversity index of Robusta coffee agroforestry
The flora inventory identified 102 ASs in all RCAs sampled, belonging to 83 genera and 41 families.
Ayos' RCA was found to be the most diverse, identifying 71 ASs, followed by Melong39AS, Nkongsamba33AS, and Malantouen33AS.
The Shannon Diversity Index indicates that in terms of AS diversity (3.03), it is richer than other sites.
The Simpson index ranges from 0.673 to 0.885, showing heterogeneity across sites, while Piélou's fairness index ranges from 0.414 to 0.712, showing the abundance of certain AS in the flora background of these RCAs.
Because they are irregularly distributed. The ANOVA test showed a significant difference between the diversity indices considered according to the site (ANOVA, p ≤ 0.05).
Just as Pielou's fairness shows the abundance of certain AS in the floristic background of these RCAs, the proportion of species with the most abundant functions per locus in RCA, with preserved (ASR) and/or introduced (ASI) species in RCA varies by location.
Among the RCAs at Malantouen and Ayos sites, the proportion of ASR was 68%, 67% and 63%, respectively. In contrast, Nkongsamba sites have a higher proportion of ASIs (63%), and most of these ASs with a high ecologically important index for each former site are ASIs.
Taxa of relevant species identified in RCA in the study area
Floral affinity between sites
The Sorensen index shows the flora affinity between Melong and Nkensamba on the one hand, and between Melong and Marantunin on the other, without noticing the flora affinity between Ayos and other sites.
The distribution of coffee tree abundance by diameter grade shows a general bell-shaped pattern with peak abundance levels. In Ayos and Marantunin, most people are in the 6-8 cm class. At the Nkensamba and Melong sites, the largest number of individuals were observed in the 10-12 cm and 12-14 cm diameter scales, respectively.
The AS10-20 cm scale is the most abundant at all sites, and then decreases with the increase of diameter grade; Hence the inverted " J " curve.
AS height grade stratification
AS hierarchical stratification indicates that the 3-6m strata dominated by ASI dominate all sites, with proportions of 38%, 48%, 64% and 64% in Ayos, Malantouen, Melong and Nkongsamba, respectively. In addition, the ASR-dominated 5 layers (>20m) are the least represented of all sites, with percentages of 6%, 4%, 0% and 2% in Ayos, Malantouen, Melong and Nkongsamba, respectively.
Significant differences were observed between the sites of coffee trees and AS (ANOVA, p <0.01).
These densities varied between 1456 plants/ha in Malantouen and 1208 plants/ha in Ayos, 214 plants/ha in Nkongsamba and 71 plants/ha in Malantouen.
Differences were also observed between sites for coffee and AS land area (ANOVA, p <0.05).
These base areas range from 16.14m2/ha in Maranthurn to 7.97m2/ha coffee in Ayos and 11.74m2/ha in Nkongsamba to 6.96m2/ha in Malantouen.
The average total base area (coffee tree + AS) varied between 27.14 m2/ha in Melong and 18.18 m2/ha in Ayos.
Canopy diameter, abundance and fault area of RCA.
Overview of Robusta coffee agroforestry architecture at each site
Regarding the architectural profile of RCA, the upper strata of the Melong and Nkongsamba are dense, mainly dominated by oil palm. The lower layer consists mainly of Robusta coffee, to which banana plantain and cocoa are added.
In Ayos, the upper layer is sparse and consists of a variety of ASs, including Albizia sp., Dacryodes, Petersianthus sp., and Guinean oil palm, plantain, and cocoa colonize the middle layer.
On the other hand, the lower layer is basically composed of mesocoffee trees, and in Malantouen the same trend is observed as Ayos, the only difference is that the species representing the upper layer show some differences.
RCA is characterized by the integration or protection of trees in perennial crop systems such as coffee, which is traditionally grown jointly by most farmers who protect or introduce some useful plant species in their plantations.
Several factors explain the species richness of these systems, agroforestry management methods, biophysical environment and land constraints.
In this study, species richness was found to gradually decrease from Ayos, Melong, Nkongsamba sites to Malantouen sites.
This can be explained by the fact that we are moving from the dense rainforest belt to the savannah belt, accompanied by a gradient decline in the richness of wild woody plant communities. Ayos is located in a semi-deciduous forest, and there are still a large number of plant species in the natural environment, and the degree of artificialization is not high.
In addition, the site has usable arable land, low population density (18.3 inhabitants/km 2). Composed mainly of indigenous peoples who wish to protect the natural environment, they are prone to low pressure on natural ecosystems.
In contrast, the Nkongsamba and Melong sites, which are characterized by high population density, are mainly made up of immigrants from savannah areas who generally face land-use problems.
This is reflected in the practice of unstructured mixed agriculture, the corollary of which is the management of natural resources in general and plant resources in particular, so that these migrants bring them more plant species with complementary socio-economic benefits.
The richness of the fruit species of Melong and Nkongsamba, and therefore the low Pielou fair values found at these sites, are justified.
Agroforestry management methods and planting results
Structure of Robusta coffee agroforestry
Nkensamba is a highly populated and predominantly mobile region, partly because it is more dependent on coffee sales revenue, which led it to become the third largest city in the world in Cameroon in the 1980s.
On the other hand, due to its proximity to the large urban center of Douala, and also because of the fact that there is an agricultural research station in Njombe, 50 km from Nkensamba, specializing in the production of improved fruit plant material.
In other locations, the density of these fruit varieties is lower, the Melong site, although facing the same land tenure issues as Nken Samba, has a lower population density, and in Marantunin, the isolation of the site does not provide the same market opportunities as Nken Samba and Melong.
At the horizontal structural level, AS appears densely in the RCA of Nkensamba and Melong, and sparsely in Marantunin and Ayos, due to the average fault area obtained at each station, which is consistent with the morphology of AS and its density in RCA.
Abundant non-conical AS is an undeniable source of income for producers of Nkensamba and MelongRCAs, causing their congestion and negatively affecting the development of coffee trees.
This is evidenced by coffee production at these locations, which were 184.7 kg/ha, 292.6 kg/ha, 425.9 kg/ha and 480.2 kg/ha in Melong, Nken Samba, Marantunin and Ayos.
Due to the agroecological and sociocultural environment, RCAs at Ayos sites are much more layered than RCAs at other research sites.
In fact, the producers of the site do not have enough capacity to destroy large trees and adapt their activities to the environment. These large trees are found in high strata of 12-20m and >20m and do not prevent light from lower strata from easily penetrating. Regardless of the study site, Tier 2 is the most dominant of the five layers defined in the RCA.
Due to the presence of introduced AS in this layer, they are usually medium in size and therefore dominate in layers 1 and 2, not allowing sunlight to pass easily.
Plantain and oil palm, which are also present in these two formations but are densely high in the Nkensamba and Melong sites, helping to further impede Layer 2 of 3-6m in these sites.
This layer 2 is located directly behind the layer of the coffee tree, so in these two locations, they are exposed to fierce competition for solar energy. These solar energy enters the vegetative development of plants through these ASs, however, in a complex system, it is ideal that the strata are higher than those of the main perennial species to promote the physiological phenomena that occur around the main crops.
The high density, basal area, and canopy diameter in RCA imply crowding, which negatively affects the phenology of species, and the structural characteristics of RCA are the result of management practices and reflect the architectural profile of RCA at these sites.
end
Among the species and structures associated with RCA at four production sites in the three agroecological regions of Cameroon, by comparing ecological and socio-economic conditions, the results showed that the AS and structure of RCA varied according to the biophysical and socio-economic environment of the site.
The diversity of 102 AS species identified in the RCA cannot be ignored and their contribution to the conservation of plant biodiversity cannot be ignored.
However, this variability of biodiversity, especially the structure and landscape characteristics of the site, is influenced by the agroecological and socio-economic environment, in particular the biophysical conditions and the management methods of RCAs adopted by farmers.