Practice and Biodiversity of Informal Ornamental Horticulture in Kinshasa, Democratic Republic of Congo

1. Introduction

The recent strong urbanization expected worldwide is attracting all attention, particularly in terms of urban resilience strategies and practices [1,2,3]. It is indeed recognized that urbanization profoundly affects biodiversity, ecosystem processes and services, climate and environmental quality [4]. It is therefore useful to study and control all urban practices, whether or not they are detrimental to biodiversity [5,6]. These include ornamental horticultural practices, which have so far received little attention in African cities [7].

The lack of attention paid to ornamental horticulture in African cities is due to the fact that, when it comes to urban planning, the importance of aesthetics is often underestimated, and the link between quality of life, social progress and other elements of well-being is underdeveloped [8]. In addition, pervasive poverty forces populations to make choices oriented primarily towards food and economic security [9]. As a result, urban populations increasingly prefer to preserve edible rather than ornamental species in their living space [7,9].

In this trend towards the simplification/homogenization of urban ecosystems through choices made by households, a probable loss of diversity in ornamental plant species is to be feared in the medium term [10]. Yet these species are necessary not only for the balance of environments, but also for numerous industrial productions such as essential oils [11,12,13].

The growing disinterest in the cultural and aesthetic value of nature is what Occhiuto [14] refers to in part as the “abstraction of the Man-Nature relationship”. This is clearly evident in Kinshasa, the capital of the Democratic Republic of Congo (DRC). Once known as “Kin-the-beautiful”, the city of Kinshasa is now described as “Kin-the-trash” [15,16]. In fact, in colonial times, Kinshasa was composed, at least in its urban part, of beautiful landscapes of squares, hedges of ornamental plants, gardens and flowerbeds and traffic arteries embellished with ornamental species [16]. It should be noted that, at this time, ornamental horticulture was of great importance in the country, as demonstrated by the creation during the same period of trial gardens (e.g. Kisantu in Kongo-Central and Eala in Mbandaka) for tropical ornamental plants of economic interest, in order to acclimatize and disperse them throughout the country [17]. This enthusiasm for floriculture, which was accompanied by the creation of several horticultural enterprises, unfortunately gradually died out after political independence in 1960 [18]. Yet, given the DRC’s wealth of spontaneously-grown ornamental plants, maintaining the colonial-era enthusiasm for floriculture could have helped generate an important local economic sector, but also one for export, as is the case in Kenya [19] and India [20].

Fortunately, in the city of Kinshasa, ornamental plant nurseries have proliferated along traffic arteries for several decades considered in this study as “informal horticultural sites” (IHS) [9,21].

This activity, which is increasingly attracting large numbers of Kinshasa residents, represents not only a phytodiversity market and a major mobilization of exotic and indigenous biodiversity, but also a renewed interest in amenity species in the city’s (peri-)urban areas. This sector, which is developing informally in Kinshasa, is poorly understood in a number of respects, such as the people involved, the benefits derived, the species exploited, seed acquisition methods, production conditions and the risks of biological invasion [22,23].

It is therefore important to fill this gap to better control the circulation of species, limit biological invasions and better guide strategies for the conservation of peri-urban phytodiversity. Thus, the present study aims to provide a better understanding of this phenomenon of IHS proliferation in Kinshasa through the following three questions: (i) what is the profile of the producers engaged in the activity? (ii) Under what conditions do they ensure the production of ornamental plants in the different sites? (iii) What ornamental species do they produce; their diversity in terms of biological types, their invasive status and their conservation status? Studies carried out on this ornamental horticulture activity in towns in Togo [24] and Quebec [25] show that it is the preserve of young people, often trained on the job, and that the species produced are often largely of foreign origin. On this basis, we approach the present diagnostic analysis of IHS in Kinshasa, under the assumptions that: (i) they employ mostly young people of all levels of education and improvised in the trade; (ii) their production conditions (access to production space, acquisition of seeds, use of phytosanitary products, conditioning of plants and existence of any support) are similar from one site to another and (iii) the species produced are mostly exotic and include threatened and potentially invasive species and are mostly phanerophytes.

2. Materials and Methods

2.1. Study Area

The study was carried out in the city-province of Kinshasa (VPK) located in the south-west of the DRC, precisely to the south of the Malebo Pool, a widening of the Congo River (Figure 1). The VPK covers an area of 9965 km² and is administratively subdivided into 24 municipalities, 15 of which are urban, 4 peri-urban and 5 rural according to their morphological building criteria [26]. The city site is structured into two morphological units: the “lower city” on the plain at an altitude of almost 300 m, covering 200 km², and the “upper city” on the hills rising to an altitude of 600 m, covering 240 km² [16]. The lower town concentrates the major arteries and roads that structure the city, as it includes the urban center, notably the municipality of Gombe. This is where we find informal horticultural sites (IHS) set up along the roadsides. The upper town, on the other hand, is home to the majority of informal settlements without adequate roads. The climate of the VPK is tropical humid AW4 according to the Köppen- Geiger classification [27].

It is characterized by two seasons, one rainy (October to May, with a short interruption from late December to mid-February) and the other dry (June to September). Average annual rainfall is around 1430 mm [28]. If the natural vegetation of the Kinshasa region was composed of dense forest, savannah and semi-aquatic and aquatic formations in the valleys and around the Malebo Pool [29], it would gradually be replaced by grassy savannah and fruit trees concentrated in inhabited plots, particularly in the peri-urban zone [30].

The VPK has over 17 million inhabitants, the majority of whom are young, with an age structure comprising 48.3% aged 0 to 14; 49.4% aged 15 to 64 and 2.3% over 65 [30]. In 2005, the VPK had an incidence of poverty of 41.6%, with gender and level of education of the head of household as explanatory factors. It has a low activity rate (42.3%) compared with the national average (60.2%) and a high level of underemployment, which concerns 53.1% of the employed. The latter are generally engaged in the informal sector, which is the main provider of jobs in Kinshasa (65.6% of jobs and 89.5% of Kinshasa household income) according to SOSAK [30].

2.2. Sampling and Data Collection

A total of 15 informal horticultural sites (IHS) were sampled (Figure 1) and surveyed using the so- called “snowball” technique [31]. This involved starting the survey with the IHS closest to the University of Kinshasa (UNIKIN) campus. Sampling was stopped when the number and list of ornamental species reached saturation.

This procedure yielded a total of 178 respondents. The use of this sampling method is justified by the lack of statistical data on the distribution of IHS in the city.

Three categories of data were collected, covering the period from October 2022 to July 2023. The first category concerns the characterization of the socio-professional profile of workers in the various IHS. This includes workers’ gender (male, female or other), employment status (employer or employee), marital status (married, single or other), age group following the city’s age pyramid (under 18, 19–25; 26–35; 36–45; 46–55 and over 56), level of education (No education, primary, secondary, university), retraining and/or training related to the nursery trade (apprenticeship or improvisation), whether or not they had another activity, and length of time in the trade (years of experience in the trade: less than 2 years, 3–5; 6–8; 9–12; more than 12 years) and other secondary activities. The second category of data focused on the conditions of production of IHS, notably the mode of acquisition of production space (by tacit or formal contract), the existence or not of taxation (annual tax or no tax), the mode of acquisition of seeds (by purchase, by picking or by multiplication), the way seedlings are packaged (in plastic bags, hard plastic pots, paper bags or concrete pots), whether or not phytosanitary products are used, whether or not they benefit from any form of support, and whether or not they belong to a professional association. The last category of data relates to the list of ornamental species produced, their origin, biological type, invasive status and their conservation status. The definition of an ornamental plant or species is still a matter of debate [32]. We agree to adopt the widely accepted definition according to which an ornamental plant is a plant cultivated for its ornamental qualities, rather than for its nutritional or industrial value. Such a definition distinguishes ornamental species from fruit, medicinal and vegetable species [11].

2.3. Data Analysis

To test our hypothesis concerning the socio-professional profile of IHS, we subjected the corresponding data to hierarchical ascending classification following a principal component analysis in order to group IHS as similarly as possible. The analysis was carried out using R software and the FactoMineR package [33]. This approach makes it possible to account for characteristics common to different groups of IHS. We then performed a Fisher exact test [34] on each of the production condition parameters to see whether the distribution of horticulturists in the different IHS groups formed is random. Such a procedure enables us to verify our hypothesis of similarity of production conditions between the IHS, depending on the number of recognized parameters linked to the distribution into IHS groups carried out. With regard to the species inventoried, we first checked their names, then determined their family and origin (exotic or indigenous) using available documents [35,36] and, in addition, online resources, notably the “African Plants Database”, “International Plant Names Index (IPNI)” and “The Plant List” websites. The data thus generated enabled us to determine the relative proportions of genera, families and origins of species in order to highlight any predominance.

The biological types of the plant species inventoried were established according to the definitions of Raunkiaer [37], which take into account the position of the buds, the type of unfavorable climate and the size of the individual. Only the main categories were used: therophytes (Th), hemicryptophytes (Hem), geophytes (Ge), chamephytes (Ch), epiphytes (Epi) and phanerophytes (Ph). To determine the invasiveness of plant species, the Global Invasive Species Database [38] was consulted. Species conservation status was analyzed using the International Union for Conservation of Nature Red List database [38]. The observed statuses are: Extinct (EX), Extinct in the Wild (EW), Critically Endangered (CR), Endangered (EN), Vulnerable (VU), Near Threatened (NT), Least Concern (LC), Data Deficient (DD) and Not Evaluated (NE).

3. Results

3.1. Socio-Professional Profile of Horticulturists

Most informal horticultural sites (IHS) are made up of groups of people, each of whom owns a batch of plants. The results of a multivariate analysis based on numerical classification applied to the socio-professional characteristics of IHS enable us to group them into five relatively homogeneous groups (Figure 2).

Group I comprises nine sites (sites 2; 3; 4; 7; 8; 9; 10; 11; 12), Group II three sites (sites 1; 13; 15), Group III site 14, Group IV site 6 and Group V site 5. Table 1 shows the socio-professional profile associated with each of these groups.

Group I corresponds to sites where certain socio-professional parameters have low values: an average of 2 employers and 0 employees, an average of 1 single person, individuals in the 19 to 25 and 26 to 35 age brackets with no formal education, workers who have actually learned the trade and those who have improvised, workers with or without horticultural activity and with reduced seniority (< 2 years and 3-5 years) in the trade.

Group II is characterized by sites whose socio-professional parameters match those of the average of all sites. This is the group of sites with average socio-professional characteristics, i.e. 8±12 employers and 4±8 employees. Group III is made up of sites with a very low number of non- educated people. These sites have the same values as the average site for all other socio- professional parameters. As with the previous group, Group IV is made up of sites with the same values as the average site for all socio-professional parameters, except for the number of very old people (>56 years), which is higher than the average. Group V represents sites where the socio-professional parameters have much higher values than the average. These are sites with a large number of workers in their fifties.

Apart from these differences between the groups of sites identified, we note that they are made up exclusively of males, with individuals of varied but young age brackets (between 19 and 45), and of equally varied levels of education and seniority in the trade. Most of them are newcomers to the trade (Table 1).

3.2. Production Conditions for Horticulturalists

The results of the applied ANOVA indicate that the production area occupied by each horticulturist is not significantly different between the IHS groups identified (F ≈ 1.58; p-value > 5%). The average area of individual production space obtained is 33±4 m² with a relatively high coefficient of variation (CV) of 61%, suggesting the wide variation that exists between production areas.

Table 2 also shows that the groups of sites show statistically significant differences for seven of the twelve characteristics of production conditions considered. These are the mode of acquisition of the production space, the existence of taxation, the use of paper bags or hard plastic plugs or concrete pots for packaging seedlings, the use of phytosanitary products and the organization into associations.

The mode of acquisition of production space by formal contract is the predominant one for all groups, except for group II where it is rather the tacit contract. Consequently, the non-existence of taxation for production space is more remarkable for group II.

With regard to plant packaging (Figure 3 and Table 2), all groups except group III use paper bags, with group V being the most abundant (60% of growers). Similarly, all groups use hard plastic pots, with group V using the most (50% of growers). On the other hand, only Group I uses concrete pots, and only to a small extent (24% of growers). We also note that a large proportion of growers in the various groups use plant protection products. In particular, all growers (100%) in groups III and V use them, and are organized in associations in proportions of 50% and 100% respectively.

With regard to the other five characteristics of production conditions, we note that for all horticultural sites, three modes of seed acquisition coexist: occasional purchase, picking and multiplication. Likewise, all the sites use plastic bags indiscriminately to package seedlings, and none of them benefit from support from any structure.

3.3. Cultivated Species, Their Origin, Biological Type, Invasive and Conservation Status

A total of 139 ornamental species in 119 genera and 62 families were inventoried at the sites surveyed (Table 3). The five most represented genera are Begonia (3%), Acalypha (2%), Alternanthera (2%), Kalanchoe (2%) and Senna (2%), with the remaining 144 genera accounting for 88%. Similarly, the five most abundant families are Araceae (9%), Fabaceae (6%), Asteraceae (6%), Amaranthaceae (5%), and Euphorbiaceae (4%), with the remaining 57 families accounting for 84%.

Furthermore, we note that the majority of ornamental species are exotic (91%) and only 8% are indigenous. Moreover, species of uncertain origin (1%) are likely to be foreign to the study area. A total of 106 species (76%) were quantified as non-invasive and 33 species (24%) as potentially invasive (Table 3).

The results of the biological types of the different ornamental species in the IHS of the city of Kinshasa show a dominance of phanerophytes (37%) which are trees and shrubs but also woody lianas that can grow up to the cymes of the largest trees. Other biological types, notably hemicryptophytes, geophytes, therophytes, epiphytes and chamephytes, account for 27%, 17%, 9%, 6% and 4% of species recorded respectively (Figure 4).

According to the IUCN Red List, of the 139 species listed, one (0.72%), Caladium bicolore (Aiton) Vent. is Critically Endangered (CR), 5 species (4%) are Endangered (EN), Ananas comosus (L.) Merr, Costus sanguineus Donnell Smith, Begonia eminii Warb, Pandanus furcatus Roxb, Phlox drummondii Hook, 3 (2%) are vulnerable (VU), Araucaria heterophylla (Salisb.) Franco, Begonia glabra Aubl, Biophytum Zenkeri Guillaumin; 2 (1%) are Near Threatened (NT), Dahlia coccinea Cav. and Argemone mexicana L.; 3 (2%) are Data Deficient (DD) and 52 (37%) are Not Evaluated (NE). On the other hand, 73 species (53%) are in the LC category, i.e. of minor conservation concern (no threat) (Figure 5).

4. Discussion

4.1. Methodology Approach

This analysis of informal horticulture in Kinshasa is based on snowball sampling [31]. The main drawback of this method is the bias generated by the relatively informal process of sample constitution. While it is therefore difficult to produce unbiased estimators for the characteristics of the population itself, it is nevertheless possible to make inferences about the parameters of the network of relationships [40]. This is precisely the aim of the present study, which seeks primarily to gain a better understanding of the structure of the horticulturists’ network. The data collected on the species produced were confined to species listing, grower characteristics and production conditions. Due to their sensitivity, economic and financial data were not addressed. It is important that other, more specific studies with an adapted approach address these aspects for a complete understanding of the related challenges.

4.2. Contrasting Characteristics of Informal Horticultural Sites in Kinshasa: The Need for Horticulturists to be Supervised

Five groups of informal horticultural sites (IHS) are distinguished according to their socio- professional profile. This classification reflects the physical reality of the workers in the different IHS. Indeed, while some IHS sites, such as site 7 (1st street Saint Raphaël) in group I, have few young or old workers, others, such as site 5 (Avenue of clinic) in group V, have an impressive number of workers. Such variation in IHS composition can be explained by their location in the city, not only in terms of the availability of production space, but also the existence of potential demand in the surrounding area (Figure 6).

Furthermore, Kinshasa’s IHS employ a large number of people (a total workforce of 178 for 15 sites) compared with other cities where the same activity is developing, such as the cities of Atakpamé, Lomé and Kpalimé in Togo, which in 2013 had a total of 179 workers for 55 sites [24]. This could be explained by the fact that Kinshasa is a more populous city with a high unemployment rate [41]. What’s more, just as in these same Togolese cities, IHS in Kinshasa employ mostly young people between the ages of 19 and 45, thus confirming our related hypothesis. However, Kinshasa’s IHS include all levels of education, but both employers and employees are for the most part improvised in the trade. The same observation has been made in cities in developed countries such as Quebec, in a report by the Institut québécois des ressources humaines en horticulture [25], which recommends the organization of training courses in horticulture and landscaping.

The activity of informal ornamental horticulture thus appears as a convincing example of the famous “débrouillardisme” or “mayele” (in Lingala, one of the vernacular languages) developed in Kinshasa to curb the poignant crises of unemployment and poverty [15]. It is therefore also, as the people of Kinshasa put it, an implementation of Article 15, a fictitious article of the Constitution that would stipulate: “débrouillez-vous pour vivre”[30].

We also note that, unlike other African cities such as Togo [13], ornamental horticulture is exclusively a male activity in Kinshasa. Indeed, although it can bring in income, ornamental horticulture is not directly linked to the daily life of the Kinshasa woman. Instead, she is preoccupied with and attracted to activities directly linked to the socio-economic life of the household, such as market gardening for vegetables, petty trading for basic necessities and so on.

Seven out of the twelve production condition parameters showed significant differences between the different IHS groups (Table 2). Our hypothesis about the similarity of production conditions between the IHS sites is therefore partially invalidated. The production area of most sites is often located on the edge of busy thoroughfares and in front of a public structure (ministry, directorate, traffic circle and other administrative services) or private structure (school, hotel, shop, residence). Consequently, contracts for the acquisition of these spaces are either tacit, based on oral or de facto authorization from the corresponding public or private authority, or formal, based on an occupancy authorization document. Whatever the case, the mode of acquisition of production space remains precarious and maintains a permanent insecurity of land tenure in the activity, as also reported in Togo [13]. As some of the producers interviewed explained, they work under the constant threat of being evicted at any time by the owners of the public or private space they occupy. It was these repeated threats that prompted the growers on site 5 (avenue of clinic in the commune of Gombe) to organize themselves into an association and hire a lawyer to defend them.

In addition, we note that seeds and seedlings are obtained in a variety of ways (occasional purchase, collection, multiplication) (Table 2). This allows the necessary dissemination of ornamental plant genetic resources. Nevertheless, in view of the risks of invasion strongly correlated with ornamental horticulture [23,42,43,44], the circulation of these plant genetic resources must not be prohibited, but secured by alerts on potentially invasive species. A prime example, well known to the Congolese as “Congo ya sika”, is the water hyacinth (Eichhornia crassipes (Martus) Solms In A. DC.). This species, originally from Brazil, was introduced into the Congo shortly before independence to decorate water features, from where it escaped to invade the Congo River [45]. There is therefore a need to provide support to growers, who to date have received no assistance what so ever, probably due to their informal status. This support could include technical assistance on the proper use of phytosanitary products or alternative products to protect the urban environment and workers’ health.

The latter are exposed to health risks as a result of coming into contact with a wide range of plant and chemical substances [46].

Variations in seedling conditioning methods (Table 2) can be explained by the associated investment costs. Packaging seedlings in concrete or hard plastic pots requires considerable investment. Plants packaged in this way are expensive and therefore difficult to sell on the market. As a result, some growers choose to produce certain types of packaging only to order. The range of packaging methods for registered seedlings is limited and excludes an important local market.

These include, for example, the market for wreaths for the many funeral ceremonies or matanga (in Lingala) and the market for bouquets of flowers for the many wedding ceremonies or libala (in Lingala) held in Kinshasa. These markets are currently being flooded by the plastics industry, and so appear to be a loss of earnings for producers, given the large number of matanga and libala events held in the city.

We noted a total number of 139 ornamental species produced in the 15 IHS we visited. This number is still comparable to, but higher than, that recorded in the city of Dakar, i.e. 109 species in 59 stations [8], but by far low compared with the number of over 600 ornamental species reported by Radji et al. [47] in the cities of Lomé, Atakpamé and Kpalimé in Togo. There are two main reasons for this difference. The first relates to the definition of the ornamental species under consideration. Radji et al. [47] considered a very broad definition of ornamental species, including known species cultivated primarily for their edibility but often found in private or public gardens, such as mangifera indica L. Nevertheless, as Allain [32] points out, the definition of a plant’s ornamental status remains relative and variable in time and space, depending on changing needs and uses. The second reason relates to the inventory approach employed. Our inventory was limited to horticultural sites, whereas Radji et al. [47] extended it to parks and gardens. We note, however, that Kinshasa’s IHS maintain a size able market in phytobiodiversity. As reported elsewhere, such as in the cities of Togo [24], most of these species are exotic. Clearly, a major effort still needs to be made by all stakeholders to promote indigenous species.

Concerning the result on species biological types, we noted the dominance of phanerophytes. The dominance of phanerophytes is reported in urban environments [8,48,49,50]. Phanerophytes are in high demand in cities, as they adapt better to the rather harsh climatic and edaphic conditions of the city [51]. What’s more, because of their size, they are able to provide shade in all seasons, a very important service in urban environments [52].

Furthermore, the presence of a significant number (33 species) of potentially invasive species confirms Hu et al. [53] observation that ornamental horticulture is a major vector of invasive plants. This underlines the importance of controlling the circulation of plant species through the informal horticultural sites studied. These sites contribute to the reproduction/multiplication of species that are important from the point of view of biodiversity conservation. They are home to a significant number of moderately to highly threatened species.

4.3. Implications for urban biodiversity conservation

This study highlights several implications for the conservation of phytobiodiversity and urban planning, namely: the professionalization of informal horticultural site managers, the introduction of monitoring of the circulation of potentially invasive species, and the promotion of indigenous species in urban landscaping.

5. Conclusions

This study provides a diagnosis of the informal horticultural sites (IHS) that are proliferating in Kinshasa. Analysis of the socio-professional profile of these IHS has enabled us to classify them into five groups. The IHS employ exclusively men, most of whom are improvised in the trade, from all levels of education and for the most part in the 19 to 45 age brackets. We also note that IHS offer employment or income to a significant number of people, and therefore households.

Production conditions are relatively similar from one site to another. Nevertheless, the study reveals that IHS sites are characterized by permanent insecurity of land tenure, the use of phytosanitary products and plant conditioning methods that are not very diversified and calibrated to growers’ investment capacities.

Furthermore, thanks to the diversified ways in which growers acquire seeds, IHS encourage the dissemination of ornamental plant genetic resources, which should be safeguarded by issuing warnings about species at risk. Our results also show that IHS provide a significant market for phytobiodiversity, with at least 139 ornamental species, most of them exotic, including 33 identified as potentially invasive.