Background and aims – Cinchona (Rubiaceae) tree bark is the key source of quinine alkaloids used as malaria treatment. Cinchona trees were introduced to Democratic Republic of the Congo (DRC) in the early 20^th century. Currently, the eastern DRC accounts for an estimated 55% of the global supply of quinine. The aim of this study is to obtain more insights into what context Cinchona is cultivated, what the scale of the farming and its management is, and how specific risks are being dealt with.

Material and methods – Data was collected on Cinchona tree distribution, socio-economic variables, farm characteristics, and cultivation techniques based on interviews with 185 smallholder farmers in five regions (groupements) across the eastern DRC.

Key results – Most Cinchona trees are grown at elevations between 1588 and 1627 m a.s.l. and most farmers preferred growing C. calisaya in a monoculture cultivation system, with in vivo propagation, and their own seed sources. Cassava was the dominant crop as previous cultivation and as a crop grown together with Cinchona. Eucalyptus was the dominant tree species grown together with Cinchona. Furthermore, most of the farmers apply a 1 × 1 m spacing and most do not use any additional fertilizer input. The most reported plant disease is linear canker.

Conclusion – To sustainably increase the productivity of Cinchona in the DRC, smallholder farmers should be given appropriate training to empower them to carry out their own in vitro propagation and apply integrated soil fertility management and integrated pest management. Our results provide information on current cultivation of Cinchona in the DRC, which may become more important given the rising resistance of the malaria parasite against other medicines.

Cinchona, cultivation techniques, farm characteristics, silviculture, socioeconomics, tropical tree, quinine

Malaria, caused by the parasite Plasmodium, remains one of the most prevalent diseases in the world (Sato 2021). In 2022, an estimated 249 million cases of malaria were registered, of which 94% occurred in the African continent (WHO 2023). Malaria can be treated with medicines inhibiting the growth of parasite and quinine was the first effective and oldest anti-malarial cure available. Quinine is obtained from the bark of the Cinchona L. tree (family Rubiaceae) and it is a natural alkaloid that has been used for centuries as prophylactic measure for treatment of malaria (Achan et al. 2011).

Cinchona calisaya Wedd. is one of the 24 species recognised in the genus Cinchona (POWO 2024). It is the species with the highest quinine concentrations identified to date (Maldonado et al. 2017). The four major alkaloids that are produced in Cinchona are quinine, quinidine, cinchonine, and cinchonidine (Achan et al. 2011), which are mainly extracted from the bark of the trees. Quinine concentrations in the bark of twigs, trunk, and roots vary significantly, between 1 and 14% (Nair 2010). The use and importance of natural quinine is still significant and even increasing. This is attributed to 1) the increasing resistance of malaria parasite to other antimalarial drugs (e.g. chloroquine), 2) the low price of natural quinine, and 3) the supplementary use of natural quinine against tick-borne diseases in cattle.

Cinchona trees are native to the Andes of South America, roughly from Colombia over Ecuador and Peru to Bolivia, and they occur between 800 and 3000 m a.s.l. (Wasis and Sandra 2020). Conventionally, Cinchona trees are mostly vegetatively propagated, coppiced, and the bark is harvested every 6–10 years (Nair 2010). Due to historical exploitation and habitat destruction, several species of Cinchona are relatively rare in their native range and even vulnerable to endangered, according to the IUCN Red List (García et al. 2022). Thus, Cinchona is of conservation concern in South America.

Europeans learned of the medicinal value of Cinchona bark in Ecuador in the 17^th century, and quickly exports of Cinchona bark from South America to Europe were reaching half a million kilograms of bark per year (Maldonado et al. 2017). As import could not meet the demand, a quest began to establish resources of Cinchona by the British, Dutch, and French empires from the 1850s onwards. Cinchona was first widely cultivated in Southeast Asia in former British and Dutch colonies particularly in Indonesia, India, and Sri Lanka, where its current production declined due to economic, geopolitical, technical, and phytosanitary reasons. Accordingly, C. calisaya and C. pubescens Vahl have been cultivated in several countries in South America, Asia, and Africa (De Pessemier 2020). Today, 55% of global quinine production (via Pharmakina SA, www.pharmakina.com) occurs in the Democratic Republic of the Congo (DRC), most likely using seeds obtained from Bolivia (De Pessemier 2020).

However, we lack a good understanding of the local supply chain of Cinchona by smallholder farmers. Therefore, the main aim of this study is to obtain more insights into what context (agronomic, socio-economic, and ecological) Cinchona is cultivated in the DRC, what the scale of the farming and its management is, and how specific risks are being dealt with.

Cinchona, the source of natural quinine used in the prevention and therapy of malaria, was introduced to tropical Africa in the 1850s and widely grown in plantations. As a consequence, the eastern part of the DRC is a major production centre today. This can be attributed to the favourable climate in the area, which is similar to the native conditions in the Andes with an elevation range of 1,450 to 3,330 m a.s.l. (González-Orozco et al. 2023). Our findings indicate that climate is a key biophysical variable influencing Cinchona distribution in the DRC. Orwa et al. (2009) reported that a mean annual temperature of 10–23°C and a mean annual rainfall of 1,020–3,800 mm is ideal for Cinchona production. Elevation is indeed a key biophysical variable driving the distribution of Cinchona in each groupements (Fig. 2C). However, Cinchona production is being constrained by the shortage of land and the limited number of fields per farm in the study area. For instance, the majority of Cinchona farmers (68%) at Baswagha have a maximum land holding of 10 ha. Also, the smallholder farmers across the five groupements typically possess between two and five fields of Cinchona per farm, with some having fewer than two fields per farm. Similarly, De Schaepmeester (2021) reported that the Cinchona plantations in Africa are currently mainly in the form of smallholder farms of different sizes, but the lack of productive land is their common constraint. Cinchona bark yield identified here ranged from 0.8 to 2.4 t ha^-1. This is a much lower yield compared to the bark yield in India, which is about of 9,000 to 16,000 t ha^-1 (Jäger 2014). The lower yield in the study areas could be attributed to lack of reliable sources of seeds, diseases and insects’ attacks, no or low use of fertilizers, and poor and declining soil fertility. The proportion of the total farm area occupied by a given crop at household level may indicate the economic importance of the crop. For instance, 71% of the farming households at Baswagha used more than half of their land for Cinchona production, while for 67–88% of the farming households in the remaining four groupements, the land occupied by Cinchona was less than 25% (Fig. 4A). This indicates that most smallholder farmers at Baswagha used the majority of their available land for Cinchona production. Also, Cinchona production is mostly concentrated at Baswagha because Cinchona producers are looking for disease-free areas to expand their production, and this is also an area less troubled by conflict. Boa (2015) also reported that the initial Cinchona plantations established from the 1930s onward were around Bukavu in South Kivu. These continued to flourish until regional conflict disrupted business in the late 1990s, which worsened after losses due to Phytophthora root rot. Cinchona is grown in monoculture and mixed (multiple) cropping systems in the study areas. Monoculture is the most common cropping system of Cinchona production for the farmers at Baswagha, Kabare, and Ngweshe. However, multiple cropping is the most popular cropping system for the farmers at Ntambuka and Rubenga because these are the regions where Cinchona is relatively less important. Munyakazi et al. (2022) reported that multiple cropping is the dominant cultivation system for 92% of the farmers in South Kivu, while the remaining 8% of the farmers practice monoculture.

Cassava is a dominant crop in the previous cultivation and among crops associated with Cinchona. Karume et al. (2022) reported that agroecological conditions of areas suitable for cultivating staple crops, mainly cassava, beans, rice, bananas, potatoes, coffee, tea, cocoa, and sugar cane, are also conducive for growing Cinchona in the DRC. These results indicate that cassava is highly associated with Cinchona, and it is a staple crop grown by the farmers for food security. The main reason that persuades farmers to opt for a mixed cultivation system is the risk reduction in the face of various hazards in the agricultural sector that can also affect their farm income and food security. So, over 15 million tons of cassava are produced yearly and cassava alone accounts for > 70% of all food production in the DRC (Karume et al. 2022). Tabaglio et al. (2023) also reported that cassava is a mainstay crop for food security in the DRC. Similarly, Orwa et al. (2009) reported that Cinchona is intercropped with food crops such as beans and other legumes in Central Africa to prevent soil erosion. Concerning trees associated with Cinchona, Eucalyptus, and Grevillea, exotics to the DRC, are the major tree crops associated with Cinchona at Baswagha, Ngweshe, Rubenga, and Ntambuka (Fig. 4E).

The Cinchona propagation technique did not vary among smallholder farmers in the study areas. Almost all the farmers at Baswagha, Kabare, Ntambuka, and Rubenga used in vivo propagation. They may prefer the in vivo propagation approach because it preserves the beneficial traits of the parent planting materials (Wasis and Sandra 2020), while only 3% of the farmers at Ngweshe hybridize their plants. In addition, all of the farmers at Baswagha used their own seed while farmers in the other four groupements used other seeds from market and other smallholder farmers.

The source of seeds for regeneration of new plants used for Cinchona production varied among the groupements in the study areas. This indicates that there is a lack of improved seeds, reliable source of seeds, and an absence of farmer’s cooperatives supplying improved agricultural inputs for sustainable intensification of Cinchona production in North and South Kivu. Similarly, most cropland in Sub-Saharan Africa is characterized by low crop productivity and poor soil health due to long-term nutrient mining and soil carbon decline, which present major constraints for sustainable intensification (Vanlauwe et al. 2014; Mungai et al. 2016).

Several studies have been conducted to assess the local knowledge of farmers on the fertility status of their soils. So far, the research conducted in the study areas mainly focused on documenting how farmers classify the fertility status of their soils (Corbeels et al. 2000). On average, 61% of the farmers at Ngweshe, Ntambuka, and Rubenga classified the fertility of their soils as average, while the farmers at Ngweshe and Rubenga classified the fertility status of their soils as poor. Poor fertility of soils in the study areas could be attributed to no or low use of fertilizers. For instance, 62% of the farmers used no fertilizers across the groupements, although fertilizer application is believed to be responsible for at least 50% increase in crop yield in the 20^th century (Krasilnikov et al. 2022). For maximum productivity and quality of Cinchona, fertile soil with good availability of essential plant nutrients such as nitrogen, phosphorus, and potassium are crucial. Similarly, in Congolese C. calisaya samples, an increase in quinidine and cinchonine concentrations was observed for a higher level of plant nutrients (115 kg N, 105 kg P₂O₅, 115 kg K₂O per ha) (De Schaepmeester 2021). Thus, nutrient management is crucial to produce large quantities of bark. The cost of synthetic fertilizer is high in the eastern DRC. Because of this high cost, farmers prefer organic fertilizers (Hameed and Sawicka 2017), moreover since organic fertilizers are part of the traditional ecology knowledge of local farmers across the world, and the global awareness of the negative impacts of synthetic fertilizers. Based on our findings, the majority of the farmers in the study areas classified their soil fertility as good to average and they did therefore not use any synthetic fertilizer. The other reason for the low use of synthetic fertilizers is the lack of knowledge and information by the end users, because the majority of the farmers have received limited agricultural training according to the response of the farmers during the field survey.

Concerning plant spacing, 1 × 1 m is the most commonly used spacing in Cinchona production across the groupements. Orwa et al. (2009) also reported that for planting of Cinchona trees, a spacing of 1 × 1 m is recommended to stop soil erosion at higher altitudes. Disease and insect attacks are also the important problems affecting Cinchona production. Linear canker is the most important problem across the study areas, followed by root rot. Insect attacks are the most important problem only at Baswagha. Perennials such as Cinchona plants are often more attacked by diseases than the annual plants (De Schaepmeester 2021). Regarding tree species, C. calisaya is the most preferred and commonly grown tree species among farmers across the groupements, followed by C. pubescens, due to its higher quinine content. Pratiwi et al. (2018) also reported that C. calisaya is one of the Cinchona species that has a high (4–13%) quinine content. However, a considerable variation in content and composition of alkaloids is found between and within species, and the total content of the four major alkaloids appear to be correlated with phylogeny (Maldonado et al. 2017). The NMDS result also indicates that environmental variables influenced the production of Cinchona at Baswagha. This is due to the fact that Cinchona producers are looking for disease-free areas to expand their production and because it is also an area less troubled by conflicts (Boa 2015).

The main contribution of this work is to improve our insights about the local supply chain of Cinchona, and specifically how farm organisation relates to the production of Cinchona. Our study showed that:

• the majority of the smallholder farmers allocated land for Cinchona production, mostly in a monoculture cultivation system, using in vivo propagation, 1 × 1 m spacing, their own seeds and other smallholder farmers’ seeds;
• Cinchona calisaya is the preferred species by the farmers and is grown alone or in combination with other Cinchona species;
• Cassava and Eucalyptus are highly associated with Cinchona plantations;
• most of the farmers (> 62%) did not use any fertilizer;
• Linear canker and insect attacks are the most reported biotic problems;
• farmers in Cinchona growing areas in the eastern DRC have been able to produce Cinchona over the years with minimum input and advice from agricultural consultants.

Therefore, for sustainable production of Cinchona, attention should be given to facilitating a reliable source of inputs, in general, and improved germplasm and use of integrated soil fertility management practices at Ngweshe and Rubenga. Similarly, integrated pest management practices should be used for controlling disease at Kabare, Ngweshe, Ntambuka, and Rubenga, and insects at Baswagha. Finally, DRC contributes to ca 55% of the global quinine production compared to other Cinchona-producing countries, despite a relatively low Cinchona productivity.

This study was supported by VLIR-OUS and the NASCERE project. We thank Cinchona growers in the North and South Kivu provinces for allowing us to work in their Cinchona plots, and the local and regional administrations for providing all the necessary permissions during data collection.