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Multifaceted but understudied potential impacts of alien coffee on tropical forest regeneration

Published online by Cambridge University Press:  15 September 2026

Abhirami Chethana Open the ORCID record for Abhirami Chethana [Opens in a new window] ,
Rohit Naniwadekar  and
Anand M. Osuri
Abhirami Chethana*
Affiliation:
Manipal Academy of Higher Education, India Nature Conservation Foundation, India
Rohit Naniwadekar
Affiliation:
Nature Conservation Foundation, India
Anand M. Osuri
Affiliation:
Nature Conservation Foundation, India
*
Corresponding author: Abhirami Chethana; Email: abhirami.cdsmpl2021@learner.manipal.edu
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Abstract

Coffee is among the most highly traded agricultural commodities and cultivated across some of Earth’s most biodiverse tropical regions. The conservation literature recognizes coffee farms as potential refuges for biodiversity in landscapes where they have replaced and fragmented natural tropical forests. By contrast, little is known about whether and how coffee impacts native plant communities beyond active farms, as alien species persisting in secondary forests following discontinuation of cultivation and potential invaders into surrounding remnant forests. Here, we explore the literature on coffee in particular and alien plant species in general to identify potential impacts of alien coffee on native plant regeneration. As a prolific, shade-tolerant woody species, alien coffee can theoretically influence native species pollination, dispersal, seed germination, and establishment over prolonged periods, but these effects and consequences for plant community dynamics remain largely untested. Key knowledge gaps include the direction and strength of alien coffee effects on native plant regeneration and how they vary with regeneration stage, native species traits, environmental conditions, coffee species, and forest type (secondary forest vs. invaded remnant). Investigating these gaps can enrich the discourse on coffee and conservation, guide restoration in coffee-occupied forests, and advance the relatively underdeveloped field of shade-tolerant alien species ecology.

Keywords

Abandoned agriculturealien invasive plantsCoffeaconservationhuman-modified landscapesplant–animal interactionssecondary successiontropical forest

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Insight
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Journal of Tropical Ecology , Volume 42 , 2026 , e29
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Copyright
© The Author(s), 2026. Published by Cambridge University Press

Introduction

Coffee is among the most highly traded agricultural commodities, with over 11 Mt green bean produced annually and global cultivated extent exceeding 120,000 km2 (FAO 2025). Coffee cultivation has greatly expanded across the tropics over the past seven decades, most notably in Asia and Africa, and is now present in nearly every tropical biodiversity hotspot (FAO 2025; Hardner and Rice Reference Hardner and Rice2002; Figure 1). This congruence with regions of exceptional and threatened biodiversity underscores the significance of coffee for conservation, both as a threat contributing to the transformation of forested landscapes into production mosaics and as a potential ally offering refuges for biodiversity in these transformed mosaics (Manson et al. Reference Manson, Nekaris, Nijman and Campera2024; Perfecto et al. Reference Perfecto, Rice, Greenberg and Van der Voort1996). While this topic has inspired considerable research and vibrant discourse (De Beenhouwer et al. Reference De Beenhouwer, Aerts and Honnay2013; Garcia et al. Reference Garcia, Bhagwat, Ghazoul, Nath, Nanaya, Kushalappa, Raghuramulu, Nasi and Vaast2010; Perfecto et al. Reference Perfecto, Vandermeer and Philpott2014), certain aspects of the interplay between coffee cultivation and the conservation of tropical biodiversity and ecosystems remain underrecognized and poorly understood.

Figure 1.

(a) The geographic extent of coffee cultivation has increased greatly since the 1960s, particularly in Asia and Africa, and (b) coffee is now cultivated within nearly every global biodiversity hotspot across the tropics (Data source: Al-Abdulkader et al. Reference Al-Abdulkader, Al-Namazi, AlTurki, Al-Khuraish and Al-Dakhil2018; FAO 2025; Ovalle et al. Reference Ovalle, Läderach, Bunn, Obersteiner and Schroth2015).

Graphs depict coffee cultivation areas and biodiversity hotspots.

A lot of conservation research has focused on examining the potential of coffee farms to serve as refuges for biodiversity in production landscapes (Alvarez-Alvarez et al. Reference Alvarez-Alvarez, Almazán-Núñez, González-García, Brito-Millán, Méndez-Bahena and García-Ibáñez2021; Bohada-Murillo et al. Reference Bohada-Murillo, Castaño-Villa and Fontúrbel2020; Caudill et al. Reference Caudill, DeClerck and Husband2015; Jha and Vandermeer Reference Jha and Vandermeer2010; Rojas et al. Reference Rojas, Godoy, Hanson, Kleinn and Hilje2001). Coffee is traditionally cultivated under a canopy of diverse shade trees, and many studies show that tree-shaded coffee farms are substantially more hospitable for a large proportion of native forest-affiliated biodiversity compared to other production systems (Perfecto et al. Reference Perfecto, Rice, Greenberg and Van der Voort1996; Tylianakis et al. Reference Tylianakis, Klein and Tscharntke2005). A growing number of studies raise concerns about the erosion of biodiversity friendliness due to the intensification of coffee farm management practices, prompting conservation programmes to focus on interventions to revive less intensive traditional farming practices (Jha et al. Reference Jha, Bacon, Philpott, Ernesto Méndez, Läderach and Rice2014; Philpott et al. Reference Philpott, Arendt, Armbrecht, Bichier, Diestch, Gordon, Greenberg, Perfecto, Reynoso-Santos, Soto-Pinto, Tejeda-Cruz, Williams-Linera, Valenzuela and Zolotoff2008; Wynter et al. Reference Wynter, Milner-Gulland and Poore2025). Meanwhile, many coffeeproducing mosaic landscapes also feature patches of natural tropical forests, such as primary and degraded forest remnants on protected and uncultivated lands (Osuri et al. Reference Osuri, Kasinathan, Raman and Mudappa2024; Toledo and Moguel Reference Toledo and Moguel2012), and secondary forests growing on lands discontinued from coffee cultivation (Marcano-Vega et al. Reference Marcano-Vega, Mitchell Aide and Báez2002; Raymundo et al. Reference Raymundo, Prado-Junior, De Oliveira-Neto, Santana, Do Vale, Jacobson, De Oliveira and Carvalho2018; Rivera and Aide Reference Rivera and Aide1998). Previous studies have highlighted the disproportionate importance of such forests for sustaining biodiversity in production landscapes (Anand et al. Reference Anand, Krishnaswamy, Kumar and Bali2010; Arroyo-Rodríguez et al. Reference Arroyo-Rodríguez, Fahrig, Tabarelli, Watling, Tischendorf, Benchimol, Cazetta, Faria, Leal, Melo, Morante-Filho, Santos, Arasa-Gisbert, Arce-Peña, Cervantes-López, Cudney-Valenzuela, Galán-Acedo, San-José, Vieira, Slik, Nowakowski and Tscharntke2020), and their contribution to flows of biodiversity and key ecosystem services such as crop pollination, pest regulation, and soil nutrient recycling into nearby coffee farms (Geeraert et al. Reference Geeraert, Aerts, Berecha, Daba, De Fruyt, D’hollander, Helsen, Stynen and Honnay2020; Karp et al. Reference Karp, Mendenhall, Sandí, Chaumont, Ehrlich, Hadly and Daily2013; Ricketts et al. Reference Ricketts, Daily, Ehrlich and Michener2004; Velmourougane Reference Velmourougane2017). By contrast, flows in the opposite direction—i.e., impacts of coffee cultivation on forests in surrounding landscapes—have received far less attention. Notably, key gaps remain in our understanding of how alien wild populations of commercial coffee species such as Coffea arabica (arabica coffee), C. canephora (robusta coffee) and C. liberica (liberica coffee) affect the structure and dynamics of tropical forests in coffee producing landscapes.

Beyond their native distributions in Africa, commercial coffee species (hereafter collectively referred to as coffee) can enter natural forest plant communities through two pathways. One is the continued reproduction and natural regeneration of coffee in secondary forests growing on lands where it was previously cultivated, as evidenced by several studies from the Americas (Garcia-Montiel and Scatena Reference Garcia-Montiel and Scatena1994; Marcano-Vega et al. Reference Marcano-Vega, Mitchell Aide and Báez2002; Raymundo et al. Reference Raymundo, Prado-Junior, De Oliveira-Neto, Santana, Do Vale, Jacobson, De Oliveira and Carvalho2018; Rivera and Aide Reference Rivera and Aide1998; Thompson et al. Reference Thompson, Brokaw, Zimmerman, Waide, Everham, Lodge, Taylor, García-Montiel and Fluet2002); Figure 2a). Another pathway for coffee to enter forests is through dispersal and colonization. Coffee species produce fleshy fruits that are consumed by a variety of wild mammal frugivores and seed dispersers (Bal et al. Reference Bal, Nath, Nanaya, Kushalappa and Garcia2011; Mudappa et al. Reference Mudappa, Kumar and Chellam2010; Singh et al. Reference Singh, Kumara, Kumar and Sharma2002; Subrata and Syahbudin Reference Subrata and Syahbudin2016). Studies from India’s Western Ghats provide evidence of commercial coffee species invading forests hundreds of metres from active or discontinued cultivation areas (Joshi et al. Reference Joshi, Mudappa and Raman2009; Muthuramkumar et al. Reference Muthuramkumar, Ayyappan, Parthasarathy, Mudappa, Raman, Selwyn and Pragasan2006; Figure 2b), and coffee has been labelled an alien invasive species in parts of the Pacific Islands and Australia (Lymburner et al. Reference Lymburner, Handley and Handley2006; Meyer Reference Meyer2000; US Fish and Wildlife Service 2015). Studies from discontinued coffee secondary forests and coffee-invaded forests suggest that alien coffee can perform well across a range of site conditions and dominate forest mid- and understory plant communities for at least several decades (Pascarella et al. Reference Pascarella, Aide, Serrano and Zimmerman2000; Raymundo et al. Reference Raymundo, Prado-Junior, De Oliveira-Neto, Santana, Do Vale, Jacobson, De Oliveira and Carvalho2018). Yet, the processes through which alien coffee can influence the structure, composition, and dynamics of forest plant communities remain unexplored. Addressing this gap can improve our mechanistic understanding of the ecological impacts of alien coffee and facilitate better conservation, management, and restoration of forests in coffee-producing landscapes, with the potential to offer wider insights into the generally understudied ecological impacts of shade-tolerant alien invasive species.

Figure 2.

(a) Secondary tropical forest 30–40 years after discontinuation of Coffea canephora cultivation (image credit: Namitha Kanallimath) and (b) invasive C. canephora in a rainforest remnant adjoining active coffee cultivation in the Western Ghats, India (image credit: Kalyan Varma). Coffee is the dominant understory plant in both examples. White arrows highlight representative coffee individuals.

Two photos of tropical forest areas with coffee plants highlighted by white arrows.

Based on an exploratory literature review, we conceptually examine potential impacts of alien coffee on multiple stages of native plant reproduction and regeneration in tropical forests. We consider potential impacts on native species pollination, frugivory and seed dispersal, seed germination and seedling establishment (Wang and Smith Reference Wang and Smith2002), which are early life processes that are known to strongly influence tropical forest tree community dynamics (Green et al. Reference Green, Harms and Connell2014). We describe broad theoretical expectations for likely impacts of alien species on native species during each process and develop those expectations in the context of alien coffee, drawing from the literature on coffee where available, and relevant parallels from the literature on other alien and invasive species. In the process, we identify gaps in conceptual understanding and empirical evidence of how alien coffee influences forest plant community dynamics, as a step towards advancing basic and applied research on the ecology, management, and restoration of tropical forests in coffee-producing landscapes.

Alien coffee and forest dynamics

Pollination

Alien plant species can affect pollination—and ultimately fruit production—of native plant species by augmenting floral resources, increasing local- and landscape-level pollinator abundances, and modifying plant-pollinator networks (Bjerknes et al. Reference Bjerknes, Totland, Hegland and Nielsen2007). Aliens can have both positive (facilitative) and negative (competitive) effects on native plant pollination (Traveset and Richardson Reference Traveset and Richardson2006). Alien-induced increases in pollinator abundances could facilitate increased pollinator visits to native flowers, as seen in studies on alien Carpobrotus sp. (Bartomeus et al. Reference Bartomeus, Vilà and Santamaría2008; Moragues and Traveset Reference Moragues and Traveset2005). Contrarily, studies on Opuntia stricta (Bartomeus et al. Reference Bartomeus, Vilà and Santamaría2008) and Chromolaena odorata (Ghazoul Reference Ghazoul2004) provide examples of aliens outcompeting native flowers for pollinators. Other pollination-based pathways for alien impacts on native species include heterospecific pollen interference, in which alien species pollen deposited on native flower stigmas can impede their fertilization (Brown et al. Reference Brown, Mitchell and Graham2002; Morales and Traveset Reference Morales and Traveset2008), and alien species hybridization with closely related native species (Abbott Reference Abbott1992; Bleeker et al. Reference Bleeker, Schmitz and Ristow2007; Vilà et al. Reference Vilà, Weber, D’Antonio, Vil??, Weber and D’Antonio2000). Alien species are more likely to affect pollination and fruit production of closely related native species that they flower coincidentally with (Levin and Anderson Reference Levin and Anderson1970), as illustrated by studies on the effects of alien Senecio inaequidens on the reproductive success of native S. jacobaea (Vanparys et al. Reference Vanparys, Meerts and Jacquemart2008).

Coffee species are known to exhibit synchronous mass flowering that can generate substantial floral resources and attract a wide range of insect pollinators, including honey bees, stingless bees, and carpenter bees (Alvim Reference Alvim de and Halevy2019; Ngo et al. Reference Ngo, Mojica and Packer2011; Schmitt and Perfecto Reference Schmitt and Perfecto2020; Figure 3a). On active coffee farms mass flowering is known to be associated with increased pollinator abundances (Prado et al. Reference Prado, Collazo, Marand and Irwin2021). Furthermore, there is some evidence that flowering coffee can contribute substantially to the diets of wild pollinators, and periodically potentially disrupt native plant-pollinator networks. A Brazilian study recorded arabica coffee pollen in over 50% of solitary bee nests in forests surrounding coffee farms, with coffee comprising over 50% of the pollen in those nests (Pereira Machado et al. Reference Pereira Machado, Baronio, Soares Novaes, Ollerton, Wolowski Torres, Natalina Silva Lopes and Rech2024). Similar effects are plausibly associated with alien coffee in forest understories, particularly in secondary forests that harbour formerly cultivated mature coffee trees, and under more open canopies which are known to promote coffee flower production (Cannell Reference Cannell1975; Montoya et al. Reference Montoya, Sylvain and Umaña1961). This highlights the need for empirical research into whether alien coffee facilitates or inhibits pollination of native species and how such effects vary with species identity, forest age and condition, and landscape factors such as proximity to active farms in coffee-producing landscapes. Also needing to be investigated are the extent of heterospecific pollen interference by commercial coffee and the prevalence of their hybridization with closely related native species, including the over 100 wild Coffea species that are distributed across the Paleotropics (Guyot et al. Reference Guyot, Hamon, Couturon, Raharimalala, Rakotomalala, Lakkanna, Sabatier, Affouard and Bonnet2020).

Figure 3.

Coffee can potentially influence multiple biotic interactions that shape native plant reproduction and regeneration. (a) A native Apis cerana visiting robusta coffee flowers (image credit: K P Akilan), (b) fruiting arabica coffee, and (c) coffee seeds in civet scat (image credit: T R Shankar Raman) in discontinued coffee secondary forests and rainforest remnants in the Western Ghats.

Three photos showing coffee plants and seeds in different stages.

Frugivory and seed dispersal

Coffee fruits exhibit several attributes associated with frugivore attraction. These include prominent red berries (De Castro and Marraccini Reference De Castro and Marraccini2006; Figure 3b) with high nutrient content (Carmen et al. Reference Carmen, Lorena, Alexander, Amandio and Raúl2020; Oliveira and Franca Reference Oliveira, Franca and Preedy2015), pulp-to-seed ratios (Oliveira and Franca Reference Oliveira, Franca and Preedy2015), and a synchronous mass-fruiting habit (Aslan and Rejmanek Reference Aslan and Rejmanek2012; Raymundo et al. Reference Raymundo, Prado-Junior, De Oliveira-Neto, Santana, Do Vale, Jacobson, De Oliveira and Carvalho2018). In its introduced range, studies have documented coffee frugivory by palm civets, macaques, and elephants in Asia (Bal et al. Reference Bal, Nath, Nanaya, Kushalappa and Garcia2011; Gruezo Reference Gruezo1990; Mudappa et al. Reference Mudappa, Kumar and Chellam2010; Singh et al. Reference Singh, Kumara, Kumar and Sharma2002; Subrata and Syahbudin Reference Subrata and Syahbudin2016; Umapathy and Kumar Reference Umapathy and Kumar2000) and colobus monkeys and bats in Africa (Oryem-Origa Reference Oryem-Origa1999). Studies from Asia also show that alien coffee is among the most highly consumed fruits in both civet and macaque diets (Figure 3c). Coffee ranked among the ten most frequently consumed fruit species by the Brown palm civet (Mudappa et al. Reference Mudappa, Kumar and Chellam2010) and occurred in 100% of faecal samples of Lion-tailed macaques (Singh et al. Reference Singh, Kumara, Kumar and Sharma2002) in India’s Western Ghats. Similarly, coffee seeds were recorded in 42% of scat samples and emerged as the most frequently encountered species in civet scats in an Indonesian study (Subrata and Syahbudin Reference Subrata and Syahbudin2016). There is comparatively less evidence of frugivory on coffee in the Americas, with one study suggesting that certain rodent species could disperse coffee seeds (Sánchez-Brenes and Monge-Meza Reference Sánchez-Brenes and Monge-Meza2024).

One possible consequence of alien species attracting frugivores is the reduction in frugivore visits and seed dispersal of coincidentally fruiting native species. Alternatively, alien species could increase native species frugivory through neighbourhood effects (Sargent Reference Sargent1990), in which frugivores attracted by fruiting alien species increase visitation and frugivory on neighbouring fruiting native species. By attracting frugivores, fruiting alien species can also increase incoming seed dispersal of coincidentally fruiting native species from neighbouring patches—i.e., contagious seed dispersal (Gleditsch and Carlo Reference Gleditsch and Carlo2011; Vergara-Tabares et al. Reference Vergara-Tabares, Blendinger, Tello, Peluc and Tecco2022). Contagious seed dispersal has been previously recorded in abandoned farms of mammal-dispersed horticultural species such as avocado, mango (Jacob et al. Reference Jacob, Lechowicz and Chapman2017), jackfruit (Gomes et al. Reference Gomes, Cazetta, Bovendorp and Faria2021), and guava (Berens et al. Reference Berens, Farwig, Schaab and Böhning-Gaese2008), but its association with alien coffee remains unknown. Similar to effects at the pollination stage and with coffee fruiting declining with shade (DaMatta et al. Reference DaMatta, Ronchi, Maestri and Barros2007), alien coffee effects on native plant-frugivore networks and seed dispersal are likely to be stronger in discontinued coffee secondary forests than invaded remnants and in forests with more open canopies. Such effects might also be more prevalent in Asian and African forests, where wild mammal frugivory on alien coffee appears more prevalent than in the Americas (see references at the beginning of this section). Studies are needed to investigate the prevalence of competitive versus facilitative outcomes for native species frugivory and seed dispersal, how these effects are modified by other local and landscape factors and biogeographic differences, and implications for forest dynamics in coffee-producing landscapes.

Seed germination

Successful alien and invasive plant species typically produce large quantities of seeds (Richardson and Rejmánek Reference Richardson and Rejmánek2011) that can saturate germination niches and limit germination opportunities for native seeds. Such effects have been reported in studies on alien invasive Picea abies (Dovčiak et al. Reference Dovčiak, Hrivnák, Ujházy and Gömöry2007) and Neltuma juliflora (Shiferaw et al. Reference Shiferaw, Bekele, Demissew and Aynekulu2019). Seed germination niche saturation by alien coffee is a possibility that warrants examination, given that coffee species are associated with prolific seed production (Teketay Reference Teketay1998) and high rates of seed dispersal into forests from cultivated areas in certain regions (Joshi et al. Reference Joshi, Mudappa and Raman2009; Sinu et al. Reference Sinu, Fahira, Rajesh, Viswan, Manoj, Hariraveendra and Jose2023). Alien species also have the potential to affect seed germination and the performance of young seedlings through allelopathic effects, microclimate modification, and by altering plant-herbivore interactions; we elaborate on these in the following section, as these pathways are shared with—and possibly more influential during—processes of seedling establishment.

Seedling establishment

Alien plant species can affect the establishment of native plant seedlings through multiple pathways, including by increasing seedling competition (Gioria et al. Reference Gioria, Hulme, Richardson and Pyšek2023; Gioria and Osborne Reference Gioria and Osborne2014), introducing allelopathic effects (Orr et al. Reference Orr, Rudgers and Clay2005; Yuan et al. Reference Yuan, Li, Yu, Oduor and van Kleunen2021), modifying understory microclimates (Solfiyeni et al. Reference Solfiyeni, Syamsuardi, Chairul and Mukhtar2022), and disrupting interactions of native plants with herbivores (Harvey et al. Reference Harvey, Bukovinszky and van der Putten2010; Ssali et al. Reference Ssali, Baluku, Drileyo and Muhumuza2024) and soil microbes (Reinhart and Callaway Reference Reinhart and Callaway2006). Coffee exhibits a number of attributes that suggest its potential as an alien species to affect native species establishment through these pathways.

Coffee leaves exhibit substantial morphological plasticity and are known to sustain productivity in high- and low-light environments (Araujo et al. Reference Araujo, Dias, Moraes, Celin, Cunha, Barros and DaMatta2008). This suggests that alien coffee could compete with native seedlings across a range of site conditions, and a field study from the Western Ghats suggests that robusta coffee might compete more strongly than arabica coffee across varied site conditions (Joshi et al. Reference Joshi, Mudappa and Raman2009). Coffee leaves, stems, and seeds also contain allelopathic compounds such as caffeine and theobromine that are known to reduce germination and recruitment in agricultural crops (Chou and Waller Reference Chou and Waller1980; Da Rosa et al. Reference Da Rosa, De Oliveira Vilela, Alves, Cardoso, Vieira, Ferreira and Da Silva2025; Peneva Reference Peneva2007). Previous research on the alien species Rhamnus cathartica, Eucalyptus camaldulensis, and Lolium arundinaceum suggests that allelopathic effects can impact multiple early life stages of native woody species (Orr et al. Reference Orr, Rudgers and Clay2005; Ruwanza et al. Reference Ruwanza, Gaertner, Esler and Richardson2015; Warren et al. Reference Warren, Labatore and Candeias2017). Whether alien coffee exerts similar effects on native tree species remains to be examined.

Alien coffee recruits often form dense stands (US Fish and Wildlife Service 2015), attaining densities of 4,900 stems ha⁻1 in secondary forests establishing in discontinued coffee farms in Puerto Rico (Pascarella et al. Reference Pascarella, Aide, Serrano and Zimmerman2000) and 11,475 stems ha⁻1 in coffee-invaded rainforest fragments in India’s Western Ghats (Joshi et al. Reference Joshi, Mudappa and Raman2009). Studies on other alien species (e.g., Bellucia pentamera) illustrate that such high densities can alter key microclimatic factors that influence native species regeneration (Solfiyeni et al. Reference Solfiyeni, Syamsuardi, Chairul and Mukhtar2022). In secondary forests on discontinued coffee farms, preexisting mature coffee trees could reduce light not just for native seedlings but also for small trees, as seen with other alien tree species such as Psidium cattleyanum (Florens et al. Reference Florens, Baider, Seegoolam, Zmanay and Strasberg2017). Research on other alien species that reduce understory light (e.g., Lantana camara) suggests context-dependent effects on native species establishment ranging from negative effects on the establishment of shade-intolerant species (Standish et al. Reference Standish, Robertson and Williams2001; Sundaram and Hiremath Reference Sundaram and Hiremath2012) to neutral or positive effects on shade-tolerant species (Gooden et al. Reference Gooden, French and Turner2009). In the case of alien coffee, such effects could also be modulated by forest age, canopy intactness, and proximity to seed sources in active coffee farms.

Another potential pathway for alien species to influence forest seedling dynamics is the alteration of plant–herbivore interactions. In the case of coffee, this can include the direct spillover from coffee to closely related native species of non-native insect herbivores such as the coffee berry moth in Mauritius (Kaiser et al. Reference Kaiser, Hansen and Müller2008) and black tree borer beetle in the Pacific Islands (Nishida and Evenhuis Reference Nishida and Evenhuis2000). Additionally, alien species possessing chemical defences can modify herbivore visitation and damage to native species in contrasting ways. Chemically defended alien species could extend protection to less defended neighbouring native seedlings by deterring herbivores from patches, or increase the targeting of neighbouring native seedlings by herbivores—associational resistance or associational susceptibility, respectively (Barbosa et al. Reference Barbosa, Hines, Kaplan, Martinson, Szczepaniec and Szendrei2009). Coffee seeds and seedlings are known to possess chemical defences, such as diterpenes (Chou and Waller Reference Chou and Waller1980; Da Rosa et al. Reference Da Rosa, De Oliveira Vilela, Alves, Cardoso, Vieira, Ferreira and Da Silva2025) but the impacts of alien coffee on native plant–herbivore interactions remain unclear (Niranjana et al. Reference Niranjana, Krishnan, Murali, Raman, Mudappa, Sankaran and Kohli2025).

Finally, alien species could modify soil and foliar microbiota, with the possibility of both negative and positive consequences for native plant regeneration (Reinhart and Callaway Reference Reinhart and Callaway2006; Rout and Callaway Reference Rout and Callaway2012). In the case of coffee, long-term cultivation is known to reduce beneficial soil microbes and promote the accumulation of soil pathogens (Zhao et al. Reference Zhao, Xiong, Xing, Sun, Lin and Dong2018), and reports exist of coffee-associated fungal pathogens spilling over from active farms into nearby forests and infecting closely related species (Lackmann Reference Lackmann2025). Conversely, coffee seedlings appear to be highly dependent on mycorrhizal fungi (Vaast et al. Reference Vaast, Zasoski and Bledsoe1997), and coffee rhizospheres can support diverse mycorrhizal communities and beneficial fungi such as Trichoderma (Arias et al. Reference Arias, Heredia-Abarca, Sosa and Fuentes-Ramírez2012; Cogo et al. Reference Cogo, Guimarães, Rojas, Saggin Júnior, Siqueira and Carneiro2017; De Beenhouwer et al. Reference De Beenhouwer, Muleta, Peeters, Van Geel, Lievens and Honnay2015). Such microbial associations could indirectly benefit native seedlings by enhancing pathogen suppression and nutrient uptake through mycorrhizal associations (Ahedo-Quero et al. Reference Ahedo-Quero, Aquino-Bolanos, Ortiz-Hernandez and Garcia-Sanchez2024; Okoth et al. Reference Okoth, Okoth, Wachira and Roimen2009). All the microbe-mediated effects described above could plausibly persist and affect native seedlings in discontinued coffee secondary forests and coffee-invaded remnants, but remain largely untested.

Collectively, there appear to be several plausible pathways for alien coffee to alter the performance and establishment of native seedlings and young trees, with effects likely to vary with forest age, condition, and type (discontinued coffee secondary forest or invaded remnant), coffee and native species identity, and landscape factors, including proximity to active cultivation.

Looking ahead

In summary, threads of evidence drawn from the literature on coffee and other alien species suggest that alien coffee has the potential to alter natural regeneration in tropical forests by modifying growing environments, competing with native plants, and disrupting trophic interactions between native plants and pollinators, frugivorous seed dispersers, herbivores, and soil microbes over decadal timescales or longer (Figure 4). Interestingly, alien coffee can hypothetically drive both favourable and detrimental outcomes for native species during multiple processes and stages of reproduction and establishment. This underscores the need—and a variety of interesting directions—for fundamental and applied research on the ecology, impacts, and management of this shade-tolerant alien invasive species in tropical forests. Key directions include (1) investigating the strength and ecological significance of alien coffee impacts at different stages of native plant regeneration, including through comparative experimental approaches such as thinning or clearing of invasive coffee stands; (2) identifying environmental conditions and plant functional traits associated with positive versus negative impacts of alien coffee at different stages, and consequences for floristic trajectories, (3) assessing forest degradation by alien coffee and testing coffee removal and other interventions to guide the design of cost-effective restoration strategies, and (4) examining whether and how all of the above differ between (a) commercial coffee species, (b) secondary forests with discontinued coffee cultivation and previously uncultivated forest remnants invaded by alien coffee, and (c) coffee-producing regions with contrasting biogeographic and evolutionary histories. Finally, while we have focused on the standalone effects of alien coffee, forests occupied by coffee often harbour other alien species too (Joshi et al. Reference Joshi, Mudappa and Raman2015). Studies from other systems suggest that co-occurring alien species can modulate one another’s effects on native species and ecosystems (Lenda et al. Reference Lenda, Skórka, Knops, Żmihorski, Gaj, Moroń, Woyciechowski and Tryjanowski2019) and highlight the relevance of investigating such interactive effects in coffee-occupied forests.

Figure 4.

Alien coffee has the potential to alter multiple key processes associated with forest regeneration including pollination, frugivory and seed dispersal, seed germination, and seedling establishment. The potential impacts of alien coffee theoretically span the spectrum from facilitation to inhibition of native species regeneration in remnant and secondary forests in coffee-growing landscapes, and represent abundant opportunities for various avenues of basic and applied research.

Diagram illustrating the impact of alien coffee on forest regeneration processes.

An improved understanding of the impacts of alien coffee on the structure and dynamics of secondary and remnant tropical forests can add an important dimension to the discourse on coffee and conservation. This dimension is important because such forests play a pivotal role in sustaining biodiversity and ecosystem functions in production landscapes (Anand et al. Reference Anand, Krishnaswamy, Kumar and Bali2010; Melo et al. Reference Melo, Arroyo-Rodríguez, Fahrig, Martínez-Ramos and Tabarelli2013; Tabarelli et al. Reference Tabarelli, Santos, Arroyo-Rodríguez and De Melo2012), and are present in many coffee-producing biodiversity hotspots (Hardner and Rice Reference Hardner and Rice2002). Moreover, market dynamics and climate change are redefining coffee cultivation geographies, with likely expansion into new forest landscapes in some regions and discontinuation of cultivation with possible opportunities for restoration in others (Magrach and Ghazoul Reference Magrach and Ghazoul2015). A greater recognition and understanding of this dimension could also encourage and enable sustainable and biodiversity-friendly agriculture programmes to adopt more holistic approaches that consider and address impacts beyond farms, including the conservation and restoration of secondary and remnant forests, in coffee-producing landscapes.

Acknowledgements

We are grateful to M Sankaran, D Mudappa, M Ghosh-Harihar, V S Kumar, G Ramaswami, and A Krishnan for discussions that contributed to this manuscript. We thank M R Bharath, R Mandal, T R Shankar Raman, K Varma, N C Kanallimath and K P Akilan for help with the figures and illustrations. We also thank Sci-Hub for enabling access to relevant literature. We sincerely acknowledge coffee farmers, landowners, and the Karnataka Forest Department for support, permits, and long-term research and restoration partnerships.

Financial support

We thank Rohini Nilekani Philanthropies for PhD fellowship and research grants to AC through Nature Conservation Foundation. We acknowledge funding support from The Rufford Foundation, Cholamandalam Investment and Finance Company, Godrej Consumer Products Ltd., and Arvind Datar.

Competing interests

The authors declare none.

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Figure 1. (a) The geographic extent of coffee cultivation has increased greatly since the 1960s, particularly in Asia and Africa, and (b) coffee is now cultivated within nearly every global biodiversity hotspot across the tropics (Data source: Al-Abdulkader et al.2018; FAO 2025; Ovalle et al.2015).

Figure 1

Figure 2. (a) Secondary tropical forest 30–40 years after discontinuation of Coffea canephora cultivation (image credit: Namitha Kanallimath) and (b) invasive C. canephora in a rainforest remnant adjoining active coffee cultivation in the Western Ghats, India (image credit: Kalyan Varma). Coffee is the dominant understory plant in both examples. White arrows highlight representative coffee individuals.

Figure 2

Figure 3. Coffee can potentially influence multiple biotic interactions that shape native plant reproduction and regeneration. (a) A native Apis cerana visiting robusta coffee flowers (image credit: K P Akilan), (b) fruiting arabica coffee, and (c) coffee seeds in civet scat (image credit: T R Shankar Raman) in discontinued coffee secondary forests and rainforest remnants in the Western Ghats.

Figure 3

Figure 4. Alien coffee has the potential to alter multiple key processes associated with forest regeneration including pollination, frugivory and seed dispersal, seed germination, and seedling establishment. The potential impacts of alien coffee theoretically span the spectrum from facilitation to inhibition of native species regeneration in remnant and secondary forests in coffee-growing landscapes, and represent abundant opportunities for various avenues of basic and applied research.