Erythrina A Versatile Genus For Agroforestry Systems

Erythrina (Leguminosae: Papilionoideae): A Versatile Genus for Agroforestry Systems in the Tropics Ricardo 0. Russo

ABSTRACT. The genus Erythrina is of special interest in the development of agroforestry systems because of its adaptability to several uses (e.g., live posts for fences, shade trees for perennial crops such as coffee and cacao, forage for livestock, and others). Rapid plant growth, high biomass production, easy propagation from cuttings, ability to withstand regular pruning plus subsequent rapid sprouting and development of strong shoots, are characteristics that make Elythrina an attractive genus to be used in agroforestry. The abundant nodulation in the rootlets and its potential as a nitrogen fixer, open interesting possibilities for establishing plantations on low fertility soils and/or restoring these soils. Some of the most common uses of Erythrina species are discussed in this review related to specific agroforestry applications. Ricardo 0. Russo is affiliated with Yale Universitv. School of Forestw and Environmental Studies, 370 Prospect Street, New ~ a v & CT , 06511; The author pratefully appreciates the cooperation and support received from all the faculty and;taff of ihe'fropical ~~riculiural.~enter for~esearchand Training (CATIE), Turrialba, Costa Rica, during his stay at the ,Center (1981-1986). Acknowledgment is also extended to the International Development Research Center (IDRC) from Canada for the financial support received through the Eythrina Project (1983-1986) and to the personnel of INFORAT at CATIE, Turrialba, Costa Rica, where the main body of references were obtained. The author also appreciates the cooperation and suggestions given by Dr. John C. Gordon, Dean of the Yale School of Forestry and Environmental Studies, during the preparation of this manuscript. Journal of Sustainable Agriculture, Vol. l(2) 1990 O 1991 by The Haworth Press, Inc. All rights reserved.

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INTRODUCTION Currently, agroforestry is a rational alternative for land use. It contributes to food, fiber and wood production through a simple and generally low-cost technology. This practice combines trees with crops or pastures in a simultaneous or alternate association, with the objective of maximizing production per unit area, under sustainable conditions (Combe and Budowski, 1979). In a Workshop on Agroforestry held at CATIE, Turrialba, Costa Rica, March 1979 the participants reached the conclusion that . . "When agroforestry systems are utilized, many elements enter into consideration such as: more efficient use of space, provision of the basic necessities of the rural populations, improvement of the quality of life in agricultural communities, avoidance of a reduction in the productive capacity of the resources involved and a reconciliation of the short term interests of the farmers with the long term interests of countries or regions" (Workshop Agro-Forestry Systems, 1979). Nitrogen fixing trees (NFT) play an important role in agroforestry, because of their utility and their potential for adding available nitrogen to agroforestry systems . Erythrina spp. are NFT frequently used in agroforestry systems.

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Description of the Genus Etythrina The genus Erythrina L., belongs taxonomically to the subfamily Papilionoideae of the Leguminosae. However, in the literature, and according to botanists that separate the legumes into three families it also appears as belonging to the Papilionaceae or Fabaceae family (Krukoff, 1939). The genus contains over one hundred species (Krukoff and Barneby, 1974), distributed throughout the tropics and subtropics, in a wide variety of habitats (Neill, 1984) in both the Old and the New World. There are 26 species in tropical Africa, five in Southern Africa, twelve in Continental Asia and the Pacific Islands, and two in Australia. In the New World there are 27 species and three subspecies in Mexico, 25 in Central America and nine in the Caribbean (Krukoff, 1982). Lackey (1981) places Etythrina in the subtribe Erythrininae of

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the tribe Phaseolae (Fabaceae-Faboideae), with the following comment: "The relationship of this genus to the remainder of the Papilionoideae is an absolute mystery. The genus would have long ago accomodated outside the Phaseoleae had not the foliage suggested this tribe. The genus certainly deserves separate tribal recognition; however, such recognition would only compound problemd of generating other artificial taxonomic groups to accomodate the remainder Erythrininae, and in no way would clarify the puzzling status of Erythrina, already a widely recognized difficulty." Erythrina is grouped with eight other genera in the subtribe Erythrininae (Strogylodon, Mucuna, Butea, SpatholobuG, Apios, Cochlianthus, Rhodopis, and Neurudolphia). But the differences between these genera and Erythrina are large and for that reason, Raven (1982) proposed that it could be segregated as a monogeneric tribe. Erythrina is subdivided into four subgenera: Micropteryx, Erythrina, Chirocalyx, and Erythraster, and further into 26 sections (Krukoff, 1982). Most species are trees or shrubs, deciduous, with leaves odd-pinnate, trifoliate, alternate, with glandular stipels on the petiole (Cook, 1901; Dwyer and D'Arcy, 1980). The stem and branches are usually armed with stout spines, and sometimes spines are present also on the rachis. Flowers occur in clusters, in general located near the apical ends, in lateral inflorescenses, although the genus exhibits a great diversity in floral structure and inflorescence orientation (Neill, 1984). Almost all Erythrina species have reddish, scarlet, or orange flowers, produce nectars and are adapted to pollination by avian pollinators, passerines and hummingbirds (Feinsinger et al., 1979; Neill, 1984). The fruit is a slender twovalved pod, more or less moniliform, generally dehiscent, containing several seeds. The seeds contain alkaloids (Folkers and Unna, 1939) and are used medicinally (Duke, 1972). According to Lewis (1974) the species of this genus have 21 pairs of chromosomes (2n = 42). Erythrina species have been known as having curare-like alkaloids (Folkers and Unna, 1939). The genus Erythrina includes species that are known to bear root nodules (Allen and Allen, 1981). These nodules are formed after the infection of the roots by compatible strains of the soil bacteria Rhizobium,

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and provide Erythrina with the ability to fix atmospheric nitrogen. Biological nitrogen fixation (BNF), is a highly desirable trait in any plant as it allows self sufficiency in nitrogen supply. Furthermore, Erythrina's BNF capability possibly contributes to its rapid growth and to success in coppicing. Capability for nitrate reduction is another remarkable aspect of Erythrina. It possesses a reduction system with a high activity and a low affinity for nitrate reductase, thus differing significantly from other higher plants (Stewart and Orebamjo, 1979; Orebamjo, Porteous and Stewart, 1982). All of the Erythrina species studied had in vivo activities of nitrate reductase in excess of 100 micromole N02hourIg fresh weight, and the enzyme was found to use equally well both NADH and NADPH, as electron donors. The above rates are 10-100 times those reported for other angiosperms and nitrate reductase from angiosperms that preferentially use NADH rather than NADPH as the electron donor (Orebamjo et al., 1982). This unusual nitrate reducing system appears to be restricted to the genus Erythrina and may be of taxonomic importance. The leaves of various species of Erythrina are commonly used for fodder. It is a common sight to see people pruning the branches along the living fences mainly in some Central American countries. In some cases the flowers are eaten by people, cooked in soups and salads (Martin and Ruberte, 1975).

MAIN SPECIES USED IN AGROFORESTRY Etythrina poeppigiana (Walpers) O.F. Cook Its natural distribution ranges from Bolivia to Panama, although it has proven to be well adapted in other tropical areas where it has become naturalized (Raven, 1974). Such areas include Central America, the Caribbean, Africa, and Malaysia, where it was introduced as shade for coffee and cacao (National Academy of Sciences, 1979). The tree is found throughout the lowlands and middle elevations in the tropical zones with medium to high rainfall (1,5003,000 mm/year and more) with a dry season of 0-6 months. Altitude incosta Rica ranges from sea level to about 1,400 meters (Borchert, 1980); however, in Colombia and Venezuela trees have been

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observed at or slightly above 1,900 meters. This species has long been known in agroforestry. Early in this century Cook (1901) reported its use as a shade tree in coffee culture in Puerto Rico. It is known with different common names in different countries such as "por6 gigante" in Costa Rica, "pito extranjero" in Guatemala, "clmbulo" or "barbatusco" in Colombia, "bucare" or "cachimbo" in Venezuela, "amasisa" in Peru, and, usually known as "coral tree" or "immortelle" in English (Cook and Collins, 1903; Stanley and Steyermark, 1947; Holdridge and Poveda, 1975). Evidence for benefits of Eythrina as opposed to a non-legume tree Cordia alliodora for shade of cacao was reported in Turrialba, Costa Rica. Under Erythrina, cacao yields were, on average, 46% greater than under Cordia during the first four years of the study (Enriquez,l983) and 23% over a total of seven years of data (Heuveldop et al., 1988). Litterfall data from this study (Alpizar et al., 1983; 1986; Heuveldop et al., 1988) indicates that the rates of cycling for calcium, magnesium and particularly nitrogen through the cacao litter pathway are greater under Eythrina than under Cordia. Nitrogen fixation (NF) has been little investigated. Escalante, Herrera and Aranguren (1984) and Lindblad and Russo (1986) found NF to be around 12-40 kg/ha/year when planted for shade in coffee or cacao plantations. The tree is also a good source of green manure; for instance, biomass production from pollarding (lopping all branches) twice a year provided almost 12 tonsiha/year (Russo sand Budowski, 1986). Initial experiences at CATIE, Turrialba, Costa Rica showed promising results for alley cropping (Figure I), which appears to offer considerable potential as a nitrogen source for annual crops, since biomass production from Eythrina was over 8,000 kglha of dry matter contained more than 3% N (Kass, Russo and Quinlan, 1983; Kass and Barrantes, 1984). E. poeppigiana has been also reported in association with grasses (Figure 2) Cynodon plectostachyus (Bronstein, 1984) and Pennisetum purpumum (Benavides, 1983, 1985; Rodriguez, 1984). In both cases, grass showed greater production with than without Eythrina. (Figure 3). Farmers usually propagate the species through large cuttings, 2.5

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meters long and 8-12 cm in diameter. Within the first month sprouts occur (Figure 4) and in just 4-6 months shade the coffee seedlings (Figure 5, 6). Rooting success varies from 70-90% (Russo, 1984). When established, total pollarding once or twice a year (Figure 7, 8) is usuqlly practiced and the branches are spread on the ground. Foliage has been fed to small animals such as rabbits and goats with good result$, h a v e s contain between 25-30% of crude protein (total N x 6,25) and are readily eaten by cattle. Digestibility varies between 50-80% being highest for the bark of young branches. Swine apparently suffer loss of hair after ingestion. Because of its fast growth, its capability to produce high amounts of biomass, its NF capability, its easy propagation by cuttings, its excellent response to pruning practices, its high content of crude protein, this tree shows a high potential for various agroforestry practices beyond use as a coffee or cacao shade tree. FIGURE 1 . Eythrina poeppigiana large cuttings planted in association with a maize crop in CATIE, Turrialba, C. Rica.

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FIGURE 2. Pollard Erythrina poeppigiana trees associated with pasture in a farm of Santa Cruz of Turrialba, Costa Rica (Photos by R. 0.Russo).

Erythrina hsca Loureim (E. glauca Willd)

Another Erythrina species mentioned by Holdridge (1955) and by Hardy (1961) is E. fissca (best known by its former name E. glouca). It is reported as originating in S.E. Asia, and it is widely planted in cocoa farms in Comalcalco, Mexico and Brazil. It also is used as shade for coffee in some farms in the Central Valley of Costa Rica (Figure 9). According to Feinsinger et al. (1979) its .natural reproduction occurs in wet soils such as those in swamps, badly drained soils or along streams. This also had been observed previously by Holdridge and Poveda (1975), who reported pure stands in fresh water swamps in the Pacific lowlands of Costa Rica. Cadima Zeballos and Alvim (1967) observed that the cacao trees found around the the E. glauca trees produced more than the cacao further away from the shade trees. They attributed such differences to the influence that this species could have on some edaphological factors related to cacao production. Santana and Cabala-Rosand (1982) also reported that in a cacao plantation under trees of this species, higher amounts of nitrogen available to cacao trees were found. They attributed this to Erythrina litter, which has a high N content. They also reported that in cacao planted under Erythrina,

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FIGURE 4 . Etythrina poeppigiana, a month after planting, sprouting vigorously in Turrialba, C. Rica.

total N inputs are higher than N removed by a harvest of 1500 kgha dried cacao beans. Erythrina bertemana Urban

Its natural distribution ranges from southern Mexico to Costa Rica in Central America, and probably to South America whether or not it is the same species as E. mbrinervia H.B.K. (Holdridge and Poveda, 1975). Its common name is "por6 de cerca" in Costa Rica, "machete" in Jamaica, "elequeme" in Nicaragua, "gallito," "pernilla de casa" in Panama, "pito" in Colombia, and "parsu" in Cuna language. The Colombian name "pito" reflects a children's use of the plant; the corolla of its flower, placed in a hollow leaf stalk, serves as a whistle (Duke, 1972). Sanchez and Russo (1985) reported it is the species most frequently (50%) used as live fence posts (Figure 10) in Costa Rica, according to results of a survey by questionnaries.

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FIGURE 5. Erythrina poeppigiana. 4-6 months after planting, in a new coffee crop in CATIE, Turrialba, C. Rica (Photos by R. 0.Russo).

Eiythrina berteroana responds to regular pruning with a great volume of large-leafed shoots in only 3 weeks to 1 month. These shoots are often used for rabbit feed and are also palatable to livestock. Goats are particularly eager to eat these shoots. Biomass production of 1 kilometer of live fence of the species varies according to pruning frequency, as presented in Figure 11. Other Species of Erythrina

Eythrina costaricensis Micheli (E. steyermarkii Krukofl: This is another usual live fence species like E. berteroana. Its leaflets are wider than 10 cm. Its common name is "por6 cimarron" or "poro de cerca." It is easily propagated by large cuttings or seeds. It is endemic to Costa Rica, and the species can be usually found in areas of abundant rainfall (above 1,500 mm). Holdridge and Poveda (1975) consider that E. chiriquensis Krukoff, E. globocalk

FIGURE 6. Etytlrrinn Poeppigiana trees after pollarding, in a coffee crop in Turrialba, C. Rica.

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FIGURE 7. A view of a recently pollard Erythrina poeppigiana tree.

Porsch, and E. steyermarkii Krukoff and Barneby could be synonyms of E. costaricensis. Eythrina cochleata Standley: This species, also known as poro, is used in living fences. It is easily distinguished from another Etythrinas because its leaflets are very shiny. Another related species used as live fence posts in Costa Rica is E. lanceolata Standley (leaflets smaller than 10 crn width). Erythrina edulis (Micheli) Triana: This is the only Erythrina species with edible seeds. All other species have poisonous seeds, that are often used in collars or necklaces. Its common name is "balli" or "basul," "cachafruto" or "poroto." The protein content of the "balb" seeds varies between 18-21% and it has similar or higher amounts of most amino-acids compared, to other leguminosae (Perez et a l . , 1979).

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FIGURE 8. A farmer chopping the Eyrhrina branches, after cutting them down (Photos by R.O.Russo).

Erythrina americantl:' This species mentioned by Martinez (1959) is common to the uplands regions of Mexico, but also grows well at sea level. Its flowers are highly prized for their flavor and are an additional source of income for the small farmer who usually sells the flowers in the local market. This author also mentions other eleven Mexican species of Erythrina: E. breviflora, E. setosa, E. leptorhiza, E. rubrinervia, E. montanal, E. lanata, E. occidentalis, E. flabellifomis, E. foldmanii, E. maicana, and E. herbacea, also found in southern United States. Elythrina lithospenna: This species is mentioned by Urquhart (1963) as a shade tree for cacao in Western Samoa. It has also been

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FIGURE 9. A view of recently pollard Evthrina ficsca trees shading a coffee plantation in Tres Rios, Costa Rica.

reported as a shade tree for arabica coffee in India (Achyuta, 1960). Like E. poeppigiana it is also pruned twice a year. E. lithosperma is usually planted before cacao seedlings are placed in the field. One of the advantages reported for this species is that there are some thornless varieties. Erythrina umbrosa: This species has been mentioned by Flye (1945) as a shade tree for coffee plantations in Brazil.

DISCUSSION The greater potential for Erythrina spp. use lies in the development of agroforestry systems. But, all tree species associated with crops in agroforestry, have advantages and disadvantages. A good place to start is to recognize or mention cases of successful agroforestry systems. A good example of success throughout the years is E. poeppigiana which is associated with the coffee crop in Costa

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FIGURE 10. An Erythrina berteroana post in a living fence in La Suiza of Turrialba, Costa Rica (Photos by R.O. Russo).

Rica. Another case is the common use of E. berteroana and E. costaricensis in live fence posts. Characteristics, Uses, and Potential

of the Genus Erythrina The following characteristics make this genus particularly attractive for use in agroforestry: (a) Members are fast growing, and rapidly produce considerable amounts of biomass rich in nitrogen; (b) It is easily propagated by cuttings; (c) It has excellent capabilities to withstand regular pruning, subsequent rapid sprouting and develop-

FIGURE 11. Production of a live fence of E~ythrinaberferoana pruned every 4, 6, and 8 months in CARE, Turrialba. Costa Rica (Calculated and redrawn from Budowski, Russo and Mora, 1985)

I

1

I

I

4 monlhs

6 months

8 months

frequency of prunlng

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ment of strong shoots; (d) Its leaves are edible by cattle and rabbits, and are rich in protein (25-30 % of crude protein content; these figures are higher than those found in the conventional protein supplements available in the market for cattle, which are usually around 18%.); (e) The roots are generally associated with the nitrogen-fixing bacteria Rhizobium, whose root-nodules have the capability to fix atmospheric nitrogen, which is a highly desirable trait in any plant as it allows self sufficiency in nitrogen supply; ( f ) Most of the species of this genus are adequate to be used in living fences. The list, of course, could be much longer. I personally interviewed many farmers, between 1982 and 1984, when working for the CATIEIIDRC-supported Erythrina Project. A high percentage of farmers agree that "poro is good," which can be interpreted as evidence that they like the genus because of its beneficial effects. We should consider whether the genus may have potential to be used more extensively in agroforestry systems in other countries, with ecological conditions similar to those where it is currently used. In Costa Rica, for instance, the use of Erythrina for shading or nursing other crops is a common agricultural practice in both coffee and cacao plantations. There is a great deal of evidence showing its value as a "natural fertilizer" supplier and nutrient cycling helper. The calculated figures show that the return of nitrogen to the soil and nutrient cycle in coffee, cacao, and also in maize, can save up to 200 kg Nlha per year. A considerable research effort in working with this genus has been done in the Tropical Agricultural Center for Research and Training (CATIE), Turrialba, Costa Rica through the Evthrina Project (Centro Agrondmico Tropical de Investigacidn y Enseiianza, 1986b). This research project supported by the International Development Research Center (IDRC) from Canada, produced a large amount of research and also compiled a substantial bibliography on the genus (Centro Agron6mico Tropical de Investigaci6n y Enseiianza, 1986a). Finally, no doubt agroforestry activities\tend to increase the level of system complexity. This makes the management of the farm more difficult. However, if professionals' in forestry and agriculture aim at the solutions of practical problems, then it is necessary to deal with the realities that the farmer faces. We cannot sacrifice

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potential benefits for fear of making the problem a more complex one.

BIBLIOGRAPHY Achyuta, R.Y.R. 1969. Shade tree for arabica coffee: Erythrina lithospenna. Indian Coffee 24(12):500-505. Allen, O.N. and A.K. Allen. 1981. Leguminosae, a source book of characteristics, uses, and nodulation. Madison, Wisconsin, USA, University of Wisconsin Press. 212 p. Alpizar, L.A., H.W. Fassbender and J. Heuveldop. 1983. Estudio de sistemas agroforestales en el Experiment0 Central del CATIE, Turrialba. 111. Producci6n de residuos vegetales. CATIE, Turrialba, Costa Rica. 13 p. (mimeo). Alpizar, L., H.W. Fassbender, J. Heuveldop, H. Folster and G. Enriquez. 1986. Modelling agroforestry systems cacao (Theobroma cacao), with laurel (Cordia alliodora), and poro (Eythrina poeppigiana) in Costa Rica. I. Inventory of organic matter and nutrients. Agroforestry Systems 4(3):175-190. Benavides, J.E. 1983. Investigacidn en arbales forrajeros. In Curso Corto Intensivo sobre Tbcnicas Agroforestales Tradicionales. CATIE, Turrialba, Costa Rica, 8-18 Nov., 1983. 27 p. Benavides, J.E. 1985. Produccidn y calidad nutritiva del forraje de pasto kinggrass (Penniseturn putpureurn x P. typhoides) y por6 (Erythrina poeppigiana) sembrados en asociaci6n. CATIE, Turrialba, Costa Rica. 37 p. (mimeo). Borchert, R. 1980. Phenology and ecophysiology of tropical trees: Etythrina poeppigiana O.F. Cook. Ecology 61(5):1065-1074. Bronstein, G.E. 1984. Producci6n comparadade una pastura de Cynodon plectostachyus asociada con Arboles de Cordia alliodora, asociada con Irboles de Erythn'na poeppigiana y sin &boles. M.Sc. Thesis UCR-CATIE, Turrialba, Costa Rica. 109 p. Budowski, G . , R.O. Russo and E. Mora. 1985. Productividad de una cerca viva de Erythrina betiemana Urban en Turrialba, Costa Rica. Turrialba 35(1):8386. Cadima Zeballos, A. and P. de T. Alvim. 1967. Influencia del Brbol de sombra Erythrina glauca sobre algunos factores edafoldgicos relacionados con la producci6n del cacaotero. Turrialba 17(3):330-336. Centro Agronbmico Tropical de Investigaci6n y Ensefianza. 1986a Bibliography on the genus Eythrina. CATIE, Renewable Natural Resources Department, Turrialba, Costa Rica. 182 p. Centro AgronBmico Tropical de Investigacidn y Ensefianza. 1986b. Final project technical report: Erythrina spp. (phae 1 : 3-p-82-0015). CATIE, Turrialba, Costa Rica. 182 p. Cook, O.F. 1901. Shade in coffee culture. U.S. Department of Agriculture, Division of Botany, Washington, D.C. 79 p.

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Cook, O.F. and G.N. Collins. 1903. Economic plants of Porto Rico. In Contributions from the US. National Herbarium 8(2):57-269. Duke, J.A. 1972. Isthmian etnobotanical dictionary. Fulton, Maryland, J.A. Duke. 96 p. Dwyer, J. and W.G. D'Arcy. 1980. Eythrina. In Flora of Panama. Part V. Annals of the Missouri Botanical Garden 67(3):686-697. Enriquez, G. 1983. Breve reslimen de 10s resultados del Experiment0 Central de plantas perennes de La Montafia, CATIE, Turrialba, Costa Rica. Agroforestry Short Course 1983. CATIE, Turrialba, Costa Rica. 13 p. (mimeo). Escalante, G., R. Herrera and J. Aranguren. 1984. Fijaci6n de nitr6geno en hrboles de sombra (Erythrina poeppigiana) en cacaotales del norte de Venezuela. Pesquisa Agropecuaria Brasileira 19(suppl.):223-230. Fassbender, H.W., L. Alpizar, J. Heuveldop, H. Folster and G. Enriquez. 1986. Modelling agroforestry systems cacao (Theobroma cacao), with laurel (Cordia alliodora), and poro (Etythrina poeppigiana) in Costa Rica. 111. Cycles of organic matter and nutrients. Agroforestry Systems 6(1):49-62. Feinsinger, P., Y.B. Linhart, L A . Swarm and J.A. Wolfe. 1979. Aspects of the pollination biology of three Etythrina species on Trinidad and Tobago. Annals of the Missouri Botanical Graden 66(3):451-471. Folkers, K. and K. Unna. 1939. Etythrina alkaloids. V. Comparative curare-like potencies of species of the genus Eryfhrina. J. Am. Pharm. Assoc. 28:10191028. Flye, W.D. 1945. Erylhrina umbrosa e a sombra "inbmortal" para e cafeiro. Boletin Superintendencia dos Servicios do Cafe (Brazil) 20:878-879. Glover, N. and J. Beer. 1984. Spatial and temporal fluctuations of litterfall in agroforestry associations Coffea ambica var. Caturra-Eythrina poeppigiana and C. arabica var. Caturra-E. poeppigiano-Cordia alliodora. CATIE, Turrialba, Costa Rica. 43 p. (mimeograph). Glover, N. and J. Beer. 1986. Nutrient cycling in two traditional Central American agroforestry systems. Agroforestry Systems 4(2):77-88. Hardy, F. 1961. Manual de cacao. Turrialba, Costa Rica, IICA. p. 28. Heuveldop, I., H.W. Fassbender, L. Alpizar, G. Enriquez and H. Folster. 1986. Modelling agroforestry systems cacao (Theobroma cacao), with laurel (Cordia alliodora), and poro (Elythrina poeppigiana) in Costa Rica. 11. Cacao and wood production, litter and decomposition. Agroforestry Systems 6(1):37-48. Holdridge, L.R. 1955. La agricultura y la dasonomia en Costa Rica: Competencia o coexistencia. Comunicaciones en Turrialba no. 56. Setiembre 1955. Holdridge, L.R. 1967. Arboles de sombra para el cacao. In Manual del Curso de Cacao. IICA, Turrialba, Costa Rica. pp. 113-117. Holdridge, L.R. and L. Poveda, 1975. Arboles de Costa Rica. v.1. San Jost, Costa Rica, Centro Cientifico Tropical. 546 p. Kass, D.C.L., R.O. Russo and M.M. Quinlan, 1983. Leguminous trees as nitrogen source for annual crops. Agronomy Abstracts 1983. p. 45. Kass, D.C.L. and A. Banantes. 1984. Leguminous trees as nitrogen source for annual crops. CATIE, Turrialba, Costa Rica. 31 p. (mimeo).

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