Enterolobium cyclocarpum: the ear pod tree for fasture, fodder and wood
Enterolobium cycloca, pum (Jacq.) Griseb. is one of the largest
trees in the dry forest formation of Mexico and Central America, reaching up to
3 m diameter and 40 m in height with a huge spreading crown. It is a conspicuous
and well-known tree in its native range. Large crowned trees scattered in
pastures are a common sight and a distinctive feature of the landscape in many
parts of Central America. Such is its fame that Enterolobium has been adopted as
the national tree of Costa Rica. The province of Guanacaste in Costa Rica is
named after Enterolobium which occurs abundantly in that area.
Enterolobiant cyclocarpum is also well-known for its
distinctive, thickened, contorted, indehiscent pods which resemble an ear in
form. Most of the common names for Enterolobium refer to this resemblance,
including ear fruit, ear pod, orejon (from Spanish oreja an ear) and guanacaste
(conacaste, a NahuatI derivation signifying ear tree).
BOTANY:
The nitrogen ftxing tree Enterolobium cvclocarpum belongs to the
subfamily Mimosoideae of the Leguminosae and is placed in the tribe lngeae. The
genus Enterolobium is closely related to Albizia and Samanea and is probably
only maintained as a separate genus due to its widespread cultivation.
Enterolobium contains only five species, all from Central and South America, and
only E. cyclocarpum is widely cullivated. Closely related species, such as E.
schomburgkii Benth., remain untested to date.
Enterolobium leaves are bipinnately compound with opposite
leaflets. Small white flowers occur in compact round heads. In Central America
E. cyclocarpum is sometimes confused with Albizia niopoides (Guanacaste blanco)
due to similarity in tree form but may be readily distinguished by the different
bark which is pale golden yellow in A. niopoides.
ECOLOGY:
Enterolobium cyclocarpum occurs from latitude 23°N in
central Mexico, south through Central America, to TN in northern South America.
It has been widely introduced throughout the tropics where it is cultivated
mainly as a roadside or garden tree. In its native range, Enterolobium occurs in
a wide range of different forest types from tropical, dry deciduous forest to
tropical moist forest. It becomes a climax tree only in the dry forest, being
restricted to disturbed areas in wetter forest types. Enterolobium cyclocarpum
is a lowland species occurring from sea level to 1200 m elevation and has only
very limited tolerance of frost.
Enterolobium cyclocarpum
Annual rainfall varies between 750-2500 mm through most of its
native range with a dry season that lasts 1-7 months. Trees are generally
deciduous, losing their leaves during the dry season and flushing out again
about two months before the onset of the rainy season. Flowering starts while
the trees are leafless (March-April in Central America), and the pods take a
year to mature, ripening in April-May.
USES:
The wide spreading canopy of a mature Enterolobium makes it an
ideal shade tree, whether for livestock in pasture lands, for perennial crops
such as coffee, or in roadside and urban plantings. Its value to livestock is
further enhanced by production of large quantities of highly palatable and
nutritious pods containing a sugary dry pulp. Pods are generally shed at the end
of the dry season in Central America when livestock feed is particularly short.
Pods fall from the trees gradually over a period of two months thus spreading
the availability of pods for livestock. Data from Puerto Rico suggests that pod
production may be delayed as much as 25 years after planting. The foliage is
also palatable, though to a lesser extent than the pods, which results in high
mortality of natural regeneration in pasture lands and may explain why the tree
occurs naturally only as scattered individuals.
Enterolobium heartwood is reddish-brown, coarse-textured and
moderately durable, with a straight interlocking grain and an appearance
somewhat similar to walnut. Specific gravity is variable, ranging from 0.40.6.
The wood is resistant to attack by dry-wood termites and Lyctus, and can be used
in house construction as well as for nonstructural interior elements including
panelling. The white sapwood, by contrast, is highly susceptible to insect
attack. Enterolobium wood may also be used for boat-building because of its
durability in water; it has been used in the past for water-troughs and dug-out
canoes. The dust from sawmilling can produce allergic reactions in workers.
Other uses include food (the immature pods as a cooked
vegetable, or the seeds toasted and ground), soapmaking (using tannins from the
pods and bark), and medicinal use of bark extracts against colds and bronchitis.
The ability of Enterolobium to fix nitrogen, and to resprout vigorously when
coppiced, suggest it could also have a role in alley-cropping systems as a
hedgerow species, though this is an area requiring further research.
SILVICULTURE:
Enterolobium is a light-demanding species at all stages in its
development. It is susceptible to weed competition during early, growth.
Enterolobium resprouts vigorously after coppicing or lopping; indeed, it is
difficult to kill Enterolobium by girdling because of its tendency to resprout
below the girdle line. Little information is available, however, on its response
to repeated cutting. With no silvicultural intervention it usually occurs as a
single, large, open-grown tree, though pruning can improve the length and form
of the bole.
Enterolobium can tolerate a wide range of soil types, from
alkaline and calcareous to somewhat acidic (pH as low as 5), provided that
aluminum saturation is not a problem. Best growth is on deep, medium-textured
soils but sandy and clay soils also allow good development provided drainage is
unimpeded. The trees will not thrive on sites prone to waterlogging.
PROPAGATION:
The combination of large nutritious pods and seeds with hard
coats is ideal for seed dispersal of Enterolobium by animals. Seeds are most
easily collected by waiting for pods to fall. An adult tree produces an average
of 2000 pods, each with 10-16 seeds (9001200/kg). Trees produce seed crops in
most years in Central America. Seed extraction from the indehiscent pods is
usually carried out by manual threshing, milling or maceration of the pods
followed by winnowing and screening.
Enterolobium seed is naturally scarified by passage through the
gut of large herbivores. It is likely that the original consumers of
Enterolobium pods are now extinct and their role as seed dispersal agents has
been assumed by horses and cattle. Collected seed requires pretreatment before
sowing to allow water to penetrate the seed coat. Manual scarification is
effective, as is treatment with hot water or concentrated sulfuric acid. A
suitable hot water treatment is a brief (30 second) soak in water close to
boiling point, followed by 24 hours in water at room temperature. Enterolobium
seeds remain viable for several years under cool, dry conditions and can be
easily stored under normal conditions.
Seed supplies are currently dependent on collections from
natural populations in Latin America and scattered cultivated trees in areas
where Enterolobium has been introduced. Most early introductions of E.
cyclocarpum were undocumented, casual and collected from a narrow genetic base.
A broader range of representative germplasm should be tested to evaluate the
potential of the species. Seed is available from OFI and NFTA for the
establishment of field trials.
The seed should be sown 1-2 cm deep with the micropyle pointing
downwards; the emerging root is not strongly geotropic and may come up out of
the soil if the seed is planted upside down. Early seedling growth is rapid and
vigorous. This early advantage over smaller-seeded species can continue several
months after outplanting, but thereafter growth rate, though still vigorous, is
no longer exceptional relative to other fast growing species.
PESTS AND DISEASES:
Enterolobium has no serious or widespread disease and insect
problems, although attack by a Fusarium fungus, with associated damage by
wood-boring insects, can cause affected limbs to fall from mature trees.
Branches may also be broken off by storm damage. Both factors reduce the
desirability of Enterolobium for urban and roadside planting. Although no
bruchid seed predators are found on E. cyclocarpum, the green pods are often
preyed upon by parrots and fruiting may be further disrupted by the gall forming
moth Asphondylia enterolobii.
PRINCIPAL REFERENCES:
Echenique-Manrique, R. and R.A. Plumptre. 199.0. A guide to the
use of Mexican and Belizean timbers. Tropical Forestry Paper 20. Oxford Forestry
Institute, UK. 175 p.
Francis, J.K. 1988. Enterolobium cyclocarpum (Jacq.) Griseb.
Guanacaste, Earpod-tree. Leguminosae. Legume Family. USDA Forest Service.
Southern Forest Experiment Starion. SO-ITF-SM-15.
Janzen, D.H. 1983. Enterolobium cyclocarpurn. In D.H. Janzen
(ed), Costa Rican Natural History. Univ. Chicago Press. Chicago, IL. 816 p.
Little, E.L., R.O. Woodbury, and F.H. Wadsworth. 1974. Trees of
Puerto Rico and the Virgin Islands, Vol. 2. USDA Agric. Handbook No. 449. p.
258-259.
Standley, P.C. and J.A. Steyermark. 1946. Enterolobium.. In
Flora of Guatemala. Fieldiana: Botany 24(V):32-34.
NFTA 94-02 January
1994
