Cecropia peltata L.
Yagrumo Hembra, Trumpet-Tree
Moraceae -- Mulberry family
Susan R. Silander and Ariel E. Lugo
Yagrumo hembra (Cecropia peltata), also called trumpet-tree, is a rapidly growing neotropical tree, an important secondary species that is common in Puerto Rico. It is an early invader of forested areas subject to natural or human disturbances and is conspicuous due to its spreading crown and large peltate leaves 30 to 50 cm (12 to 20 in) in diameter, with silver-white lower surfaces.
Yagrumo hembra is also native throughout the Greater and Lesser Antilles and in Central America from Yucatan, Mexico, to Costa Rica. In South America it has been reported from Venezuela, Colombia, Brazil, and the Guianas (19).
In Puerto Rico, yagrumo hembra is found most frequently in the wetter life zones: Subtropical Moist Forest, with 990 to 2010 mm (39 to 79 in) of precipitation annually; Subtropical Wet Forest, with 2010 to 3990 mm (79 to 157 in); Subtropical Rain Forest, with 3810 mm (150 in) and greater; Subtropical Lower Montane Rain Forest, with 2010 to 3990 mm (79 to 157 in); and Subtropical Lower Montane Wet Forest, with 3810 mm (150 in) and greater. Mean annual temperatures in the lower montane life zones range from 12° to 18° C (54° to 64° F), whereas in the lower elevation life zones the range is from 18° to 24° C (64° to 75° F). The species is rare or absent in the Subtropical Dry Forest life zone.
Yagrumo hembra grows on the Ultisols of the central and eastern mountains of Puerto Rico, the Mollisols and Alfisols of the limestone hills of the northwest, the Oxisols of the western mountains underlain by serpentine, and also the Mollisols and Inceptisols of the northern coastal plain. It is found from 50 to 1300 in (164 to 4,265 ft) in elevation on ridges, slopes, and flats but appears to be at its optimum in coves or protected areas. It is often found on steep slopes where landslides or tree falls have occurred, and in these areas its prop or stilt roots may be conspicuous. Yagrumo hembra grows on alluvial, colluvial, and residual soils neutral to acidic in nature. These soils may be derived from tuffs; volcanic rock, andesitic or dioritic in composition; limestone; or serpentine. Soil texture may range from heavy clay to sandy, but a clay-loam soil is optimal.
As a secondary species, yagrumo hembra frequently invades forest gaps or openings, roadsides, streamsides, and landslides in moist, wet, and rain forest life zones of Puerto Rico. In the Luquillo Mountains in eastern Puerto Rico and in the central mountains it is widely distributed in the Lower Montane Forest, Montane Rain Forest, and Elfin Woodland formations of these life zones (1). In the Elfin Woodland it is short in stature and gnarled, as are its associated species in this formation.
Yagrumo hembra is frequently associated with other secondary species such as yagrumo macho (Didymopanax morototoni) and guano (Ochroma pyramidale). The scattered presence of this secondary species among species more characteristic of a mature stand indicates that a disturbance, such as tree fall, storm damage, or landslide, occurred at some time in the past. Although initially dependent upon the size of the openings, pure dense stands of yagrumo hembra, once established, may persist for several years following the disturbance. The species may also be found, in a dominant or codominant canopy position, associated with primary species such as tabonuco (Dacryodes excelsa), motillo (Sloanea berteriana), and ausubo (Manilkara bidentata) in the Lower Montane Rain Forest; palo colorado (Cyrilla racemiflora), caimitillo (Micropholis chrysophylloides), and camasey jusillo (Calycogonium squamulosum) in the Montane Rain Forest; and roble de sierra (Tabebuia rigida) and nemoca (Ocotea spathulata) in the Elfin Woodland.
Yagrumo hembra is less common in the hotter lowlands of Puerto Rico. Here it may be an infrequent component of succession primarily on the wetter sites following cultivation, associated with the secondary species listed above as well as with many introduced species. In the mogotes or limestone hills of northwestern Puerto Rico, yagrumo hembra is associated with those secondary species described previously as well as others such as ucar (Bucida buceras), almacigo (Bursera simaruba), and espino rubial (Zanthoxylum martinicense).
Flowering and Fruiting- Yagrumo hembra is dioecious, with staminate flowers borne in slender, stalked aments 5 to 6 cm (2.0 to 2.4 in) in length, arranged in clusters of as many as 15, and pistillate flowers in thicker, stalkless aments grouped in clusters of only 2 to 5. Both staminate and pistillate trees may be observed in flower and fruit all year long; however, a peak flowering and fruiting period occurs in Puerto Rico during the months of January to March, the drier season. This is also the period of minimum temperatures and minimum day-length (8,26). A winter flowering and fruiting peak for yagrumo hembra has also been noted in San Pedro de Montes de Oca (1200 m or 3,937 ft) in Costa Rica (9).
The slightly fleshy multiple fruit is at maturity gray-green in color and may be 10 cm (4 in) in length and 15 mm (0.6 in) in diameter. It is composed of numerous individual fruits, pentangular or hexangular in shape, each of which contains one brown seed of about 2 mm (0.08 in) in length. There are 2,500 seeds per gram (70,875/oz), air dried. The extraction factor for seeds is about 20 percent, because of the gummy material surrounding each seed (16). Maturation, from emergence of the inflorescence from the terminal bud to full ripening, requires from 3.5 to 4 months. Staminate inflorescences remain on the tree for only 1.5 months and produce copious amounts of wind-borne pollen approximately 1 to 1.5 months following emergence from the terminal bud (26).
Seed Production and Dissemination- Although as many as 15,000 flowers may be produced per inflorescence, the number of seeds that mature fully may be as low as 18 percent, or 2,725 viable seeds per inflorescence. Seed production by a mature tree during one reproductive year has been estimated to be as high as I million (13,26). Seed production is size or age specific, however, and increases throughout the lifetime of the tree. In an estimated life span of 30 years, as many as 6 to 7 million seeds may be produced by a single tree. Reproductive maturity is reached at an earlier age, 3 or 4 years by pistillate than by staminate trees, which mature at 4 to 5 years. Reproductive age may depend upon need for allocation of resources to rapid initial height growth and therefore the height and proximity to surrounding vegetation. Roadside trees, in a more open environment, reached reproductive maturity sooner (3 to 4 years) than forest gap trees (5 to 6 years) (26). Seed production probably decreases as a tree approaches the senescent state. In this stage there appears to be an increase in branch loss.
Seeds are dispersed primarily by bats and birds (3,7,11,18,24); seeds pass through the digestive tracts unharmed (24). In Puerto Rico, 15 species of birds and bats have been reported to feed on mature yagrumo hembra fruit. Some of the more common species include the Jamaican fruit eating bat, the banana quit, the pearly-eyed thrasher, the red-legged thrush, and the reina mora (18,26).
These species frequent both open and forested areas, so that seeds are dispersed widely and are available in forest soil in the event of a disturbance (12). As many as 398 seeds per square meter (37/ft²) have been reported to be present in undisturbed lower montane rain forest soil (2,26). Blum (3) reported that yagrumo hembra seedlings grew in 4 to 10 soil samples taken from mature forests in Panama. Other secondary species such as yagrumo macho, cachimbo comun (Psychotria berteriana), and guano were also present in these soils.
Seeds may also be dispersed when the entire fruit cluster falls to the ground upon ripening, but these seeds show a reduced viability as the embryos are damaged by fungi and insects of the family Nitidulidae. Laboratory- stored seeds retained viability for a minimum of 6 months, whereas seeds stored on the forest floor retained viability for only 2 to 3 months. This reduced viability under natural conditions indicates that a constant addition of seeds to the seed bank of the forest floor is necessary for rapid and successful colonization of a forest gap.
Seedling Development- Seeds require full sunlight for successful germination. Thus, seeds present on the floor of closed forests germinate only when some type of canopy gap occurs. Given full light conditions, germination may be as high as 80 to 90 percent (3,16,26). Germination is epigeal and in an open field was shown to be reduced by the presence of a layer of leaf litter. Other factors that may interact with increased light intensity in promoting germination include higher surface soil temperatures, fluctuations in air temperature, and changes in soil moisture. With the decreased light intensity beneath the closed forest canopy, spectral composition (an increased proportion of infrared light) may also become critical to germination (26). A decreased ratio of infrared to red light has been shown to inhibit germination of successional species. In open fields there was less yagrumo hembra seed germination than was observed in light gaps. This may result from the extremely high and fluctuating surface soil temperatures or to fluctuating but frequently low soil moisture, or both (table 1).
|Relative humidity, %|
|Soil moisture, % dry wt.||47.8||78.3||47.6|
¹Values are means for all months, August 1977 to January 1878 (25).
In the nursery, seed is germinated under light shade on a seedbed prepared from equal parts of clay, sand, and filter press cake. Light shade is maintained until seedlings shade the germination media (16).
Seedling leaves are distinct from those of the mature plant. They are downy on both surfaces, lanceolate, unlobed, and finely toothed. In the early sapling stage, 0.5 m (1.6 ft) tall, leaves begin to show signs of lobing. Ultimately, new leaves have 7 to 11 palmate lobes and resemble those of the mature plant, dark green and scabrous above and covered with a dense surface of white hairs below. Seedlings grow rapidly in height, reaching 10.0 to 15.0 cm (3.9 to 5.9 in) in 10 weeks (16) and as much as 2.1 m (6.9 ft) in the first year (21). The ratio of photosynthesis to respiration of yagrumo hembra seedlings has been reported to be much greater than 1 (20).
Under natural conditions, seedling mortality may be extremely high. In a forest opening, 99 percent of germinating seedlings may die within the first year. This is the life stage during which the greatest mortality occurs. During nursery trials, volunteer seedlings suffered 45 percent mortality during the first 9 months (10). However, seedlings transferred when 25.0 to 60.0 cm (9.8 to 23.6 in) in height to the field following a 2-week shaded period and gradual diminishing of shade showed a survival of as high as 80 percent. In 7 months they had reached 2.0 m (6.6 ft) in height (16).
-Survivorship curve for yagrumo hembra. A is based on
disturbed areas; B is based on life cycle stages (26).
Growth in height is most rapid during the first 4 to 5 years, but the tree grows relatively little in diameter during the same period (6). In the Luquillo Mountains of eastern Puerto Rico, maximum seedling height growth under natural conditions was 1.14 in (3.7 ft) and the mean 0.73 m (2.4 ft) per year. Maximum diameter growth measured immediately above the root collar was 5 mm (0.20 in) and the mean growth was 3.6 mm (0. 14 in) during an 8 month period (26).
Seedlings which are overtopped and thus shaded for extended periods of time do not survive for long. Potted seedlings transferred from a forest gap to closed forest died within several months and showed little if any growth. Potted seedlings remaining in the gap exhibited 100 percent survival as well as diameter and height increases. A disturbed area that is invaded rapidly by grasses, ferns, or vines shows a decreased density of yagrumo hembra during the seedling and sapling stages (26).
Vegetative Reproduction- Yagrumo hembra sprouts easily.
Growth and Yield- The sapling life stage begins when lobing of new leaves increases. Diameter growth of nonsuppressed saplings is significantly faster than that of seedlings. At an elevation of 400 m (1,312 ft) in the eastern mountains of Puerto Rico, saplings grow a maximum of 3.0 cm (1.2 in) and a mean of 6.5 mm. (0.26 in) in diameter per year. Mean growth in d.b.h., as opposed to maximum d.b.h. growth, is low due to the presence of numerous suppressed saplings in the dense stands which often occur following disturbance. These saplings grow as much as 2.16 m (7.1 ft) in height per year (26).
A method has been developed for determining the age of yagrumo hembra based on past height growth (6). The tree has conspicuous rings and large triangular leaf scars at each node. Turrialba, where the study was conducted, has a distinct dry season, and internodes are arranged in short and long series. Short internodes represent growth during the drier season and long internodes growth during the wetter season. Annual height growth was found to be faster in wetter (5.9 m or 19.3 ft and 7.6 m or 24.9 ft) than in drier (1.9 in or 6.2 ft and 2.4 m or 7.9 ft) regions. It should be stressed that this method is only reliable for trees less than 5 years in age as height growth slows significantly later in life (6). Another method for aging yagrumo hembra is based on regressions of height and diameter on age. Since this method was developed for young trees and uses mean d.b.h. and mean height of a stand, it may more accurately estimate stand than individual age (26).
-Estimation of age of yagrumo hembra from diameter adn height.
A = regression of age of disturbed area on mean height (solid dot). Y = 0.91 + 1.3X, r² = 0.8. B = regression of age of disturbed area on mean d.b.h. (open dot). Y = 0.90 + 0.86X, r² = 0.9 (26).
Periodic diameter growth of 4.6 to 5.1 mm. (0.18 and 0.20 in) was measured for yagrumo hembra (5). Growth rates were among the slowest measured in the Luquillo Mountains. A mean annual growth rate in d.b.h. of 2.0 mm (0.08 in) has been reported for mature yagrumo hembra trees (23) and an annual diameter growth rate of 6.4 mm (0.25 in) was measured in mature dominant trees (26). Once yagrumo hembra trees reach maturity, diameter growth appears to decrease. Growth is greatly improved by a dominant crown position, but little difference is found among codominant, intermediate, and suppressed trees. Trees in plantations reach a diameter of 25.0 cm (9.8 in) and a height of 14.0 m (45.9 ft) in 21 years (25). Height growth in yagrumo hembra predominates over diameter growth (23). This pattern fits well the ecological role of yagrumo hembra as a gap species.
In the Luquillo Mountains, the density of yagrumo hembra in the tabonuco forest association (Subtropical Wet) is 83 trees per hectare (34/acre), and at a higher elevation in the Colorado forest association (Lower Montane Wet) it is 17 trees/ha (7 trees/acre) (28). Yagrumo hembra had a mean basal area of 18.3 to 22.9 m² /ha (79.7 to 99.7 ft²/acre) in the tabonuco forest (16). In a 2-ha (4.9-acre) sample of tabonuco forest, approximately 25 percent of the trees were 10 to 15 cm (3.9 to 5.9 in) in d.b.h, 26 percent were 15 to 20 cm (5.9 to 7.9 in), 20 percent were 20 to 25 cm (7.9 to 9.8 in), and 13 percent were 25 to 30 cm (9.8 to 11.8 in). Only 6 percent had diameters of greater than 50 cm (19.7 in).
Trees reach canopy height at about 10 years of age and thereafter survive in the canopy for approximately 20 years. Mean further life expectancy, 10.25 years, is greatest as the tree approaches the canopy. High mortality occurs between the production of seed and the establishment of seedlings (fig. 2).
Rooting Habit- The root system of yagrumo hembra tends to be superficial, and therefore the tree is easily uprooted, particularly when immature. Prop or stilt roots are a prominent feature and are often as much as 1.0 m (3.3 ft) in height.
Reaction to Competition- Yagrumo hembra is most accurately classed as intolerant of shade. This is especially true during the seedling and sapling stages. Competition for light and space during these stages may be the principal factor influencing growth and survival.
Damaging Agents- In the seedling and sapling stages a major cause of mortality is defoliation by the larvae of the following: Prepodes spp., Gynaecia dirce, Historis odious, Correbidia terminalis, and Sylepta salicalis (22). The cotton or melon aphid (Aphis gossypii) is also commonly observed on leaves of yagrumo hembra.
The above species often cause heavy damage to the leaves of mature trees. Strangulation by vines, including those of the families Leguminosae, Convolvulaceae, and Malpighiaceae (27), as well as many species of Philodendron, is also a major cause of mortality, particularly during the sapling stage. Mortality of mature trees may be caused by storm damage to the easily broken branches, by advancing age, or by environmental changes, such as shading and root competition, caused by the reestablishment of the climax forest.
As a dominant secondary species, yagrumo hembra is invaluable in regeneration of the forest following disturbance. As it rapidly forms a dense stand, nutrients may be conserved and the environment beneath ameliorated sufficiently to allow species characteristic of a later stage of succession to germinate and grow. In this manner the soil may be stabilized following a disturbance such as a landslide. Its broad canopy protects the soil from excessive erosion and reestablishes shade conditions to the forest floor.
With a specific gravity of 0.29, the wood of yagrumo hembra is only slightly heavier than local balsa. The wood is used in the finish of "puertorrican cuatros," a local guitarlike musical instrument. Principal uses for wood in Puerto Rico once included excelsior. The wood also was shredded and mixed with cement to form a building or insulation board (4). Elsewhere, yagrumo hembra is used to produce paper pulp. Fiber yield per cord of fresh material is low, but it cooks rapidly, giving unbleached pulps that approach the best northern deciduous neutral sulfite pulps, e.g., aspen, in quality. A yield of 56 kg (123.5 lb) of pulp per 100 kg (220.5 lb) of wood has been estimated (17). The wood may be substituted for use in products made from heavier grades of balsa. It is also used for boxes, crates, and matchsticks (19). The hollow branches are often split and used for gutters or troughs, and entire branches are used for pipe floats, life preservers, and tamborines.
Various substances have been extracted from yagrumo hembra for medicinal use (19), including one that increases cardiac muscular contraction and acts upon the kidneys as a diuretic. A substance extracted from the roots is said to heal wounds, and the leaves are often used as a poultice to reduce swelling and as an abrasive (27).
Vegetative morphology of yagrumo hembra throughout the islands of the Caribbean differs from that of mainland (Central and South America) representatives of the same species. On the mainland, yagrumo hembra maintains a symbiotic relationship with Azteca ants. The species Azteca constrictor and A. alfaroi have been reported from Venezuela (27). There the tree also has adaptations, such as a trichilium or highly modified petiole bases that produce mullerian bodies or food bodies rich in glycogen. The stinging, aggressive ants live in the hollow internodes and feed upon glycogen produced by the tree. Neither the adaptations nor the ants are present on trees in Puerto Rico. In the Caribbean islands from Trinidad to Puerto Rico there is a progressive loss of these ant-related traits (25). Mainland individuals maintain trichilia in the greenhouse; these appear to be genetic traits and do not depend on ant stimulation for development (14,25).
Approximately 80 species of the genus Cecropia have been described; however, only one species is found on the islands of the Caribbean. A chromosome number of 2n=28 has been reported (27). Velazquez (27) consolidated three Venezuelan Cecropia species into a variety of C. peltata: Cecropia peltata L. var. candida.
Recently, Howard (14) describes Puerto Rican species as Cecropia schreberiana rather than C. peltata, stating that the latter is restricted to mainland Central and South America and Jamaica. C. schreberiana is mentioned as occurring throughout the remainder of the Greater and Lesser Antilles. Some place it in its own family, cecropiaceae, with the genus Cecropia as the type genus.