Manilkara bidentata (A. DC.) Chev.
Sapotaceae -- Sapodilla family
P. L. Weaver
Ausubo (Manilkara bidentata), also known a balata, is a large evergreen forest tree that was probably the most important timber tree of Puerto Rico. It grows best in Puerto Rico on alluvial plain where it may reach the age of 400 years. Ausubo is extremely tolerant of shade. The strong and attractive wood makes it highly valued commercially an it is widely used in the tropics for many woo products. The tree is often tapped for its milky latex the source of balata gum. Although growth is slow, ausubo is planted for shade and timber.
Ausubo is native to Puerto Rico, widely distribute throughout the West Indies, and ranges from Mexico through Panama to northern South America, including the Guianas and Venezuela, to Peru, and to northern Brazil (9,22).
In Puerto Rico, ausubo is native to the moist coastal and limestone forests, and to lower mountain forests. Ausubo ranges from near sea level up to 60 in (2,000 ft) in elevation. The tree is a primary species and is very shade tolerant.
In Puerto Rico, ausubo is found in the Subtropical Moist, Subtropical Wet, and Subtropical Rain Forest life zones. Annual rainfall in these forests varies from 1500 to 4000 mm (59 to 157 in). Temperatures range from a mean minimum in January of 16° C (61° F) to a mean maximum of 31° C (88° F) in August (8), the extremes for the range of ausubo or the island. Evapotranspiration over the same regions varies between 1400 and 1800 mm/yr (55 and 71 in/yr), with the lowest measurements in the mountainous interior.
Throughout the West Indies, ausubo grows in areas where the annual rainfall varies from 1500 to 4000 mm (59 to 157 in) (table 1). In South America many areas probably receive more than that amount In the Bajo Calima region of Colombia, west of the city of Cali, annual rainfall in Tropical Rain Forest approaches 7000 min (276 in). All sites are frost free.
|Country||Forest type classification¹||Annual rainfall|
|Puerto Rico (16)||Subtropical Moist Forest¹||1000 to 2000||39 to 79|
|Subtropical Wet Forest¹||2000 to 4000||79 to 157|
|Dominica (16)||Lower Montane Rain Fore St²||-3000||-118|
|Secondary Rain ForeStS²||-2000||-79|
|St. Lucia (4)||Lowland Rain ForeStS²||2000 to 2500||79 to 98|
|Lower Montane Rain ForeSt²||-3000||-118|
|Secondary WoodlandS²||2000 to 2500||79 to 98|
|Grenada (4)||Lowland Rain ForeSt²||2000 to 2500||79 to 98|
|Lower Montane Rain ForeSt²||-3000||-118|
|Dry Scrub Woodland²||-1500||-59|
|Secondary Rain Forest²||2000 to 2500||79 to 98|
|Barbados (4)||Dry Scrub Woodland²||-1500||-59|
|British Virgin Islands (4)||Xerophytic Rain ForeSt²||-1500||-69|
|Trinidad (3)||Lower Montane Rain ForeSt²||2000 to 2500||79 to 98|
|Colombia (19,32)||Tropical Rain Forest¹||-7000||-276|
|Tropical Moist Forest¹||2000 to 4000||79 to 157|
|British Guyana (17)||Evergreen Seasonal ForeSt²||1700 to 1900||67 to 75|
|Venezuela (3)||Lower Montane Rain Forest¹||2000 to 3000||79 to 118|
|Suriname (20,31)||Rain Forest³||2000 to 2500||79 to 98|
|Upland Rain Forest³||2000 to 2500||79 to 98|
¹Holdridge (18)-Puerto Rico.
²Beard (1,2,3,4,5)-Dominica, St. Lucia, Grenada, Barbados, British Virgin Islands, Trinidad, Columbia, Guyana, and Venezuala.
In Puerto Rico, ausubo is native to acid, clay soils derived in situ, or deposited by alluvial or colluvia processes. Existing inventories indicate that it grow mainly on soils of the orders Inceptisol and Oxisol Parent rocks include andesites and limestone. In Trinidad, ausubo thrives on a variety of soils ranging from clays through sands, including rocky soils, and on several different geologic formations (27). Physiographically, it is found on slopes and flats, and in coves. In Trinidad it is common on hills, and in Puerto Rico, it attains its best development on alluvia plains. In Suriname, it is common along river banks (31)
In Puerto Rico, ausubo is associated with tabonuco (Dacryodes excelsa), guaraguao (Guarea guidonia) granadillo (Buchenavia capitata), and motillo (Sloanea berteriana) in the Subtropical Wet Forest classification according to Holdridge (18). In the Luquillo Mountains of northeastern Puerto Rico, species assemblages produced by the use of statistical clustering techniques revealed that ausubo occurs on upper slopes along with granadillo (13).
Elsewhere within its range, ausubo is a constituent of several different forest types (table 1), attaining its best development in Lowland Rain Forest, or Lower Montane Rain Forest (classification according to Beard) (1,2,4,5).
Species associated are numerous and vary with locale (4). In Trinidad, for example, ausubo is found in the Dry Evergreen Formation and Littoral Woodland along with royal palm (Roystonea oleracea), sierra palm (Prestoea montana), and timite (Manicaria saccifera). It is also found in Evergreen Seasonal Forest in the Carapa-Eschweilera association and in the Peltogyne association. Finally, it is found scattered in the Lower Montane Rain Forest.
Mature ausubo is characterized by a dense growth of horizontal branches with layered foliage and dark green elliptic alternate leaves with many faint parallel veins. A white latex appears in droplets from cut leaves and incisions in the trunk and stems. Large trunks have broad rounded buttresses spreading at the base.
In Puerto Rico, the tree attains a height of 30 m (100 ft) and diameter of 1.3 m (4 ft) on the best sites. On favorable sites elsewhere within its range, the tree will grow 45 m (150 ft) in height and nearly 200 cm (79 in) in diameter.
Flowering and Fruiting- In Puerto Rico, the white perfect flowers are borne annually on a stalk at the beginning of the wet season, mainly from May through late August, with occasional late autumn flowering. Fruits develop through the autumn with the principal fruit drop in winter and early spring (15). In Trinidad, ausubo flowers at the beginning of the dry season, January to February, and the fruit ripens by April and May (27). In both regions, good flowering and fruiting is at intervals of 3 to 4 years.
At randomly placed collection stations comprised of 0.5 m² (5.4 ft²) screen baskets in the Subtropical Wet Forest of Puerto Rico, ausubo dropped some 70 fruits in 39 months. Of the species of trees observed, ausubo ranked 16th in number of fruits collected (15).
Seed Production and Dissemination- Ausubo fruits are globose berries about 2.5 cm (1 in) in diameter and usually contain a single, shiny, black seed, surrounded by a sweet, gummy pulp that is edible. Occasionally, two seeds per fruit are found (21,27).
In unpublished experimental work conducted at the Institute of Tropical Forestry, 1,280 air-dried seeds per kilogram (580/lb) were counted. Cutting tests showed that 35 percent of the seeds were hollow. Moisture accounted for about 30 percent of the weight of the seeds.
Seed dispersal is limited to the vicinity of the parent tree unless animals consume or carry the fruits. Agouti and other animals eat the fruit in Trinidad (27), while in Puerto Rico birds have been identified as dispersal agents.
Seedling Development- Germination is epigeous and irregular over a long period, with some seed germinating in the second year. Trials in Trinidad yielded only 10 percent germination, and efforts to improve it by soaking in water or slightly cracking the seed were a failure (27). In Puerto Rico, 100 seeds per treatment were stored at room temperature and at 4° C (40° F) in paper sacks and sealed jars for periods of 1, 2, 3, and 6 months. A control was sown immediately. Germination for the treated seeds was essentially nil while the control showed 60 percent success. It was concluded that storage by the means tested was unsatisfactory. Seedlings in the wild are capable of growing under heavy shade and in herbaceous cover. Average height at the end of the first year is 12 cm (5 in), and after 5 years about 4.5 m (15 ft).
Artificial regeneration is best attained by direct sowing of fruits or transplanting of potted seedlings Ausubo seeds should be sown in moist leaves because they are not capable of emerging from the soil (26). "Limited success" has been achieved with bare root plantings after I year in the nursery, but if seedling are left too long in the beds, the taproot proves to b a problem (27).
In experimental work at the Institute of Tropical Forestry, seeds were sown in nursery beds in the su and under shaded conditions. After 10 months, those in the sun were twice as tall as the shade specimens. Direct out-planting of potted seedling under heavy shade in the limestone forest on the north coast showed survival rates greater than 9 percent after 10 months. The seedlings, however were sensitive to drought. Most had wilted and yellowed after a prolonged period without rain.
Vegetative Reproduction- Except when quite young, ausubo does not coppice, nor does it produce root suckers (27).
Growth and Yield- Growth of ausubo is slow in the sapling stage, and slow to intermediate in the pole stage through maturity. Height is about 0.3 m (1 ft) at 1 year, and about 4.5 m (15 ft) in 5 years. Annual diameter increment in an early secondary stand in St. Just (table 2), where the stems ranged from 4 to 13 cm (1.6 to 5.1 in) in diameter, averaged 0.58 cm (0.23 in) over a 2-year period.
On an understocked 0.4 ha (1 acre) plantation in Trinidad, after 21 years volume mean annual increment (MAI) averaged only 2.37 m³/ha (33.86 ft³/acre). Diameter and height MAI for plantations in both Trinidad and Puerto Rico show that the former varies from 0.51 to 0.81 cm (0.20 to 0.32 in), and the latter from 0.2 to 1.1 m (0.66 to 3.6 ft), depending on site (table 2). Measurements of annual diameter increments for 17 years in previously thinned Subtropical Wet Forest of the Luquillo Mountains shows an average annual growth of 0.51 to 0.58 cm (0.20 to 0.23 in).
|Site characteristics||Stand||Annual increment|
|Toro Negro (24)||900||2500||deep, acid clay||NA²||5||1.1||6.4||NA||NA|
|Toro Negro (25)||900||2500||deep, acid clay||NA||9||0.2||5.1||NA||NA|
|Central Range (27)||100||2000||NA||370||21||0.8||8.1||0.4||2.37|
|El Verde (29)||450||3000||deep, acid clay||700||2.5||NA||3.2||NA||NA|
|Sabana (14)||180 to 360||2300||deep, acid clay||800||17||NA||5.1||NA||NA|
|Rio Grande (14)||420 to 600||3000||deep, acid clay||800||17||NA||5.8||NA||NA|
|St. Just (34)||60||1900||shallow, acid clay||2460||2||NA||5.8||0.04||NA|
|Toro Negro||2,950||100||deep, acid clay||NA||5||3.6||0.25||NA||NA|
|Toro Negro||2,950||100||deep, acid clay||NA||9||0.7||0.2||NA||NA|
|El Verde||1,480||120||deep, acid clay||283||2.5||NA||0.13||NA||NA|
|Sabana||590 to 1, 180||90||deep, acid clay||324||17||NA||0.2||NA||NA|
|Rio Grande||1,380 to 1,970||120||deep, acid clay||324||17||NA||0.23||NA||NA|
|St. Just||200||75||shallow, acid clay||996||2||NA||0.23||0.09||NA|
¹For natural stands, all species of trees greater than 4 cm (1.6 in) in d.b.h.
Rooting Habit- By 2 years of age, the selling has a taproot. When older, it has a strong, moderately deep root system making the species wind-firm (27).
In the study of a single ausubo tree in the Luquillo Experimental Forest, a root-to-shoot-to-leaf ratio of 24 to 68 to 8 was found. Fibrous roots constituted 28 percent of the total root biomass (10).
Reaction to Competition- Ausubo is classed as very tolerant of shade throughout most of its life. It regenerates and is capable of growing through sapling, pole, and immature stages in dense shade. Basal area and diameter growth, however, are more rapid in trees that are exposed to the sun (29). In Trinidad, it was ranked second among the more valuable timber species with regard to shade tolerance (27). Its slow growth in seedling stages exposes it to damage by grazing animals and results in low survival rate for the species. In Puerto Rico, ausubo has been transplanted under fairly dense shelterwood (24) with good survival and satisfactory growth.
Ausubo was found on each of six permanent plots measured since the mid-1940's in the Luquillo Mountains of Puerto Rico. On plots that normally contain 40 to 50 species per 0.4 hectare (1 acre), ausubo ranked 5th in density, and 10th in both basal area and volume (6). Recurrent measurement of all trees on these plots revealed a 30-year chronology of stand dynamics after a hurricane. Ausubo, a primary species, increased in dominance over time, doubling its proportion of stand basal area to 10.7 percent and tripling its stand biomass to 9.1 percent (12). Large size at maturity, a long life cycle, good root development, and tolerance of shade enable ausubo to persist for 300 to 400 years and emerge as one of the canopy species in the Luquillo Forest.
Damaging Agents- Survival is hampered by the very slow rate of seedling growth, and the fact that during this stage ausubo is succulent and eaten by animals (27). The leaves are frequently darkened by a layer of sooty mold that probably reduces the amount of light received. In a study of microfungal populations on ausubo leaves, it was found that a statistically greater number of fungi were present on the leaves at lower levels of the canopy than at mid- and upper-levels (11).
Ausubo tolerates exposure well. Along the north coast of Trinidad, several groups of trees grew in areas exposed to the full force of the northeasterly tradewinds. Marshall (27) observed that even the clearing of a site for the construction of a cabin, leaving numerous large ausubo isolated, apparently had no effect on their survivial.
Some infestations have been observed. In Trinidad, large trees with hollow bases were infested with both termites and a fungus, but it was not determined which agent was the primary cause of infection (27). In Puerto Rico, a canker has been observed that results in the dieback of branches, but the causative agent is unknown (33).
Perhaps the agent most damaging to ausubo is man. In the process of "bleeding" trees to obtain balata gum, trees may be indiscriminately slashed and later die. Sometimes they are felled to obtain the latex.
The heartwood is light red when cut and turns to dark reddish brown when dry. The sapwood is whitish to pale brown. The wood is very hard, strong, fine textured, and heavy, with a specific gravity of 0.85. The wood rates excellent for boring, fair for planing, and poor for turning (21,22,23). It is difficult to air season and shows severe checking and warp if dried too fast (9). The wood finishes very well and resembles mahogany. It is resistant to the dry wood termite, Crytotermes brevis, in Puerto Rico (35), highly resistant to the subterranean termites, Coptotermes niger, Heterotermes convexinotatus, H. tennis, and Nasutitermes corniger, in Panama, but susceptible to marine borers. The wood is also very resistant to white- and brown-rot fungus (7,9,23) and is very durable in contact with the ground (28).
Ausubo is one of the strongest and most attractive commercial woods in Puerto Rico. It is widely used in the tropics for railway sleepers, bridging, heavy construction, furniture, turnery, flooring, violin bows, and billiard cues. Its strength, high wear resistance, and durability qualify the timber for use in textile and pulpmill equipment (9,21,27). Its excellent steam-bending properties make it suitable for boat frames and other bent work (23).
The tree is also tapped for balata gum which is similar to gutta-percha. In some areas, trees have yielded sap for more than 25 years (30). The latex is coagulated by fire or dried in the sun, and souvenirs or novelties are then fabricated (21).
The sap from some of the species within the genus apparentlv can be used as a substitute for cow's milk. The latex has the consistency and taste of cream, but overindulgence in it can result in severe constipation.
No information was found on population differences, races, or hybrids. The genus is pantropical, contains more than 150 species, and is the most important within the Sapotaceae family Ausubo extends from latitude 23' N. to about 18' S. in the American tropics, and it is possible that varieties remain to be described.
Zapote de costa (Manilkara pleeana) (Pierre) Cronq. is a related tree of moist coastal forests known only from Puerto Rico, Vieques, St. John, and Tortola (21). Several other closely related species of Manilkara grow in Central and South America and are confused with M. bidentata (23). Much taxonomic study is needed in the Sapotaceae family, genus Manilkara.