Didymopanax morototoni (Aubl.) Decne. & Planch.
Araliaceae -- Ginseng family
L. H. Liegel
Yagrumo macho (Didymopanax morototoni) is a well-known pioneer species throughout the tropical Americas. In commerce, the common name is morototo or matchwood because the wood is used for match splints in several countries. The light weight wood is also substituted for certain grades of balsa.
Yagrumo macho is the most widely distributed species within the genus Didymopanax. The range is extensive, roughly from latitude 17° N. to 25° S., and covers wet and moist forests of the West Indies, from Cuba to Trinidad, and continental tropical America from the States of Oaxaca and Veracruz in Mexico, through Colombia, Venezuela, the Guianas, Brazil, and Argentina (4,12,15,23,25,26,33). The species was introduced to Jamaica and has been planted in southern Florida. In Puerto Rico it is quite common, growing in over half of the municipalities and in 8 of 13 State Forests, but it is not common anywhere else in its range. In Panama it is reportedly more abundant on the Pacific side than on the Atlantic side. Local or regional range maps are known only for Colombia and Puerto Rico (13,16,28).
In Puerto Rico yagrumo macho grows in Subtropical Moist, Subtropical Wet, and Subtropical Rain Forest life zones (10). Mean annual temperatures in these life zones range from 24° to 26° C (75° to 79° F), 22° to 24° C (72° to 75° F), and 22° to 23° C (72° to 73° F) with mean annual precipitation of roughly 1500, 3000, and 4000 mm (60, 120, and 160 in), respectively. Elsewhere, yagrumo macho grows in similar life zones, and mean annual precipitation may exceed 5000 mm (200 in) in some parts of the range, as in Colombia (28).
Yagrumo macho is not exacting in soil requirements. Therefore, it grows well on a variety of soils, especially those that have been abandoned after agricultural use. In Trinidad, stands are found on flat areas having deep, bleached sands (Entisols) and on gently undulating areas having outcrops of acidic clays (Ultisols or Inceptisols) (2,19). In Puerto Rico the species grows most commonly on either deep or shallow acid clays (Ultisols and Inceptisols) in the mountains or on calcareous soils (Mollisols) in the "haystack" (mogote) limestone hills.
Although yagrumo macho grows on flat areas in Puerto Rico, particularly near streams, it is more predominant in upland dissected terrain (17) from 100 to 900 m (330 to 2,950 ft); slopes are usually 45 percent or more. On the western end of Puerto Rico, it grows almost at sea level (21). The highest elevations reported for yagrumo macho are in Colombia, where it can be found from 500 to 1700 m (1,640 to 5,580 ft) (28).
Throughout its range yagrumo macho is a common species in secondary forests, in natural or man-made openings in mature forests, or along roadsides and river banks. In Puerto Rico's Subtropical Wet Forest it is often associated with yagrumo hembra or trumpet-tree (Cecropia peltata) and guano or balsa (Ochroma pyramidale), which are also fast-growing, large-leafed successional species having similar physiognomies (10). In openings caused by blowdowns it is also associated with tabonuco (Dacryodes excelsa), the mature component in natural remnants of the Subtropical Wet Forest in Puerto Rico.
In the State of Oaxaca, Mexico, yagrumo macho grows with other thicket species like pegoge (Tabernaemontana arborea), mata-raton (Gliricidia sepium), Vernonia patens, Acacia globulifera, camasey (Miconia spp.), Belotia cambellii, and cerezo (Cordia glabra) (32). Three locally important and associated hardwood species in Trinidad are gommier (Protea insigne), Sterculia caribaea, and serette (Byrsonima spicata) (2). In Venezuela yagrumo macho and yagrumo hembra form a transition zone between guaba (Inga spp.) stands growing along the rivers and high forest stands of Parkia pendula occurring further inland (34). In the Bajo Atrato region of Colombia it is associated with Simarouba spp., boxwood (Jacaranda copaia), and Schizolobium parahybum (20,22).
Flowering and Fruiting- Yagrumo macho has perfect flowers and reproduces in a yearly cycle. Of 96 trees observed for 14 months between 1976 and 1977 in the Luquillo Mountains and at the Rio Piedras Agricultural Experiment Station in Puerto Rico, 58 flowered mainly from October through December (21). There was significantly less flowering in other months. Minimum sizes of trees producing fruits were 6.4 in (21 ft) tall and 10.2 cm. (4 in) in d.b.h. In Trinidad, flowers have been observed mainly in October but also in April and September (19). information on flowering in other countries is not available, but with yagrumo macho's rather extended range, great latitudinal variation in flowering and fruiting can be expected. Flowers are numerous and grouped at ends of branches into many rounded clusters, from 0.3 to 0.6 in (1 to 2 ft) long. The 5petaled, fine brownish and gray hairy flowers are about 5.0 min (0.2 in) across, with white petals about 1.5 mm (0.06 in) long, and five stamens and two styles (16,21).
Pollination mechanisms have not been studied in detail. Bees of the Rigona and Mellipona genera have been observed on yagrumo macho flowers in Costa Rica. Ants of the Crematogaster genus may also play a role.
It takes approximately I to 2 months for flowers to develop into fruits. Immature fruits are dark green or deep purple. They are fleshy, 4 to 6 min (0. 16 to 0,24 in) long, 7 to 10 min (0.28 to 0.39 in) wide, and about 2 min (0.08 in) thick. Fruits usually contain two and occasionally three oblong and flattened brown seeds, about 5 min (0.2 in) long. Mature fruits are dropped almost every month in Puerto Rico, but production peaks from November through June (21). In Costa Rica fruits mature in January and fall from February through May
Seed Production and Dissemination- Seed production for yagrumo macho is an almost continuous process, as it is for other successional species. Seeds have a hard, impermeable outer coat; they can thus remain on the ground for a long time and still retain viability to germinate when openings in the canopy occur. When seed is collected and taken away from field conditions, the number of viable seeds is quite small and germination is extremely poor. Of over 800 individual seeds collected at one site in Puerto Rico, only 5 were viable (21).
Highest germination percentages recorded were 30 percent after 70 days in Brazil and 35 percent after 40 to 90 days in Costa Rica. In Brazil the seeds were soaked for 9 to 10 hours in an unspecified chemical, covered with a thin layer of soil, and protected from direct sunlight. Seeds in Costa Rica were treated with a 3 percent solution of sodium hypochlorite (21). After germination periods of 52 to 120 days, only 12 of 300 seeds germinated in three trials in Puerto Rico. Several soaking treatments with 9 N sulfuric acid were used. Old records from Trinidad show that treating with unknown plant hormone solutions and human urine aided seed germination.
Some 16 bird species feed on yagrumo macho seed or fruits in Puerto Rico. This may provide a plausible reason why good germination in the field cannot be duplicated in laboratory or nursery conditions. Studies have shown that after seeds are ingested by birds, they are subjected to scarification in the gizzard and chemical treatment by gastric juices in the stomach (20). Although attempts to germinate seeds taken from bird feces have failed in Puerto Rico, they have been successful in Costa Rica. It is also proposed that some species feed only on the outer coat of yagrumo macho seed and others feed on the seed endosperm. Thus dormancy could be broken by mechanical puncturing or breaking of the seed coat. Until further evidence is gathered, it can be assumed that birds play the primary role in germination and dissemination of yagrumo macho seed. In Trinidad, bats also act as dispersal agents (3).
Yagrumo macho seed is unwinged and heavy. Of 341 fruits and 125 individual seeds collected beneath one tree in Puerto Rico, all came from one quadrant around the tree's base.
Seedling Development- Germi nation is epigeous. Few studies document seedling growth of yagrumo macho in either field or nursery conditions. Early growth is fairly rapid and best when seedlings are exposed to direct sunlight. In Brazil, d.b.h. and height mean annual increments (MAI's) were 3.0 cm (1.2 in) and 1.7 in (5.6 ft) for 2-year-old plantations (5). A 7-year-old plantation had mean annual height and d.b.h. increments of 1.7 in (5.6 ft) and 19 min (0.8 in). A 20-month-old plantation in Bajo Atrato region of Colombia, planted at 3- by 3-m (9.8- by 9.8-ft) spacing, had very good form and fine branching, with a branch angle usually greater than 70°. Height and d.b.h. averaged 8 in (26 ft) and 12 cm (4.7 in) (2 0).
An MAI of 5.6 mm (0.22 in) in diameter was recorded in Puerto Rico for 20 individuals, where the initial overbark d.b.h. was mostly between 5 to 15 mm (0.2 to 0.6 in) (table 1). Growth was somewhat irregular when related to size class, perhaps because of crown position and the fact that some trees were exposed to direct sunlight and others were not. Mortality for the 20 individuals was 5 percent in I year and was attributed to vine overgrowth (21).
|D.b.h. classes||Mean annual increment at D.b.h.||Tree sampled|
|10 x 10 m quadrant|
|0.0 to 0.5||0.52||2|
|0.5 to 1.0||0.53||9|
|1.0 to 1.5||0.56||6|
|1.5 to 2.0||0.35||3|
|50 x 50 m quadrant|
|0.0 to 2.5||0.86||5|
|2.5 to 5.0||1.30||10|
|5.0 to 7.5||2.46||18|
|7.5 to 10.0||1.40||2|
|33 x 33 ft quadrant|
|0.0 to 0.2||0.20||2|
|0.2 to 0.4||0.21||9|
|0.4 to 0.6||0.22||6|
|0.6 to 0.8||0.14||3|
|164 x 164 ft quadrant|
|0.0 to 1.0||0.34||5|
|1.0 to 2.0||0.51||10|
|2.0 to 3.0||0.97||18|
|3.0 to 4.0||0.55||2|
Vegetative Reproduction- Yagrumo macho wildings transplant readily and the species apparently reproduces by coppicing (19,22). In Puerto Rico sprouting was seen from stems broken off by wind but not on stems killed by lightning (21). Cuttings were used in Brazil (5).
Growth and Yield- Mature yagrumo macho may reach a height of 30 m (100 ft) and a d.b.h. up to 36 cm (14 in) (6,29). More commonly, as in the Luquillo Mountains of Puerto Rico (17), the tree is of medium height and diameter, 15 to 17 m (49 to 56 ft) and 20 to 22 cm (8 to 9 in). The bole is cylindrical, swollen at the base, and has a ringed appearance. Natural pruning in the lower half is excellent (fig. 1). Yagrumo macho cannot be included in biomass estimations from regression equations because of its unusual umbrella-like crown (8). The outer bark is smooth and gray and the inner bark has a slightly bitter or spicy taste (16). Maximum age is probably between 35 and 50 years (21). Rooting is reportedly superficial.
Growth or yield data for mature trees are scarce since yagrumo macho is harvested for local markets and is seldom grown under intensive plantation conditions. Limited data on diameter growth are available for older stands in Puerto Rico. Ten-year d.b.h. measurements in mature tabonuco forests in the Luquillo Mountains showed an MAI from 1.5 to 4.6 mm (0.06 to 0.18 in) (30). Observed growth differences appeared to be related to crown position, with suppressed trees growing least. Eighteen-year d.b.h. measurements showed MAI rates from 3.3 to 5.3 mm (0.13 to 0.21 in) on three sites (table 2) (9). The highest rate was found at Sabana 4, where yagrumo macho is a component of mature tabonuco forests. When analyzed across all three sites, growth differences between crown classes were not positively correlated with increasing crown dominance. Measurements in the Toro Negro State Forest from 1951 to 1976 showed MAI growth for yagrumo macho at 5 mm (0.2 in) (31).
|Item||Sabana 8||Rio Grande||Sabana 4|
|Mean annual increment|
|Elevation--m||180 to 360||420 to 600||210 to 600|
|--ft||590 to 1,181||1,378 to 1,968||689 to 1,968|
Mean annual d.b.h. growth rates observed in Puerto Rico do not even approach the 10 mm (0.39 in) figure sometimes quoted for mature rain forest tree species in the tropics. They are also surprisingly slow for a reportedly fast-growing successional species. Yet caution should be used in interpreting these data because of the long measurement intervals used that could cancel initial fast growth spurts occurring after successful regeneration was established (table 1).
Data from Puerto Rico for yagrumo macho and yagrumo hembra, also a successional species, show that periodic diameter growth for codominant, intermediate, and suppressed trees is comparable. This suggests that a dominant position is required before good diameter growth is shown. Finally, although periodic d.b.h. growth of older yagrumo macho in Puerto Rico was not related to initial diameter classes, it was statistically lower at lower elevations, where it was 1.9 mm (0.07 in) per year, than at higher elevations, where it was 3.7 mm (0.15 in) per year (9).
Rooting Habit- No information available.
Reaction to Competition- Yagrumo macho is classed as intolerant of shade. When planted in full sunlight it exhibits its best growth and reproduction and may be very aggressive against other species. Over a 2- to 6-year d.b.h. measurement period in tabonuco forests in Puerto Rico (1), MAI of yagrumo macho was 3.3 mm (0.13 in). Two more tolerant species found in the same locality, palo de matos (Ormosia krugii) and ausubo (Manilkara bidentata), averaged 5.1 and 6.6 mm (0.20 and 0.26 in). Other work in Puerto Rico indicates that many species growing in association with yagrumo macho have larger periodic diameter increments, probably because they are more tolerant of shade (31).
Few special silvicultural systems for yagrumo macho are found in existing literature. Some 30 years ago in Trinidad, a policy of "let nature heal herself' was followed when reforesting degraded or poor sites (3). Yagrumo macho was one of 18 timber species whose natural regeneration was allowed to grow under a high shelterwood system (2). In Brazil there are pure yagrumo macho plantations designed to produce wood for match splints (5,27). Because yagrumo macho rapidly colonizes open areas and is intolerant, some sort of selective clearcutting is needed to promote adequate regeneration by natural seeding. After cutting, yagrumo macho is one of the first species to become established. It should then be one of the first to be cut for commercial use, selectively leaving more valuable species to be harvested later in the established rotation cycle.
Damaging Agents- Several agents cause damage or death to saplings or mature trees. The most common is probably wind, which can break off branches or uproot entire trees. Wind damage is most acute on very wet, steep sites where saturated unstable soils cannot provide adequate anchorage for roots. In the Luquillo Mountains, climbers or stranglers like Clusia griesebachiana and morning glory (Ipomoea spp.) are common to wetter sites and have caused branch breakage or death of larger seedlings or saplings.
Yagrumo macho is apparently free from serious diseases in nursery and field conditions, but several insects (Scarabaidae and Pyraustidae) consume either foliage or woody tree material in Puerto Rico. Young trees are sometimes killed by grazing cattle in rural areas. Clearing land for agricultural or other development often causes widespread mortality.
Yagrumo macho's specific gravity is between 0.35 and 0.60. Mechanical and physical properties of the wood are somewhat higher than those of yellow-poplar (Liriodendron tulipifera) (6,14). Yagrumo macho is used for general carpentry and interior construction (18). It is also suited for crates and boxes, utility plywood or core stock, match splints, even particleboard, and could probably be substituted for heavier grades of balsa (16). Felled timber is very susceptible to decay and fungal attack if not converted almost immediately. Penetration and absorption of treating solutions, either in open or pressurized tanks, is fair but can be improved considerably by incising untreated material first. Nonincised posts, cold-soaked for 5 days in a 10-percent solution of pentachlorophenol dissolved in diesel fuel, lasted from 9 to 26 years in graveyard tests in Puerto Rico. Double diffusion treatment with several chemicals gave similar results, but cold-soaking with only a 5-percent solution of pentachlorophenol dissolved in diesel fuel was far inferior, the life expectancy being only about 3 years (7).
Yagrumo macho leaves are used for home remedies in some countries (16). Special uses of the wood in Guyana include drums and canoes (11). Brazil has tested yagrumo macho suitability for ethanol production along with 24 other tree species (24). Yield was 299 liters (79 gal) per ton of raw material, close to the maximum yield of 315 liters (83 gal) per ton registered for Protium spp.
Existing literature shows no references to genetic or tree breeding research for yagrumo macho. Wide natural variation in genetic traits would be expected for yagrumo macho because of its extensive natural range and the fact that it grows in several life zones under varied environmental conditions. Since there are also several other species within the same genus throughout Latin America, undescribed hybrids may exist or might be possible if species were brought together under controlled laboratory or field conditions.