Prosopispallida (Humb. & Bonpl. ex Willd.) H.B.K. Kiawe Leguminosae Legume family

Roger G. Skolmen

Kiawe ( pallida), also known as algarroba or bayahonda, is one of the 44 species of Prosopis recognized. The genus has a confused . Burkart’s revision, used here, assigns the designa- tion f! pallida to the species introduced into Puerto Rico and elsewhere in the Caribbean formerly called P. juliflora. Prosopis glandulosa, mesquite, also formerly included in l? juliflora and four to six other species grow as shrubs or trees over an extensive area of the Southwestern United States and North- ern Mexico (2,7,10). More than 60 700 ha (150,000 acres) of dry kiawe forests in Hawaii are descended from a single tree planted in 1828 at the corner of a church in Honolulu. That year, Father Bachelot, the first Catholic priest in the Hawaiian Islands, planted a tree that he had raised from a he had brought Figure 1-A kiawe, already a large tree when first photographed with him from Paris. The tree was later determined in 1855, that continues to grow in the Kawaiahao Church yard, to be Prosopis pallida. In August 1832, the tree was Honolulu. found to be bearing fruit. By 1840, progeny of the (10 to 49 in) (11). On the Islands of Lanai, Kahoolawe, tree had become the principal shade trees of and Niihau, which are in the lee of larger islands, Honolulu (fig. 1) and were already spreading to dry, kiawe occupies both windward and leeward shores leeward plains on all of the islands (3,8,12). extensively. It is present also as a shrub on some windward coasts of all islands. Habitat Many old kiawe trees have been saved as garden and park trees during land development and have Native Range grown to large sizes with irrigation. Although it is a coastal species, kiawe is defoliated by windblown salt Kiawe is native to the drier parts of , Colom- spray of winter storms (3). bia, and Ecuador, especially near the coast. It is naturalized in Hawaii and Puerto Rico (10). Soils and Topography Climate Kiawe grows well on the soils that form on the arid In Hawaii, kiawe is most common in leeward coas- or semiarid coastal lands of leeward Hawaii (fig. 2). tal areas that have an annual rainfall of 250 to 760 mm (10 to 30 in) and a mean annual temperature of 24” C (75” F) with a range of 13” to 35” C (55” to 95” F). In a California study (6), kiawe trees less than 3 years old survived -2” C (29” F), but were killed at -6.1” C (21’ F). Kiawe rarely extends above 150 m (500 ft) in elevation because higher rainfall and lower temperature give other species competitive ad- vantage. In a few locations, however, it reaches an elevation of about 610 m (2,000 ft). In its native habitat, it is reported to grow from sea level to 300 m (990 ft) in annual rainfall from 250 to 1240 mm

The author is Principal Silviculturist (retired), Pacific Southwest Forest and Range Experiment Station, Berkeley, CA. Figure Z-Typical roadside kiawe trees near Honolulu.

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It is also very tolerant of saline soils (11). The soils of the through the digestive system of an where it grows in Hawaii are primarily Inceptisols, animal. From 10 to 20 light brown seeds per pod are Mollisols, and Vertisols. The Inceptisols are in the encased in a sticky, sugary pulp. Seeds are difficult great group Eutrandepts (reddish-brown latosols) to extract from the pods. It is possible, however, to developed from basaltic rock or ash. The Mollisols obtain seed by running pods through a commercial are Haplustolls (low humic latosols) developed from meat grinder with l-cm (0.4-in) holes (5). There are basaltic material and alluvium. The Vertisols are about 28,500 to 32,000 seeds per kilogram (13,000 to Chromusterts (dark magnesium clays) developed 14,50O/Ib). The seeds can be stored at ambient room from alluvium and coral limestone and Torrerts temperature, protected from insects, for 9 months developed from olivine basalt. These soils are mostly with little loss of viability (18). Germination is im- neutral to moderately alkaline in reaction, frequently proved slightly by scarifying the seeds with hot water stony to very stony, and occupy level to moderately before sowing. Scarification with concentrated sul- steep coastal lands. In the driest locations, such as furic acid for 10 minutes improved germination from the eastern slopes of the Island of Lanai, kiawe is 64 percent (without treatment) to 88 percent (18). confined to the gully bottoms. Elsewhere, it extends Many seeds are destroyed by insect pests. In onto ridges. Hawaii, a black beetle, Mimosestes umicus, bores into the pods that have fallen to the ground (16). In Associated Forest Cover Puerto Rico, a Bruchid weevil attacks seed on the tree, causing seed from green pods on the tree to Kiawe is usually found in association with koa have a germination rate of only 59 percent, yellow haole (Leucaena leucocephala), opiuma (Pithecel- pods on the tree only 40 percent, and pods on the lobium duke), and klu (Acacia farnesiana). It is ground only 6 percent (18). sometimes associated with the native tree, wiliwili (Erythrina sandwicensis), the native shrub, a’alii Seedling Development-Germination is epigeal. (Dodonaea uiscosa), and the introduced shrub, lan- Seedlings are usually found associated with animal tana (Lantana camara). droppings during and after rainy periods. In this highly fertile situation, seedlings grow rapidly, reach- ing 0.3 m (1 ft) in 3 to 4 months. Even in the absence Life History of browsing animals, kiawe reproduces prolifically on abandoned city house lots containing older trees. Reproduction and Early Growth Seedlings in such a situation can grow more than 1 m (3 ft) tall in the first year if rainfall is adequate. Flowering and Fruiting-In Hawaii, kiawe Seedling survival depends primarily on sufficient begins to when 3 to 4 years old. The tree can rainfall during 4 to 6 weeks after germination. The flower at any time of the year and frequently seedlings are also intolerant of shade. twice a year. Usually, it flowers from January to March, but in some years with wet summers it also Vegetative Reproduction-Kiawe stumps often flowers heavily during September and October. The sprout after being cut. Some thornless trees have numerous small perfect flowers are borne in pale been propagated by air-layering of the mature yellow spikes 7 to 10 cm (3 to 4 in) long and about branches, but only on an experimental scale. Kiawe 13 mm (0.5 in> in diameter. Styles protrude from the cuttings can also be rooted under mist (5). corolla just before it opens, but when it is opened the style and the 10 stamens are about the same length. Flowers are insect pollinated. Kiawe is an excellent Sapling and Pole Stages to Maturity honey tree (3). About 6 months after flowering and pollination, Growth and Yield-The oldest kiawe trees in the pods ripen and fall to the ground in April and Hawaii of known age are at the entrance to Punahou July, or in normally dry years, only in July. The pods School in Honolulu. This area was a treeless field in are straight or slightly curved yellowish beans 7 to 1848. In 1918, trees on this site that were about 70 20 cm (3 to 8 in) long by 8 mm (0.3 in) wide; there years old ranged from 61 to 104 cm (24 to 41 in) in are 35O/kg (160/lb) (18). d.b.h. and from 20 to 26 m (65 to 85 ft) in total height (9). This is a relatively wet area for kiawe, with an Seed Production and Dissemination-Pods do annual rainfall of 940 mm (37 in) and abundant not open on drying to release their seed as some groundwater from a nearby spring. other legumes do. Instead, seeds are released either At Waianae, Oahu, an area with 510 mm (20 in) by natural decomposition of the pods or by passage annual rainfall, a tract of kiawe trees of unknown

584 Prosopis pallida

age yielded 226.8 m3 per ha (3,240 R3/acre or 36 and it coppices after cutting, so does not require cords/acre). On Maui, a 2.4-ha (6-acre) area with 380 replanting at each rotation. It is a short-boled, mm (15 in) rainfall yielded 365.4 m3 per ha (5,220 crooked tree even when grown at close spacing and ft3/acre or 58 cords/acre) (9). appears unsuitable for use as a timber tree. In Puerto Rico, on a dry, gravelly site (760 mm or 30 in rainfall), a al-year-old planting had trees 25 to Damaging Agents-Kiawe trees are severely 36 cm (10 to 14 in) d.b.h. and 4.6 to 7.6 m (15 to 25 defoliated by the introduced caterpillar Melipotis in- ft) tall (18). domita but quickly leaf out again after defoliation In Honolulu, the original tree, when measured in (17). They are also sometimes partially defoliated by 1916, at 88 years of age, was 99 cm (39 in) in the Blackburn butterfly, Vaga blackburni, an insect diameter (8). But the champion kiawe tree in Hawaii that usually does more damage to other legumes (16). is at Puako, Island of Hawaii, and measures 130 cm In California, a psyllid, Alphalaroida spp., caused (51 in) d.b.h. and 27.7 m (91 fi) tall (1). leafroll of new leaflets in grown in a glass- In a study of biomass production of other Prosopis house (6). The kiawe roundheaded borer, Placoster- spp. in southern California (5), several species, most- nus crinicornis, infects trees under stress, and ly from South America, were grown for 3 years at 1.2 recently cut firewood, boring under the bark and into m (4 ft) spacing and three levels of irrigation. These the sapwood (18). Carpenter seem to have a trees produced an annual average of 8.5 t/ha (3.8 particular affinity for the sapwood of kiawe fence tons/acre) of fresh biomass. Another study in Texas posts. (19) determined that Prosopis natural stands yielded The tree grows in areas where fire hazard is often 19.3 t/ha (8.6 tons/acre) on deep upland soils and 36.1 extreme. It is usually killed outright by fire and t/ha (16.1 tons/acre) on deep bottom land. burned trees almost never sprout. In Puerto Rico, direct seeding in dry areas (760 mm or 30 in rainfall) gave poor survival, but planting of seedlings produced 67 percent survival despite a Special Uses severe 6-month drought (18). Kiawe is used principally as a cover tree for On windy or dry sites, kiawe grows as a shrub, or erosion control on arid land. As recently as 1915, it a small twisted tree only 3 to 5 m (10 to 16 R) tall. was considered the most valuable tree in Hawaii for It is usually layered where it grows in strong trade a variety of other reasons. Its pods and seed are winds and lies along the slopes as a rounded bush. nutritious fodder. The pods alone contain 9 percent protein and the seeds 34 percent, one of the highest Rooting Habit-The genus Prosopis is noted for levels for any legume. But because the seed coats are its ability to root deeply (10). A Prosopis velutina indigestible, the seeds must be ground, if animals are tree in Arizona was found with roots extending to recover this protein. In 1935, Hawaii shipped more downwards 53 m (174 ft) into the ground (10). Kiawe than 200 tons of kiawe honey. A small honey industry seedlings produce strong, rapidly growing taproots in Hawaii continues to depend on kiawe (3,6,9). that appear to be capable of deep extension and may The wood is extremely hard and heavy. It is used share the deep rooting characteristic common to the directly for fuel and also is made into charcoal. The genus. The species can grow on windy, dry sites, heartwood is durable and kiawe is preferred for fence which suggests that its roots penetrate deeply to posts despite its crooked form. Mesquite, a related reach moisture. Trees on such sites are small. Trees species in the United States, is the traditional wood on coastal plains where abundant, shallow ground- used for boatbuilders’ calking mallets and, in Hawaii, water is available reach large size, but are shallow- kiawe is preferred for cement floats. rooted and subject to windthrow (3,9).

Reaction to Competition-Kiawe is an in- Genetics tolerant tree and is shaded out by faster growing plants on wet sites. On dry sites the grasses, koa Because the entire population of kiawe in Hawaii haole, and opuima, with which it commonly as- is originally from one tree, inbreeding has been in- sociates, remain so sparse that abundant sunlight tensive. One possible recessive characteristic of the reaches the kiawe. population is thornlessness. Although most kiawe No silviculture is practiced with kiawe, but the trees have thorns with strong spines often 2.5 cm (1 species’ characteristics indicate that it could be in) long, an estimated 25 percent of the mature trees managed as a fuelwood crop. It fixes nitrogen, so produce only small, hard stipules rather than long, requires less fertilizer than nonleguminous trees, spikelike spines at the twig nodes. The thornless

585 Prosopis pallida

characteristic has been noted for years, and as early 5. Felker, P. 1980. Screening Prosopis (mesquite) germplasm for as 1937, Hawaii shipped seed from thornless kiawe biomass production and nitrogen fixation. In Proceedings, trees to Cuba, Arabia, Australia, Fiji, and South International Congress for Study of Semi-arid and Arid Zones, January 1980, La Serena, Chile. 21 p. Africa (3). Attempts have been made to breed for 6. Felker, P., G. H. Cannell, and P. R. Clark. 1981. Variation in thornlessness, but have so far been unsuccessful. growth among 13 Prosopis (Mesquite) species. Experimental Thornless trees can be propagated by air-layering of Agriculture 17:209-218. mature twigs (13). Some other Prosopis spp. also 7. Hilu, Khidir W., Steve Boyd, and Peter Felker. 1982. exhibit thornlessness among individuals in the Morphological diversity and taxonomy of California populations (10). Thornlessness can be seen in some mesquites (Prosopis, Leguminosae). Madroiio 29(4):237-254. or all of these other species when they are only 3 to 8. Judd, C. S. 1916. The first algaroba and royal palm in Hawaii. Hawaiian Forester and Agriculturist 13(9):330-335. 4 months old (4). 9. Judd, C. S. 1919. A volume table for algaroba. Hawaiian One report states that Prosopis spp. bear self-in- Forester and Agriculturist 16(3):64-66. compatible flowers (15). This is obviously not true of 10. National Academy of Sciences. 1979. Tropical legumes: Prosopis pallida, or at least of that one individual resources for the future. Report of Ad Hoc Panel of Advisory Prosopis pallida originally introduced into Hawaii. Committee on Technology Innovation. National Academy of Another report mentions that in 1920, the U.S. Sciences, Washington, DC. 331 p. Department of Agriculture’s Experiment Station in 11. National Academy of Sciences. 1980. Firewood crops. Shrub Honolulu had imported seed and was growing seed- and tree species for energy production. Report of panel on firewood crops. National Academy of Sciences, Washington, lings of a number of other Prosopis spp. in an at- DC. 237 p. tempt to determine the identity of the tree common 12. Nelson, R. E., and P. R. Wheeler. 1963. Forest resources of to Hawaii by comparison (14). No record exists of the Hawaii-1961. USDA Forest Service, Pacific Southwest Forest disposition of these seedlings, but a possibility exists and Range Experiment Station in cooperation with the that they may have been outplanted. No hybrids are Hawaii Department of Land and Natural Resources, Division known in Hawaii, however. of Forestry. Berkeley, CA, and Honolulu, HI. 48 p. 13. Pung, Ernest. 1979. Personal correspondence. Hawaii In addition to kiawe, at least five other Prosopis Division of Forestry and Wildlife, Hilo. species deserve consideration for use in arid lands for 14. Rock, J. F. 1920. The leguminous trees of Hawaii. Hawaiian firewood, forage, and cover (10). One of these, Sugar Planters’ Association Experiment Station, Honolulu, , is the backbone of the Arizona nursery HI. 234 p. shade tree industry (4). 15. Simpson, B. B. 1977. Breeding systems of dominant perennial plants of two disjunct warm desert ecosystems. Oecologia (Berlin) 27:203-226. Literature Cited 16. Stein, John D. 1981. Personal correspondence. Pacific Southwest Forest and Range Experiment Station, Berkeley, CA, stationed at Honolulu, HI. 1. American Forestry Association. 1974. Champion trees of 17. Tamashiro, M., and W. C. Mitchell. 1976. Control of three Hawaii. American Forests 80(5):26-35. species of caterpillars that attack monkey-pod trees. 2. Burkhart, A. 1976. A monograph of the genus Prosopis University of Hawaii Agricultural Experiment Station, (Mimosoideae). Journal of the Arnold Arboretum 57:216-249, Miscellaneous Publication 123. Honolulu. 4 p. 450-525. 18. Wadsworth, Frank H. 1981. Personal communication. 3. Degener, Otto. 1972. Prosopis chilensis (Molina) Stuntz. In Southern Forest Experiment Station, New Orleans, LA, Flora Hawaiiensis, Books l-4, Family 169a. Privately stationed at Rio Piedras, PR. published, unpaged. 19. Whisenant, S. G., and D. F. Burzlaff. 1978. Predicting green 4. Felker, Peter. 1979. Personal correspondence. Texas A & I weight of mesquite (Prosopis glandulosa Torr.). Journal of University, College of Agriculture, Ringsville, TX. Range Management 31(5):396-397.

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