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Home , Dendrology, Eucalyptus grandis, Eucalyptus robusta, Melaleuca quinquenervia

Eucalyptus robusta Sm. Robusta Myrtle James P. King and Roger G. Skolmen

Robusta eucalyptus, , is native Hawaii (fig. 1). The has been studied in to a narrow coastal area in southeastern . as a source of (8). The species is widely adaptable and has been intro- duced into many tropical, subtropical, and warm- Habitat temperate climates including Puerto Rico, southern Florida, coastal California, and Hawaii. It is natural- Range and Climate ized only in southern Florida and Hawaii. Commonly called swamp- in Australia, it is usually Robusta eucalyptus is native along the Australian called robusta eucalyptus in the United States (2,16), coast of and southeast . and beakpod eucalyptus in Puerto Rico (17). It is found mainly in swamps and on the edges of The species was originally introduced as a can- coastal lagoons and rivers where it is subject to didate for timber production, fuel, watershed protec- periodic flooding (5,9). The mean maximum tempera- tion, and windbreaks. By 1960, more than 4650 ha ture in the hottest month is 30” to 32” C (86“ to 90” (11,500 acres) of were established in F); the mean minimum of the coldest month is about 3” to 5” C (37” to 41” F). Throughout the native range, from 5 to 10 light frosts occur each year (6). In Hawaii, robusta eucalyptus grows well from near sea level to 1100 m (3,600 ft) where annual rainfall ranges from 1000 mm (40 in) to 6350 mm ir in) and temperatures rarely if ever reach freez-

Robusta eucalyptus in Florida grows mainly in the southern portion of the State where frosts may occur annually. Mean annual rainfall averages 1320 mm (52 in) with 70 to 80 percent of rain falling during the May to October wet season. In Puerto Rico the species makes its best growth in mountain regions about 460 m (1,500 ft) where annual rainfall averages 2540 mm (100 in) (17). In southern California and along coastal northern California, plantings of robusta eucalyptus have been subject to several unseasonal cold spells (11,20,21) where temperatures reached -9” C (16” F). In every instance severe foliage damage was initially observed (more than 80 percent of the crown foliage killed), but the stems recovered within 3 months. Although robusta eucalyptus can recover from oc- casional severe frost damage, the limiting variable in its distribution seems to be low temperature. If the temperature drops below -9” C (16” F) annually, in- troduced robusta eucalyptus will seldom be success- ful. In Yunnan Province, China, -7” C (19” F) damaged robusta eucalyptus, but to a lesser extent than E. globulus (4). Figure 1-Robusta eucalyptus is used to produce sawtimber in Hawaii. Soils and Topography

Robusta eucalyptus grows well on a variety of The authors are Research Geneticist (retired) and Principal Sil- soils, ranging from its native intermittently flooded viculturist (retired), Pacific Southwest and Range Ex- sites (6,9) to the hot summer-dry soils of California’s periment Station, Berkeley, CA. Central Valley (11).

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In Florida, typical soils are poorly drained, acid, Florida, California, and Hawaii, have been ob- fine sands with hardpans at depths proportional to served to by the end of the third growing the depth of the seasonally high water table. Robusta season. The peak flowering season in Florida is from eucalyptus does best on the least poorly drained of September to November (71, and the peak season in these soils, which are typical of arenic and aeric California is from January to March (II). In Hawaii haplaquods of the order Spodosols (7). and more tropical areas, new may appear at Most robusta eucalyptus in Hawaii are planted on almost any time of the year and individual trees sites considered too steep for agriculture-usually occasionally bloom year-round. slopes of 10 to 20 percent. On the older islands of The trees flower with 5 to 10 flowered axillary Kauai, Oahu, Molokai, and Maui, trees were planted . The and are fused into a predominantly on Oxisols and Ultisols. On the caplike structure (operculum) that drops off the tip youngest island, Hawaii, plantings are mainly on of the flower at anthesis. The eucalypts are, in Histosols and Inceptisols. All these soils are formed general, protandrous (23). The showy part of the on basaltic parent materials, either volcanic ash or cream-colored flower is actually the numerous lava rocks. Soils are low in nitrogen and phosphorus filamentous that surround the . and often strongly acidic. The lava substrate may be The is a vase-shaped dark green 12 in either almost continuous sheets or in highly frac- to 15 mm (0.5 to 0.6 in> long that contains many tured porous clinkers. Soil drainage, therefore, varies small . The fruit ripens 5 to 7 months after from very poor to extremely rapid in very short dis- flowering. tances. Production and Dissemination-Seeds of Associated Forest Cover robusta eucalyptus are small and like all eucalyptus contain no . The viable seed is difficult to In its native range the species is dominant in some separate from the chaff (unfertilized or aborted areas and is often found in pure stands. Associated ) in the ripe flower capsules. There are 200 to trees may include kinogum eucalyptus (Eucalyptus 400 viable seeds per gram (5,700 to 11,3OO/oz) of seed resinifera), bloodwood eucalyptus (E. gummifera), and chaff (12). forest redgum eucalyptus (E. tereticornis), longleaf is largely by wind and may begin casuarina (), and various species of within 6 weeks after the seed capsule ripens. In (8). Florida, most trees retain seeds in closed capsules for Throughout the 1930’s, when most of the more than 1 year after ripening (7). planting was done in Hawaii, robusta eucalyptus was used to overplant failed plantations. Consequently, Seedling Development- is epigeal because robusta eucalyptus could survive on a wide (12). Robusta eucalyptus in Florida has occasionally variety of sites, it is found in many mixed plantings. reproduced naturally around abandoned homesteads, Some common associates with robusta eucalyptus probably following fire dn the native range. The seed are saligna eucalyptus (Eucalyptus salignu), tallow- source was usually an old amenity planting of robus- eucalyptus (E. microcorys), melaleuca ta eucalyptus and the seedlings outgrew the dis- (), horsetail casuarina turbed native vegetation. The species does not invade (Casuarina equisetifolia), and silk- (Grevilla recently abandoned agricultural fields because of the robusta). Treefern (Cibotium spp.) is also quite com- more intense competition from weeds (7). mon in the understory of planted stands. One report Most robusta eucalyptus stands in Florida are refers to a pure stand of robusta eucalyptus being being established through the planting of container- (Podocar- heavily invaded by Javanese podocarpus grown stock. Seedlings in Florida need several pus cupressinu). On wetter sites on the island of months to grow into frost-hardy saplings before Hawaii, robusta eucalyptus stands often develop a facing their frrst frost. Early spring planting would dense, almost impenetrable, understory of strawber- be ideal, but soil moisture is deficient until summer (Psidium cattleianum). ry guava rainfall begins. Thus mid-June through mid-August is the recommended planting period (7). Life History Most robusta eucalyptus stands in Hawaii have been established ai single species plantings and, Reproduction and Early Growth after or other disturbance, regenerate as pure stands of coppice and seedlings. Robusta Flowering and Fruiting-Robusta eucalyptus eucalyptus has recently been used in plan- has perfect flowers that are insect pollinated. In tations. These were all made with container-grown

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seedlings to assure the rapid early start needed to metto prairie site. Within this planting, a system of stay ahead of the wide variety of competing, aggres- inventory plots was established to develop the data sive vegetation (25). After planting, container-grown needed to determine optimum rotation length, ex- seedlings in Hawaii grow almost 30 cm (12 in> per pected yields, and other management guidelines. Al- month for the first few years. though the planting is considered seriously under- stocked with 786 trees per hectare (318 trees/acre), Vegetative Reproduction-The majority of new measurements at 10.25 years estimate a mean an- stems in logged stands of robusta eucalyptus are of nual yield of 16.7 m3/ha (238 ft3/acre). Mean height coppice origin. These coppice arise from dor- of all stems was 16.6 m (54.5 ft) and height of mant in the cambium of the stump. All parts of dominant class trees only was 21.3 m (70 ft>. Stand the stem surface under the bark contain dormant volume in 1979 was 172 m3/ha (2,458 ft3/acre) (7,18). buds that sprout rapidly after crown injury. Planted trees in Puerto Rico have reached 27.4 m Robusta eucalyptus is one of the Eucalyptus (90 R) in height and 41 cm (16 in) in d.b.h. in 15 species that produces lignotubers. A lignotuber con- years (17). Coppice stands often outproduce seedling sists of a mass of vegetative buds and contains sub- stands. A lo-year-old coppice stand in Hawaii stantial food reserves. It begins forming in the axils produced 140 m3/ha (2,000 ft3/acre), while an ad- of the cotyledons and the first three pairs of the jacent 12-year-old seedling stand yielded only 96 seedling . Eventually these organs are over- m3/ha (1,372 ft3/acre) (3). grown by the main stem and remain as tuberous bulges just above the crown. Rooting Habit-The most distinctive charac- When robusta eucalyptus is logged, therefore, the teristic of the rooting habit of robusta eucalyptus in source of the coppice is usually the dormant buds in Hawaii is the tree’s ability, in moist areas, to initiate . the stem cambium surrounding the stump. But if the adventitious from buds on the stem at heights entire stem is killed through fire, or in young seed- of 6 to 12 m (20 to 40 ft) (fig. 2) (13). These roots lings through grazing, new coppice shoots may arise grow downward through the moist bark and into the from the lignotubers (23). In a Florida test, robusta soil. As the root grows in diameter, it sometimes eucalyptus proved to be less influenced by breaks free from the soft bark and appears as an season of cutting than either E. grandis or a hybrid aerial root. The lower stems of occasional robusta E. grandis x robusta, but was reduced during the hot, eucalyptus become completely encased in an inter- dry summer (26). woven mass of these aerial roots, some of them 20 No rooted cuttings of robusta eucalyptus have been cm (8 in) in diameter (14). The species rarely dis- used on a commercial scale, but cuttings taken from plays this habit in its native range or in more young seedlings and young coppice shoots have been temperate climates. Adventitious roots, however, successfully rooted (10). have been noted on a robusta eucalyptus in the Syd- ney Botanical Garden in Australia, and near Rio de Sapling and Pole Stages to Maturity Janeiro (15). Although some layering from the stem may occur as noted earlier, most roots originate Growth and Yield-In 1960, a study in eight below the lignotubers and occupy the entire available different Hawaiian plantations of robusta eucalyptus soil profile on well-drained sites. Robusta eucalyptus gave the following growth data for plantations at is usually quite windfirm on deeper soils and is often elevations ranging from 395 to 730 m (1,300 to 2,400 used for windbreaks in Hawaii. ft), and trees aged 23 to 38 years, with 358 to 642 trees per hectare (145 to 260/acre) larger than 28 cm Reaction to Competition-Robusta eucalyptus (11 in) in d.b.h. (14,22): is classed as intolerant of shade. Where planted in alternate rows with saligna eucalyptus it is invariab- Basal area: 51 to 184 m2/ha (220 to 800 R2/acre). ly overtopped, suppressed, and usually dies within 30 Height of dominants: 28 to 55 m (93 to 179 ft). years. In Hawaii, robusta eucalyptus is planted on Mean annual growth per stand: 7 to 48 m3/ha prepared sites and usually grows faster than weedy (100 to 685 ft3/acre). competitors invading the site. On extremely refrac- Mean annual growth for all eight stands: tory sites robusta eucalyptus is considered the 26 m3/ha (370 ft3/acre>. species of last resort because of its remarkable ability to survive and grow. One of Florida’s first eucalyptus plantations of operational scale established with genetically im- Damaging Agents-Robusta eucalyptus is proved seedlings was established in 1972 on a pal- remarkably free of serious insects or diseases when

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grown in the United States. Cylindrocladium planting concentrated on soils or fractured bedrock scoparium has caused serious losses of seedlings in where roots can penetrate to greater depths. Florida (1). However, this fungus can now be success- In Florida, robusta eucalyptus plantings at about fully controlled by fumigation of soil and containers age 5 may develop a condition called “robusta with methyl bromide before sowing and a followup breakup.” Patches of young trees may develop a bend treatment with benomyl spray. The major cause of in the main stem or on primary branches. Breakage damage to robusta eucalyptus stands in Hawaii is may also occur along the main stem or primary wind (14). Violent windstorms have snapped stems branches, and the wood at the point of breakage may and uprooted trees. Uprooting damage can be par- appear dry and brash. No primary pathogens or ticularly severe when stands are established in shal- pests have been associated with this breakage. Minor low soils overlaying a solid mantle of lava rock. element deficiencies are suspected but are not proven Naturally, such shallow soils should be avoided and as the cause. Adjacent stands of rosegum eucalyptus () appear unaffected (7).

Special Uses

Robusta eucalyptus has found use in urban and as farm windbreaks because of its dark shiny leaves and its generally dense crown. Twigs and branches continually die off and fall to the ground, however, so that the tree is rather hazardous for use in parklands, campgrounds, or even gardens. On the island of Kauai, an older roadside planting of robusta eucalyptus, though most attractive, is main- tained at a high cost for road cleanup.

Genetics

Population Differences

We know of no published data on population differen- ces in robusta eucalyptus. Studies (see “Races”) using seed collections from Australia could be suitable for grouping and analyzing by particular provenances, but such analyses have not been reported.

Races

In 1975, in southern Florida established a genetic base population of 352 collections of Eucalyptus robusta from individual selected trees in Australia, advanced generation families from two previous generations of selection in Florida, as well as selections from Florida’s naturalized stands. This base population was subsequently selected and rogued to form a seedling seed orchard that produces seeds of a bona fide land race of E. robusta for southern Florida. This seed orchard was also a source of genetic material for an effort to develop E. grandis and E. robusta hybrids adapted to Florida conditions (7,19).

Hybrids

Figure Z-A 95-year-old robusta eucalyptus near Honolulu, HI, Several natural hybrids involving Eucalyptus showing well-developed adventitious roots high on the stem. robusta have been reported (24). All of the known

316 Eucalyptus robusta

interspecific hybrids are between E. robusta and 12. Krugman, Stanley L. 1974. Eucalyptus L’Herit Eucalyptus. In other species of the subgenus Symphomyrtus. Seeds of woody in the United States. p. 384-392. C. S. Several have been assigned recognized botanical Schopmeyer, tech. coord. U.S. Department of Agriculture, names. They are E. botryoides var. platycarpa (E. Agriculture Handbook 450. Washington, DC. botryoides x robusta), E. grandis var. grandiflora (E. 13. Lanner, Ronald M. 1966. Adventitious roots of Eucalyptus grandis x robusta), E. longifolia var. multiflora (E. robusta in Hawaii. Pacific Science 20:379-381. longifolia x robusta), E. kirtoniana (E. robusta x 14. LeBarron, Russell K. 1962. Eucalypts in Hawaii: a survey of tereticornis), E. patentinervis, E. insizwaensis (E. practices and research programs. U.S. Department of robusta x globulus, probably), and an unnamed Agriculture, Miscellaneous Paper 64. Pacific Southwest hybrid (E. robusta x saligna, probably). Forest and Range Experiment Station, Berkeley, CA. 24 p. 15. LeBarron, Russell K. 1981. Personal communication. USDA Forest Service. Literature Cited 16. Little, Elbert L., Jr. 1978. Important forest trees of the 1. Barnard, E. L. 1984. Occurrence, impact, and fungicidal United States. p. 55-58. U.S. Department of Agriculture, control of girdling stem cankers caused by CyZindrocZadium Agriculture Handbook 519. Washington, DC. scoparium on eucalyptus seedlings in a south Florida nursery 17. Little, Elbert L., Jr., and Frank H. Wadsworth. 1964. (Eucalyptus grandis, Eucalyptus robusta, benomyl, chlorothalonil, Common trees of Puerto Rico and the Virgin Islands. U.S. copper hydroxide). Disease 68(6):471-473. Department of Agriculture, Agriculture Handbook 249. 2. Bryan, L. W., and Clyde M. Walker. 1966. A provisional Washington, DC. 548 p. checklist of some common native and introduced forest plants 18. Meskimen, George. 1980. Growth and yield in south Florida’s in Hawaii. U.S. Department of Agriculture, Miscellaneous oldest eucalyptus plantations. Paper prepared for the 1979 Paper 69. Rev. Pacific Southwest Forest and Range Eucalyptus Workshop, Bainbridge, Georgia. (On file at USDA Experiment Station, Berkeley, CA. 34 p. Forest Service, Lehigh Acres, FL.) 8 p. 3. Buck, Michael G. and Roger H. Imoto. 1982. Growth of 11 19. Meskimen, George, and E. C. Franklin. 1984. Hybridity in introduced tree species on selected forest sites in Hawaii. the Eucalyptusgrandis breeding population in Florida. USDA USDA Forest Service, Research Paper PSW-169. Pacific Forest Service, Research Paper SE-242. Southeastern Forest Southwest Forest and Range Experiment Station, Berkeley, Experiment Station, Asheville, NC. 15 p. CA. 12 p. 20. Metcalf, Woodbridge. 1961. Progress with eucalyptus in 4. Chen, Binglin, and Junta0 Yang. 1987. Frost injury of North America: United States mainland. Section of USA Eucalyptus associated with an unusually cold winter in Yunnan Province. In Plant cold hardiness. p. 361-362. Alan Report for Second World Eucalyptus Conference. August R. Liss, Inc., New York. 1961, Sao Paulo, Brazil. FAO, Rome. 18 p. 5. Food and Agriculture Organization of the United Nations. 21. Munns, F. N. 1918. Relative frost resistance of eucalypts in 1979. Eucalyptus for planting. FAO Forestry Series 11. Rome, southern California. 16:412-428. Italy. 677 p. 22. Pickford, G. D., and R. K. LeBarron. 1960. A study of forest 6. Franklin, E. C. 1977. Yield and properties of pulp from plantations for timber production on the island of Hawaii. eucalypt wood grown in Florida. TAPPI 60(6):65-67. USDA Forest Service, Technical Paper 52. Pacific Southwest 7. Geary, Thomas F., George F. Meskimen, and E. C. Franklin. Forest and Range Experiment Station, Berkeley, CA. 17 p. 1983. Growing eucalypts in Florida for industrial wood 23. Pryor, L. D. 1976. of the eucalypts. The Institute of production. USDA Forest Service, General Technical Report Biology’s Studies in Biology 61. Edward Arnold Ltd., London. SE-23. Southeastern Forest Experiment Station, Asheville, 82 p. NC. 43 p. 24. Pryor, L. D., and L. A. S. Johnson. 1971. A classification of 8. Hall, Norman, R. D. Johnston, and G. M. Chippendale. 1975. the eucalypts. Australian National University, Canberra. Forest trees of Australia. Forestry and Timber Bureau, 102 p. Canberra, Australia. 334 p. 25. Schubert, Thomas H., and Craig D. Whitesell. 1985. Species 9. Hartney, V. J. 1980. Vegetative propagation of the Eucalypts. trials for biomass plantations in Hawaii: a first appraisal. Australian Forestry Research 10:191-211. 10. Kelly, Stan. 1969. Eucalypts. (Text by G. M. Chippendale and USDA Forest Service, Research Paper PWS-176. Pacific R. D. Johnston.) Thomas Nelson Ltd., Melbourne, Australia. Southwest Forest and Range Experiment Station, Berkeley, 82 p. CA. 13 p. 11. King, James P., and Stanley Krugman. 1980. Tests of 36 26. Webley, 0. J., T. F. Geary, D. L. Rockwood, C. W. Comer, and eucalyptus species in northern California. USDA Forest G. F. Meskimen. 1986. Seasonal coppicing variation in three Service, Research Paper PSW-152. Pacific Southwest Forest eucalypts in southern Florida. Australian Forest Research and Range Experiment Station, Berkeley, CA. 6 p. 16(3):281-290.

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