Cellulosic Energy Cropping Systems (Karlen/Cellulosic) || Eucalyptus

9

Eucalyptus

Michael W. Cunningham and Bijay TamangArborGen Inc., U.S.A.

9.1 Phylogeny, Growth, Yield and Chemical Composition

9.1.1 Introduction and Phylogeny

Eucalyptus belongs to the Myrtaceae family and is comprised of more than 700 species.Most Eucalyptus species are native to Australia but a few are also native to New Guinea,Indonesia and Philippines. Corymbia and Angophora are two closely related genera withEucalyptus. These three genera are collectively known as eucalypts, but Corymbia andAngophora have been classified as subgenera of the Eucalyptus genus in the recent taxo-nomic classification [1].

Eucalyptus is one of the most widely planted genera in the world but large scale planta-tions are mostly limited to tropical areas. Eucalyptus plantations worldwide cover a total of17.9 million ha [2]. About 11 million ha are located in Asia while South America has about5 million ha [2]. Eucalyptus has been an attractive species to farmers in developing coun-tries because of its fast growth, straight form, coppicing ability and adaptation to varioussoil types.Out of more than 700 species of Eucalyptus, only about 500 have the potential for

commercial plantation [3]. E. grandis is one of the widely planted species because of its fastgrowth and higher productivity. Eighty percent of the Eucalyptus plantations worldwide arecomprised of E. grandis, E. urophylla, E. camaldulensis, E. globulus, and their hybrids [4].In the United States, there are approximately 50 000 ha of Eucalyptus planted in Florida,California and Hawaii [5]. Major species planted in the United States are E. grandis,E. urograndis (a hybrid between E. urophylla and E. grandis), E. benthamii, E. globulus,E. robusta and E. camaldulensis, but only the former three, as well as E. amplifolia, arecommercially planted in the southeastern states.

Cellulosic Energy Cropping Systems, First Edition. Edited by Douglas L. Karlen.© 2014 John Wiley & Sons, Ltd. Published 2014 by John Wiley & Sons, Ltd.

150 Cellulosic Energy Cropping Systems

Table 9.1 Growth and yield potentials of commercial Eucalyptus species at high density bioenergy planting(2500–3000 trees/ha) in the Southeastern United States.

Species Growth (m/yr) Yield (GMtons/ha/yr) Rotation (yr)

E. urograndis 4.5–7 45–67 2.5–3E. grandis 4.5–6 40–56 2.5–3E. amplifolia 3–5 18–25 4–5E. benthamii 3–5 30–40 4–5

Eucalyptus species have various uses. It is a major source of wood for fuel and con-struction material in developing countries. Some species have been used in windbreaks inagricultural farms to modify microclimate and increase yields [6, 7]. In South America,Australia and South Florida, U.S.A., Eucalyptus is a major windbreak species to managecitrus canker. Lately, Eucalyptus has received wide attention because of its potential tosupply the increasing wood demand from emerging biomass power plants. The pulp andpaper industry has been using Eucalyptus for decades for fiber. Because of its fast growthand early canopy closure, some Eucalyptus species also have the potential to suppress light-dependent invasive species such as cogongrass (Imperata cylindrica) and restore degradedmined sites [8].

9.1.2 Growth and Yield

Commercialization of Eucalyptus species mainly depends on its growth rate and ease ofpropagation. Most species that are commercially available are fast growers that can beeasily propagated, have good form and are adapted to various soil conditions. Growth andyield of Eucalyptus varies from species to species as well as with the geographical area(Tables 9.1 and 9.2). Generally, the faster growing species such as E. grandis, E. urophyllaand E. urograndis, which are usually the ideal species for tropical areas, have higher yields(Table 9.2). On the other hand, these tropical varieties do not tolerate the cold wintertemperatures of subtropical areas. Therefore, their planting range in the United States islimited to South Florida and Hawaii. When these tropical species are planted further north,trees are killed back to the ground during winter months and coppice every year. Even ifthey survive the cold winter, their growth is compromised due to cold stress.

Table 9.2 Mean annual increment (MAI) of someimportant Eucalyptus species.

Species MAI (m3/ha/yr)

E. deglupta 14–50E. globulus 10–40E. grandis 15–50E. saligna 10–55E. camaldulensis 15–30E. urophylla 20–60E. robusta 10–40

Source: [2].

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Figure 9.1 4.5-year-old Eucalyptus urograndis trees near Sebring, Florida. (Photo: C© 2013 ArborGen Inc.;all rights reserved).

ArborGen has genetically engineered E. urograndis by inserting a freeze tolerant gene(Figure 9.1). Results from field trials suggest that the superior line has growth rates andproductivity similar to the conventional base clone, with better freeze tolerance up to about−8 to −9◦C [9]. With this freeze tolerance achievement, the species can be planted as farnorth as N 30.5◦. The U.S. Department of Agriculture’s Biotechnology Regulatory Servicesis currently reviewing the species for deregulation.

9.1.3 Wood Composition

Biomass characteristics are important for both thermal and biochemical conversion andnot all woods have the same properties. Therefore, ideal feedstock must be selected care-fully based on the properties for efficient and higher output. Moisture content, caloricvalue, proportions of fixed carbon and ash content are important for thermal processes(such as combustion, pyrolysis, gasification and torrefaction) while moisture content andcellulose/lignin ratio are important for biochemical processes (such as fermentation andanerobic digestion) [10].The moisture content of Eucalyptus is higher than 50% (wet basis), which usually causes

concerns among processors because it is more than in softwoods and other hardwoods,which are usually between 45 and 50% (Table 9.3). High heating value is comparable toother hardwoods but lower than pine, which is currently the primary species for energy


Table 9.3 Proximate Analysis of some Eucalyptus species.

Species Sample typeMoisture

(% wet wt)Ash

(% dry wt)Volatile matter

(% dry wt)Fixed carbon

(% dry wt)High heating value,

HHV (MJ/kg)

E. salignaa With bark — 1.22 81.2 18.4 19.4E. robustab With bark 56.2 1.26 79.9 18.9 19.7E. urograndisb With bark 54.4 0.84 82.7 16.5 19.4E. globulusb With bark 50.6 1.1 86.5 12.4 18.6E. grandisb With bark 51.9 0.72 84.8 14.5 19.3

aBiomass Feedstock Composition and Property Database (http://www.afdc.energy.gov/biomass/progs/search1.cgi).b[11].

wood exported from the southeastern United States in the form of pellets. Bark is the majorsource of ash in woody biomass. High ash content along with the presence of metals such assilicon can cause fouling and slagging at higher temperatures [10, 12]. This can significantlyreduce the efficiency of power plants and increase operational costs. Ash content of woodybiomass is less than 2%, whereas in grass species it can be as high as 5–7%. Ash contentin Eucalyptus wood is approximately 1% (Table 9.3), but it can be further lowered byexcluding bark.Another chemical that is of major concern in woody biomass is chlorine. It is a corrosive

element and in high concentrations in biomass can impact operations due to corrosion [12].Corrosive action of chlorine can shorten the life of expensive equipment such as furnacesand boilers, requiring earlier replacement. Though short rotation woody crops are usuallycredited with higher chlorine content, study results show that chlorine content inEucalyptusis usually less than 1% (Table 9.4).Available data on chemical composition ofEucalyptuswood aremostly limited to pulping

characteristics because of its wider use in the pulp and paper industry. With its potential tobe used in the emerging bioenergy markets, other chemical properties are currently beingstudied (Table 9.5). Eucalyptus wood tends to have higher cellulose compared to otherhardwoods. Compared to aspen, up to 9%more lignin has been recorded inEucalyptus [14].Access to sugar in lignocellulose biomass is still a challenge due to recalcitrance of cell wall[15] but, with appropriate pretreatmentmethod under ideal conditions,Eucalyptuswood canbe converted to biofuel [13, 16, 17]. Using biotechnology, lignin content can bemanipulatedin plants to increase sugar release. The U.S. Department of Energy’s National Renewable

Table 9.4 Ultimate Analysis (% dry wt) of some Eucalyptus species.

Species Sample type C H N S O Cl

E. salignaa With bark 49.89 5.71 0.05 0.01 42.29 —E. robustab With bark 52.57 5.81 0.35 0.03 39.89 0.09E. urograndisb With bark 51.96 5.86 0.31 0.02 40.92 0.09E. globulusb With bark 51.95 5.96 0.30 0.02 40.61 0.06E. grandisb With bark 51.26 5.76 0.30 0.02 41.90 0.04


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Table 9.5 Chemical composition of Eucalyptus wood.

Species Sample type Total lignin (%) Arabinan Xylan Manan Galactan Glucan

E. salignaa With bark 26.9 0.3 10.4 1.2 0.7 48.1E. urograndis Without bark 28.0 0.3 10.3 0 0.8 38.8E. grandisb Without bark 32.4 0.3 11.4 0.3 0.9 39.7E. amplifoliab Without bark 34.5 0.4 11.1 0.5 1.3 37.4


Energy Laboratory study using ArborGen’s lignin-modified Eucalyptus (with only half thelignin content compared to unmodified plants) shows that low-lignin Eucalyptus can releaseup to 99% of sugar whereas conventional unmodified plants release only up to 40–50%.

9.2 Cultural Practices

9.2.1 Establishment

One of the reasons why Eucalyptus has received so much attention lately is because of itspotential to grow in marginal land. Eucalyptus grows best in well drained soils and highsoil moisture can reduce tree growth [18]. In areas where soil is not well drained, trees canbe planted on beds. Compared to conventional forestry plantations, Eucalyptus plantationsrequire intensive site preparation. This can increase establishment cost but it is usuallycompensated by high crop yield and multiple coppice crops from the same planting.

Eucalyptus planting stock is almost exclusively produced as containerized seedlings.Containers are usually 100–150 cm3 in volume and the trees are produced in 3–4 months.Tropical species such as E. grandis, E. urograndis and E. saligna can be propagated easilyusing rooted cuttings so that clonal varieties can be developed and planted. Cold tolerantspecies such as E. amplifolia, E. benthamii and E. macarthurii are much more difficult topropagate vegetatively and, to date, are almost always reproduced from seed.

Eucalyptus is extremely sensitive to weed competition. Studies show that Eucalyptusseedlings have less tolerance to interspecific competition [19,20]. In E. globulus, the effectof weed competition on tree growth was evident as early as two months after establishment[19].Unlike pine plantations,weed control is, therefore, amust in the first year for successfulestablishment. Pre-emergent herbicide can be applied during site preparation to slow weedgermination followed by directed sprays as needed after planting in the first year. Oust XP R©

is currently used as pre-emergent herbicide for weed control in Eucalyptus planting but caremust be taken while using it in basic soils because of its potential to kill trees. SFM 75 R© iscurrently the only herbicide labeled for Eucalyptus, both for use during site preparation andover-the-top application. Because of its faster growth, crown closure occurs by the secondyear and competition control usually is not needed after that.Preliminary results of collaborative studies between ArborGen and the University of

Florida’s North Florida Research and Education Center on the effectiveness of severalherbicides and their rates on Eucalyptus show that among several herbicides tested, longer


weed control is obtained with pre-emergent Oust XP R© and Clearcast R© (Pat Minogue, per-sonal communication). Several herbicides can be used for competition control inEucalyptusstands but the rate needs to be adjusted depending on the Eucalyptus genotype. Additionalstudies are currently underway to refine herbicide application rates.

9.2.2 Fertilization

In Eucalyptus, nutrient demand is higher in earlier years because of its vigorous growth.As for other plants, nitrogen and phosphorous are two important nutrients for Eucalyptus.A study in E. globulus suggests that nitrogen and phosphorous, which are responsible fortree growth, are important nutrients in the first year and their application in the first yearcan significantly impact growth in the later years, too [21]. In E. grandis, the applicationof phosphorous increased nitrogen and sulfur absorption, significantly improving growth[22]. Though boron is required in small amounts, it is important when trees are growingin marginal lands. Sandy soil usually lacks potassium and must be supplemented throughfertilizer application. Earlier studies suggest that fertilizer application methods (broadcastapplication versus placing fertilizer in a hole next to the seedling) do not have a significantimpact on Eucalyptus seedling growth [23,24], but application timing can have significanteffects on growth [25].

9.2.3 Disease and Pest Control

Because of large commercial plantations, Eucalyptus diseases in South America, Australiaand Asian countries are widely studied and well understood, but information from NorthAmerica is limited. In general, Eucalyptus diseases can broadly be classified into foliardiseases, stem cankers, bacterial wilt and nursery diseases [26]. Economically importantEucalyptus diseases and pests present worldwide and their impacts are discussed in detailin references [26–28].

Eucalyptus longhorned borers (Phoracantha semipunctata and P. recurva), snout beetle(Gonipterus scutellatus), tortoise beetle (Trachymela sloanei) and at least six psyllid specieshave been reported from California [29]. Galls of blue gum chalcid (Leptocybe invasaFisher and LaSalle) were found for the first time in North America in the stem and leavesof Eucalyptus trees in Florida. The species is currently distributed in Broward, Palm Beach,Glades, Hendry, Lee and Dade Counties in Florida [30]. In 2001, the red gum lerp psyllid(Glycaspis brimblecombei Moore) and the Eucalyptus psyllid (Blastopsylla occidentalisTaylor), which are native to Australia, were also reported in the Orlando, Florida area forthe first time. They have also been recorded in California [31]. Eucalyptus stem canker hasalso been observed in Florida.

9.2.4 Harvest Management (Cutting Height, Season, and Frequency)

Any forest tree harvester that leaves a clean cut stump can be used for harvesting Eucalyptusbut care should be taken not to damage the stump if the plantation is to be managed fora coppice crop. A study in E. globulus shows that coppicing is influenced by lignotuberdevelopment, seedling stem diameter and vigorous growth before felling [32], but other

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factors such as condition of stump, cutting height and harvest season can also impactcoppicing. During harvesting, bark can peel off easily from the stump, thereby reducingthe chances of coppice. Therefore, harvesters with saw heads are recommended rather thanthose with shear heads for Eucalyptus harvest. Care should be taken not to run over thestumps during the harvesting operation.Recommended cutting height is 15–20 cm above the ground. A tall stump increases the

chances of coppice windthrow whereas a low stump reduces the chances of coppicing.Though it is difficult to achieve using commercial harvesters, the cut surface should beslightly angled (if possible) to allow water to drain from the surface easily. This minimizesthe chances of fungal infection on the cut surface.Depending on the species, rotation of Eucalyptus planted in high density bioenergy

plantations can range between 2.5 and 5 years (Table 9.1). There is no specific season forEucalyptus harvest but the spring season is ideal to encourage coppicing during summer.Harvesting during winter months (end of the year) can potentially lower coppice rate.Results from a study of oaks shows that stump mortality decreases when the trees are cutoutside growing season [33].

9.3 Genetic Improvement

Intensive selection and improved silviculture have improved the growth rates. The U.S.Forest Service started genetic improvement of Eucalyptus in the southeastern United Statesin the 1960s. The Forest Service discontinued its program in the early 1980s when mosttests were compromised due to cold weather. The University of Florida later started thegenetic improvement of E. grandis and E. amplifolia. After extensive tests throughout thestate of Florida, four commercial E. grandis cultivars E. nergyTM G1, G2, G3 and G4with exceptional growth rate, freeze tolerance and stem form were released in 2009 [34].Another new clone, G5 has been released recently. All five cultivars have differences inperformance, genetics and wood properties. Four cultivars (G1–G4 cultivars) were plantedat various sites across the state in 2009 and 2010 and produced exceptional growth rates andfreeze tolerance. Work is underway to develop more E. grandis and E. amplifolia cultivars.

E. urograndis has been planted extensively in Brazil by pulp and paper and charcoalcompanies because of the hybrid’s fast growth and excellent wood properties [35]. In theUnited States, E. urograndis is grown only in Hawaii and South Florida due to its tropicalnature. ArborGen has genetically modified E. urograndis to increase its freeze tolerance.Conventional E. urograndis usually can tolerate temperatures as low as −1◦C but thebiotech varieties developed by ArborGen with freeze tolerant gene in them can tolerateapproximately −8 to −9◦C. Field trials were successfully conducted in the southeasternUnited States. The species can now be planted as far north as the Interstate-10 corridor upto East Texas.North Carolina State University, in collaboration with several pulp and paper companies,

began a testing program to identify cold hardy Eucalyptus that could survive winter temper-atures in the southeastern United States in the 1970s [36]. The research project identifiedfour species (E. viminalis, E. macarthurii, E. nova-anglica and E. camphora) with somefreeze tolerance that could survive the fluctuating warm and freezing temperatures in theregion. A series of severe freezes in the mid-1980s destroyed all but a few trees for which


efforts were undertaken to continue a genetics program through vegetative propagation andtransfer of selected trees to amilder climate for seed production [37]. Ultimately that projectwas terminated. Recently, North Carolina State University has renewed its research effortsat developing cold hardy eucalyptus adapted to the United States and a series of speciesscreening trials were planted from Texas to North Carolina. There have been some encour-aging early results with the species E. benthamii. The University and its collaborators arenow looking at combining the cold tolerance of some species with the rapid growth, easeof propagation and wood properties of tropical species in a hybridization project (SteveMcKeand, personal communication).Westvaco Corp. began the testing of E. benthamii in the United States in the early

1990s. Several of the earlier trials are still present in the states of South Carolina, Gero-gia, Florida and Texas. Seed collected from a mother tree in a South Carolina test hasshown an exceptional potential of E. benthamii for genetic improvement (Figure 9.2).Trees planted near Chatom, Alabama had exceptional growth and tree form. Average treeheight was about 12 m in three years. ArborGen has acquired seeds of 100 E. benthamiifamilies from Australia’s Commonwealth Scientific and Industrial Research Organiza-tion (CSIRO); these are currently being tested in Florida, Alabama and Texas. Thoughthere are significant differences between families, early growth results are exceptional(Figure 9.3). Tree size and form within a family are uniform. Some families were 2.5 mtall in seven months. The goal is to convert the tests to commercial seed orchards in thenear future.

Figure 9.2 3.5-year-old E. benthamii trees near Chatom, Alabama. Average tree height was 12 m. (Photo:C© 2013 ArborGen Inc.; all rights reserved).

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Figure 9.3 7-month-old E. benthamii progeny test at Bellamy, Florida. (Photo: C© 2013 ArborGen Inc.; allrights reserved).

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