Pictures of eucalyptus trees

7 Remarkable Facts About Eucalyptus Trees

What do you know about eucalyptus trees? Beyond knowing they’re native to Australia and koala bears love munching their leaves, that is.

When it comes to this magnificent genus of trees commonly called gum trees, there’s a lot to know. On the dull-ish end of the spectrum, we have facts about the word “eucalyptus”. It comes from a combination of Latin (eu meaning “from”) and Greek (kalyptos meaning “covered” and kalyptein meaning “to conceal”) used to describe the seed pod. Good to know but not the kind of info worth sharing at your next dinner party.

Thankfully, there’s more to this millennia-old tree.

Whether you’re a newbie or a eucalyptus expert, read on! You could learn 7 lesser-known and somewhat remarkable facts about eucalyptus trees, like did you know that eucalyptus flooring is a thing? You won’t believe the benefits of eucalyptus flooring!

1. Eucalyptus Flowers Have No Petals

From a distance, the flowers on most species of eucalyptus trees look like fluffy bursts of color, kind of like a dandelion flower gone to seed.

Get closer and you’ll see why. These breathtaking blossoms have no petals. The entire “bloom” consists of hundreds of stamens emerging from a central cone-like bud.

They come in a range of colors including white, bright red, vibrant orange, deep pink, and lime green.

The abundance of stamens translates to an abundance of pollen. And, eucalyptus trees can use as much pollen as possible. They have few natural pollinators because of high concentrations of cineole. (See #3 on this list for more about that). Most often, eucalyptus trees count on the multitude of stamens for self-pollination.

2. Square Stems and Uncommon Leaf Formations

Small branches of eucalyptus trees and shrubs are popular in flower arrangements. Why? In part because of their sturdiness and the visual appeal of their leaf formation.

While most trees have round stems, eucalyptus stems are closer to square. The natural advantage of this shape is unclear, but that doesn’t detract from its beauty.

What also makes the stems and branches of eucalyptus trees compelling is the way the leaves grow. They grow in pairs on opposite sides of the stem. But the neighboring pairs of leaves are at right angles to each other. So a pattern of A-C, B-D, A-C, B-D, etc. emerges where A, B, C, and D are the four sides of the stem.

There are other plants with this kind of leaf formation, but it isn’t common.

3. Cineole: The Secret Ingredient

Eucalyptus essential oil has been used in Indigenous Australian medicine as an antibacterial and anti-fungal agent for centuries. In India’s Ayurvedic medicine, it’s often used in the treatment of respiratory ailments. In 17th century England, it was used to disinfect hospitals.

Why? Because eucalyptus leaves and bark contain high concentrations of cineole.

Cineole is a colorless, liquid organic compound. It’s sometimes also called eucalyptol because there’s so much of it in eucalyptus trees and shrubs. The fragrance of eucalyptus is primarily that of cineole.

We don’t want to sound like a high school chemistry tutorial, so let’s simply say that cineole is the eucalyptus’ secret weapon against predators.

Only the koala bear, ring-tail possum, and a few insects can eat eucalyptus leaves and bark. No other creature, including humans, can withstand the high levels of cineole. In fact, in high concentrations, it’s toxic. That’s why it makes an effective and natural insect repellent.

Clinical research has proven the anti-bacterial, antiseptic, and anti-fungal properties of cineole. Using eucalyptus essential oil in topical wound treatment, skincare, and other disinfecting applications makes sense.

4. Eucalyptus Trees Can Help Prevent Malaria

It’s no secret that eucalyptus trees love water. They thrive in marshy and flooded areas.

That’s why they’re sometimes planted in areas with high malaria rates.

Malaria, a disease found on every continent but Antarctica (another factoid to impress your dinner companions), relies on a specific kind of mosquito for its survival. The malaria parasite lives in female mosquitoes who bite humans. During the bite, the malaria parasite is transferred to the human.

And what do we know about mosquitoes? They love standing water. From swamps to puddles in the backyard, mosquitoes need stagnant water to breed.

In areas of the world with high populations of malaria-carrying mosquitoes, eucalyptus trees are sometimes planted. Not only do they reduce the amount of stagnant water, their secret weapon, cineole, helps reduce mosquito populations.

5. Eucalyptus Trees Can Help Manage Wastewater Issues

Much like using eucalyptus trees to help manage malaria, there’s ongoing exploration into using this remarkable tree to reduce wastewater issues.

In several parts of the world, wastewater carrying heavy metals, bacteria, and other toxins into the groundwater is a concern for agriculture. In response, environmental engineers and agri-forestry professionals plant eucalyptus trees in strategic locations. There’s a wealth of evidence that the eucalyptus absorbs and filters many elements we don’t want in the water used on crops.

While there’s still more research needed to know the right balance of eucalyptus trees to agricultural land, the outlook is promising and is another remarkable fact about the gum tree.

6. Eucalyptus Wood Makes the Best Didgeridoos

Didgeridoos are a long, trumpet-like instrument with a deep history among the Indigenous people of Australia. Traditionally, it’s played during ceremonial dancing and singing. Today, it’s also played for recreation.

But no matter why it’s played, many who know about these things contend that the best didgeridoos are made from eucalyptus wood.

Traditional production involves finding a tree trunk or major branch that’s been hollowed out by termites. The trunk or limb is then cut down, cleaned inside, and stripped of its bark. The hardness of eucalyptus wood helps create pleasing acoustics when played.

7. Eucalyptus Grows Super Fast

One of the reasons it’s an environment-friendly choice is the rate at which the trees grow. Many varieties reach early maturity ten years after planting.

That’s super-fast, compared to other hardwoods, which can take 18-25 years to reach early maturity. Provided they have enough water and are in the right climate, eucalyptus trees are a renewable resource. That’s a remarkable and important fact for the sustainability of the flooring industry and for consumers who want to make better choices for the environment.

Whether you use eucalyptus trees for essential oils, didgeridoos, or flooring, you get value. And in ten years, someone else can also enjoy the benefits of another eucalyptus tree.

So, how many of these 7 facts about eucalyptus trees did you know? Do you use eucalyptus or have it in your home? Let us know in the comments!

If you would like to see a sample of our incredibly beautiful and durable eucalyptus flooring, click on the box below. If you have any questions, please call one of our flooring professionals today at (866) 710-7070.

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The story of our eucalypts

Eucalypts—often called gum trees—are icons of the Australian flora. With more than 800 species they dominate the Australian landscape, forming forests, woodland and shrublands in all environments except the most arid deserts.

Karri and Mountain ash form tall wet forests, mallee species grow in semi-arid regions and snow gums are stunted twisted trees of subalpine regions.

Eucalyptus regnans (Mountain Ash) form tall, dense wet forests. Image adapted from: Pauline Ladiges, with permission.

A few tropical species extend the range of eucalypts north of the continent, with rainbow gum (Eucalyptus deglupta) found in the rainforests of New Guinea, Sulawesi and Mindanao in the Philippines, and White Gum (Eucalyptus alba) on Timor.

Eucalyptus alba (pictured here on Atouri Island, Timor) is native to Australia, and the islands of New Guinea and Timor to Australia’s north. Image adapted from: Pauline Ladiges, with permission.

Evidence from sequencing DNA and the discovery of fossils indicate that the eucalypts have their evolutionary roots in Gondwana, when Australia was still connected to Antarctica. Impression fossils of leaves and fruits with very good detail have been described from Patagonia in South America and dated at 52 million years old. Less well-preserved fossils are known from sites in Australia and even in New Zealand.

Ancient eucalypts were probably similar to some of the current day tropical wet forest species. They would have occurred among or on the edge of ancient rainforest. And as Australia drifted north, they adapted to drier climates, weathered soils and a fire-prone landscapes. As Australia reached southeast Asia the opportunity arose for range expansions to the north, where today we see Rainbow Gum.

Eucalyptus deglupta is native to a number of islands to the north of Australia, including New Guinea, Sulawesi (Indonesia) and Mindanao (the Philippines). Image adapted from: Thomas; CC BY-SA 2.0

The remarkable ability of most eucalypts to quickly re-sprout from dormant buds located under the bark or in lignotubers following damage from drought or fire is a feature that has helped them to survive and dominate the harsher environments that evolved with Australia’s changing climate over the last 30 million years or so.

These Eucalyptus behriana trees have obvious lignotubers at the base of their trunks. Image adapted from: Pauline Ladiges, with permission.

Eucalypts are evergreens. Unlike many northern hemisphere trees that are deciduous in harsh times such as winter, eucalypts have leaves all year. Eucalypts are described as ‘sclerophylls’, meaning ‘hard-leaved’. The leaves are thick, leathery and tough due to lignin, and do not easily wilt. This enables them to survive hot and dry conditions.

After periods of stress, like drought or fire, eucalypts can sprout from dormant buds beneath the bark. Image adapted from: Elizabeth Donoghue; CC BY-NC-ND 2.0

Eucalypts also develop very different leaves as they grow from young juvenile plants to adult trees. Often the juvenile leaves are held horizontally to maximise light absorption but as adults the stalk of the leaf twists and the leaves hang vertically to reduce exposure to high levels of radiation and water loss. The internal anatomy of the leaves also changes.

Many eucalypts, like this Eucalyptus macrocarpa, have juvenile foliage that is quite different to the adult leaves.Image adapted from: Pauline Ladiges, with permisison.

A unique feature of the eucalypts is the caps—called opercula—that cover the flowers when in bud. These caps are the equivalent of the showy petals and sepals of other flowering plant. The flowers themselves don’t have such petals, but display many stamens, often cream coloured, but pink and red in bird-pollinated species. The opercula prevent the flower from drying out and along with oil glands in the tissues, help protect it from insect attack. Evidence that these opercula provide a selective advantage to plants comes from the fact that they’ve evolved independently in different genera—in both the genus Eucalyptus and in genus Corymbia (the bloodwoods).

After they are pollinated, the eucalypt flowers develop into woody fruits, known as capsules—that’s right, those gum ‘nuts’ we all collected as kids are technically fruits!

Eucalypt flower buds have little caps, called opercula, seen here in Eucalyptus synandra (Jingymia mallee). They help protect the flower bud from drying out and insect attack. Image adapted from: Tatters; CC BY-NC 2.0

Eucalypts have a notorious reputation for dropping branches, with many people considering them unsuitable for street trees or dangerous to have in their backyards. So, is this actually true? In times of drought or other stress, perhaps disease-induced, eucalypts will sometimes drop what looks to be a perfectly healthy branch with no apparent warning signs. During hot dry conditions, branches with insufficient water become brittle and can fall in windy conditions, especially from old trees. This can, understandably, instil a certain amount of apprehension in people. There are a few species in particular that are more prone to dropping their branches—manna gum (E. viminalis), river red gum (E. camaldulensis), yellow box (E. melliodora) and maiden’s blue gum (E. globulus).

Some species of gum tree are more likely to drop their branches than others. Image adapted from: Sydney Oats; CC BY 2.0

So if you’d like to plant one (or several) of these quintessentially Australian trees in your yard, but have safety concerns, first check the species. Make sure it’s appropriate for the size of your yard (there is a surprising number of smaller species) and plant it away from the house. Alternatively, enjoy gum trees by venturing out into the bush on the weekend and immersing yourself in the scents and atmosphere of the landscape.

Eucalyptus Tree Care – Tips On Growing Eucalyptus

Eucalyptus is a tree most often associated with its native Australia environment and fun-loving koalas feasting on its branches. There are many species of eucalyptus trees, including popular varieties like Gum tree and Silver-Dollar tree, that can be grown in the home landscape.

In fact, this tree can make an attractive addition with interesting bark and foliage, beautiful flowers, and nice fragrance. They do especially well in areas that mimic their native environment. Most of these trees are rapid growers, reaching heights of about 30 to 180 feet or more, depending on the variety, with approximately 60 percent of their growth established within the first 10 years.

Tips on Growing Eucalyptus Trees

All eucalyptus trees require full sun; however, some species, like E. neglecta and E. crenulata, will tolerate areas with semi-shade. They also adapt well to a wide range of soils, from hot, dry sites to slightly wet as long as the area is well draining.

Plant eucalyptus in mid to late spring or fall, depending on your location and climate. Be sure to water the tree both before and after planting. Dig the hole slightly larger than the root ball, and take care with the tree’s roots during planting, as they do not like being disturbed. There’s no need to spread out the roots while planting, as this could damage their sensitive root system. Back fill the area and lightly tamp the soil to remove any air pockets.

According to most eucalyptus tree information, many species respond well to potted environments as well. Ideal candidates for containers include:

  • E. coccifera
  • E. vernicosa
  • E. parviflora
  • E. archeri
  • E. nicholii
  • E. crenulata

Containers should be large enough to accommodate the tree, about 2 feet in diameter, and allow for adequate drainage.

Eucalyptus trees cannot take temperatures below 50 F. (10 C.) for extended periods; therefore, it’s recommended that they be grown indoors in cold climates, spending summers outside whenever warm enough. Other areas can either overwinter them indoors or provide suitable winter protection.

How to Care for a Eucalyptus Tree

Eucalyptus tree care is not difficult, as this type of tree usually maintains itself reasonably well. Once established, eucalyptus trees should not require too much watering, with exception for those growing in containers. Allow these to dry out somewhat between waterings. Additional watering may be necessary during periods of excessive drought, however.

As for fertilizer, much of the eucalyptus tree information recommends against the use of fertilizer, as they do not appreciate phosphorus. Potted eucalyptus may require an occasional slow-release fertilizer (low in phosphorus).

In addition, eucalyptus tree care includes annual pruning (in summer) to control top growth and their overall height. Eucalyptus trees are also known to produce heavy litter in the fall, shedding bark, leaves, and branches. As its shred-like bark is considered flammable, keeping this debris cleaned up is preferable. If desired, you can collect some seed once it falls, and then plant it in another area of your yard or in a container.

The Business of Growing Eucalyptus for Bioenergy

Three month old Eucalyptus tree seedlings will be prepared for shipment in the coming days.


Introduction to Florida Eucalyptus Varieties

One of the fastest growing trees in the world, the Eucalyptus, can grow to nearly 50 feet tall in four years. Each tree can be harvested four to five times during its 20-year life span.

The growing region for the Eucalyptus Grandis (energywood) include North Central and South Florida with the exception of the Florida panhandle area.

The Eucalyptus is planted from April through August. An ideal planting consists of between 1,000 to 2,000 acres, with adequate irrigation and fertilizer. All varieties of Florida Eucalyptus grow best on agricultural lands.

A non-invasive species, the Eucalyptus is a hardy and versatile tree, making it a low maintenance alternative crop for Florida farmers. Eucalyptus wood is used for a variety of products, including paper, lumber plywood, veneer, flooring, charcoal, firewood, fiberboard, essential oils, and landscape mulch. It also may be used for biofuel, with whole-tree chips supplying char and oil that can be transported and stored. The chips also can supply noncondensed volatile oil and low-energy gas to be used onsite or nearby.

Eucalyptus compounds can protect against insects, vertebrate herbivores, ultraviolet radiation, and cold stress. Among these are the terpenoids that give Eucalyptus foliage its distinctive smell.

At present three different Eucalyptus species are grown in Florida. E. grandis (EG) and E.amplifolia (EA) are fast-growing trees used for bioremediation applications, energywood and mulchwood. Corymbia torelliana (CT) are grown as windbreaks throughout southern and central Florida.


Eucalyptus is a hardwood widely planted throughout Africa, Asia, Australia, Europe, and North and South America. While the Eucalyptus is native to Australia, it grows in a variety of climates from the middle Carolinas south in the United States.

Eucalyptus trees were introduced in Southeastern United States in 1878 but not grown commercially in Florida until the late 1960s. Eucalyptus trees were introduced in Southeastern United States in 1878 but not grown commercially in Florida until the late 1960s. The Lykes Brothers of South Florida were widely credited with the first efforts to grow Eucalyptus trees for pulpwood production. In 1971 several other forestry companies provided essential support and acted as a driving force for commercialization of Florida’s Eucalyptus crop. During the 1980s three 100-year freezes nearly wiped out many Eucalyptus plantations in South Florida. Since that time new more cold-tolerant varieties have been developed and commercially grown throughout the Southeastern United States.

In the 1980s the University of Florida, US Department of Energy and The Gas Research Institute began conducting research on Eucalyptus for use in the bioenergy industry.

Why grow Eucalyptus Trees?

With increasing costs, growing concerns of carbon emissions, and increasing cost of fossil fuels Eucalyptus trees represent an enormous upside potential for growers in the bioenergy industry.

  • Eucalyptus trees produce feedstock for fiber and energy in short rotations
  • Increasing costs of fossil fuels make fuels and energy produced from biomass an attractive alternative source.
  • Eucalyptus trees offer a higher yield per acre and lower maintenance costs than other biomass crops such as miscanthus, switchgrass, hemp, corn, poplar,willow, sorghum, sugarcane, bamboo and other tree varieties.
  • Florida Eucalyptus varieties grow well on both marginal land and offer a lower maintenance alternative crop to citrus
  • Eucalyptus trees offer growers flexibility relative to other energy crops, both in terms of choice of when to harvest, and the multiple end use pathways including wood, fiber and energy.
  • Trees like Eucalyptus can be harvested year-round and provide a living inventory of available biomass, which reduces storage and inventory holding costs along with minimal shrinkage and degradation losses.
  • Because much of the infrastructure already exists, Eucalyptus trees will require fewer capital investments to harvest and transport, and costs can be spread throughout the year rather than concentrated in a short seasonal harvest period.
  • Harvesting trees will only happen every few years, reducing the environmental impact created by disturbances at harvest and planting.
  • While a comparable total acreage may be needed, with Eucalptus trees only a fraction of that total would be planted or harvested in any given year, compared to harvesting the same footprint each year for an annual crop.

Mulchwood Market and Applications

The color, texture and durability of Eucalyptus mulch offers an eco-friendly and more favorable alternative to cypress mulch. At present Florida mulch -manufacturing plants produce 20 million cubic feet of mulchwood each year. Based on typical growth rates of the Florida Eucalyptus varieties about 50,000 acres of Eucalyptus plantations would be required to meet market demands.

Pulpwood Market and Applications

Eucalyptus trees have been grown in South Florida for many years for use in the pulp and paper industry. The Florida-grown varieties have very acceptable properties for pulp and papermaking industries. Demand and prices for Florida Eucalyptus varieties remain strong thoughout the Southestern United States. Improvements in biomass conversion at pulpmills and biorefineries will drive the demand up for Eucalyptus in the coming years. Factoring in transportation costs, Eucalyptus plantations located within close proximity of pulpmills afford growers an opportunity to maximize the return on investment.

Bioenergy Markets and Applications

One of the fastest growing and most promising areas include production of Eucalyptus energywood for electricity generation. Woody biomass also has a number of other potential uses including direct combustion, thermo-chemical gasification, methane production and alcohol production. As an added benefit, trees grown for energy applications may qualify for tax credits. The number of wood pellet plants and biomass -fueled utility plants proposed or currently under construction could significantly increase demand for Eucalyptus.

Bioremediation Market Applications

The rapid year-round growth of Florida Eucalyptus varieties and makes it suitable for bioremediation applications such as effluent from sewage treatment plants, stormwater run-off in urban and industrial areas and agricultural irrigation water. Plantings as small as two acres could be commercially harvested in three to four years. Eucalyptus growers could potentially benefit from wastewater recycling, increasing tree growth, recycling nutrients while simultaneously producing mulch, pulpwood or energywood. Eucalyptus has proven to serve as an effective “bridge crop” to convert or restore lands infested with invasive species such as congongrass to agricultural uses.

History and Status of Eucalyptus Improvement in Florida


The first organized Eucalyptus research in Florida was begun by the Florida Forests Foundation in 1959 in southern Florida. This research was absorbed by the USDA Forest Service and the Florida Division of Forestry in 1968. In the early 1970s, the Eucalyptus Research Cooperative formed to provide additional support emphasized E. grandis, E. robusta, E. camaldulensis, and E. tereticornis and developed cultural practices for commercial plantations in southern Florida. In 1978, this cooperative united with the Hardwood Research Cooperative at North Carolina State University until 1985 when the 14-year effort ended after three severe freezes from 1983 to 1985. Eucalyptus planting and research were continued with a Florida-wide focus by the University of Florida and collaborators starting in 1980. The collective accomplishments in terms of genetic resources and commercial planting are summarized. For example, fast-growing, freeze-resilient E. grandis seedlings are produced by advanced generation seed orchards, five E. grandis cultivars are commercially available, as are E. amplifolia and Corymbia torelliana seeds. Genetic improvement of these and other species is ongoing due to beneficial collaborations. Short Rotation Woody Crop systems are promising for increasing productivity and extending uses beyond conventional pulpwood to applications such as windbreaks, dendroremediation, and energy wood.

1. Introduction

Eucalyptus species were introduced in the South as early as 1878, but no significant commercial plantations were established until the late 1960s . Although forestry organizations tested eucalypts in Florida in the 1950s and in Texas in the 1960s, most plantings before 1970 were small scale windbreaks, ornamentals, and shade trees in central and southern Florida and Texas.

In 1959, the Florida Forests Foundation initiated research on eucalypts as a potential source of hardwood pulpwood on rangeland or other low quality sites in southern Florida. The Foundation’s research was absorbed by the USDA Forest Service and the Florida Division of Forestry in 1968. In the early 1970s, a eucalyptus research cooperative was formed by seven companies to provide financial and research support to the Forest Service. This effort led to the selection of E. grandis, E. robusta, E. camaldulensis, and E. tereticornis from 67 species tested and to the development of cultural practices for raising seedlings and establishing commercial plantations in southern Florida .

In 1971, the Hardwood Research Cooperative at North Carolina State University (NCSU) began a systematic evaluation of species and sources to determine Eucalyptus suitability primarily for the Lower Coastal Plain of the South. By 1978, the industrial members of the Florida group joined the Hardwood Cooperative to pursue the Eucalyptus dream until 1985 when the 14-year effort ended as the result of severe freezes in December 1983, January 1984, and January 1985.

In Florida, Eucalyptus planting and research that started in south Florida in the 1960s were continued with a Florida-wide focus by the University of Florida and collaborators starting in 1980. The USDA Forest Service was a significant and active collaborator until its Lehigh Acres unit closed in 1984.

This paper reviews the history and status of tree improvement research activities with E. grandis, E. robusta, E. camaldulensis, E. tereticornis, E. amplifolia, and Corymbia torelliana in Florida. In the process, this paper first recognizes significant players in these activities and then highlights accomplishments in terms of genetic resources and commercial and potential uses. This paper also identifies continuing research needs.

2. Significant Players

Numerous institutions, companies, and individuals have contributed to the current status of eucalypts in Florida. The Florida Forests Foundation that initiated research in southern Florida benefitted from the efforts of George F. Meskimen, whose exceptional dedication to Eucalyptus research he jokingly once claimed came from being “seduced” by the genus’ attributes. The USDA Forest Service had a major role from 1968 to 1984, particularly through the activities of Thomas F. Geary and notably again George F. Meskimen. During this same time, the Florida Division of Forestry, with primary “on the ground” participation by Tim Pitman, facilitated eucalypt commercialization. Starting in the 1960s and continuing to the present, Lykes Bros., through the efforts of Charley Lykes, Ben Swendsen, and Jim Bryan, has been the major planter of eucalypts in Florida and a consistent supporter of related research. The six forestry companies in the Eucalyptus Research Cooperative (Buckeye Cellulose Corporation, Container Corporation of America, Hudson Pulp & Paper Corporation, International Paper Company, ITT Rayonier, and St. Regis Paper Company) provided essential support and impetus for commercialization starting in 1971 . These companies and other members of the Hardwood Research Cooperative at NCSU continued support of Eucalyptus research until 1985 . NCSU scientists who made significant contributions during this period included Carlyle Franklin and Bill Dvorak.

The Florida-wide Eucalyptus research conducted by the University of Florida (UF) since 1980 similarly has benefitted from many collaborators. The Short Rotation Woody Crops Program of the US Department of Energy funded research from 1980 to 1988. The Gas Research Institute provided support from 1981 to 1991. Other institutional supporters included the USDA Forest Service, the Florida Institute of Phosphate Research, Southeastern Regional Biomass Energy Program, USDA-SARE, Sumter County, and the Center for Biomass Energy Programs at UF. Buckeye Technology Florida, Mosaic, and Evans Properties are among the industries providing financial support, and many more contributed in kind through research collaboration, site preparation, and management. Among the numerous UF scientists involved in the research were J. B. Huffman, D. R. Dippon, H. Riekerk, G. R. Alker, D. R. Carter, L. Q. Ma, M. P. Ozores-Hampton, P. J. Minogue, J. T. DeValerio, K. V. Reddy, K. R. Roeder, E. I. Warrag, S. M. Pisano, B. Tamang, B. Becker, and M. H. Langholtz.

Collectively, the investments of personnel and resources in developing Eucalyptus for Florida are large. Scientist-years associated with the research conservatively exceed 100. Direct financial support to UF alone exceeded $3 million, and in-kind support over nearly 50 years may equal the direct funding.

3. Genetic Resources

A novel cost-efficient tree improvement strategy pioneered for E. grandis in Florida was followed for developing seedling seed orchards (SSOs) of all species . This inexpensive but effective strategy utilized eucalypts’ short generation time and rapid growth by combining provenance and progeny testing in one place at one time with early selection, large infusions of new, primarily single-tree accessions, and use of pedigrees to minimize inbreeding and achieve steady and often great genetic gains.

Five generations of E. grandis SSOs in southern Florida (Table 1) were started in 1961 by the Florida Forests Foundation using block plots of a limited number of accessions. The 1st-generation genetic base population of 4,352 trees from only 13 accessions was quickly thinned to an SSO of just eight trees from three accessions, which in turn were carried forward into the 2nd-generation genetic base population planted in 1964. While this population had 11,000 trees from 18 accessions, the resulting SSO had only 33 trees from 12 accessions.

Generation Year Base population Orchard
Trees Accessions Trees Accessions
E. grandis seedling seed orchards
1 1961 4,352 13 8 3
2 1964 11,000 18 33 12
3 1973 13,234 285 431 191
4 1977 31,725 529 1,500 260
5 2002 1,620 69 73 33
5 2010-11 1,300 26 ~260 ~20
5 2011-12 5,580 36 ~480 ~25
E. grandis clonal seed orchards
4C 1996 154 41
4C 2007 176 36
E. robusta seedling seed orchards
1 1961 2,304 9 119 ??
2 1967 6,275 64 94 39
3 1975 24,476 372 706 191
E. camaldulensis/E. tereticornis seedling seed orchards
1 19?? ? ?? ?? ??
2 1974 13,421 184 243 150
E. amplifolia seedling seed orchards
1 1992 1,685 109 139 106
2 1999 1,638 59 40 22
2 2003 216 22 33 12
C. torelliana seedling seed orchard
1 2008 960 29 69 25

Table 1 Numbers of trees and accessions in Florida Eucalyptus grandis, E. robusta, E. camaldulensis/E. tereticornis, E. amplifolia, and Corymbia torelliana genetic base populations and derived seedling or clonal (C) seed orchards by generation and year of establishment.

To expand this narrow genetic base, the 3rd- and 4th-generation genetic base populations received major infusions of new accessions, primarily individual tree seedlots. When planted in 1973, over 13,000 trees from 285 accessions were deployed as single-tree plots in a completely randomized design. Based on 1.5-year tree size data, the 3rd-generation SSO (GO73) was then created with 431 trees of 191 accessions unequally distributed across the SSO (Figure 1).

(b) Figure 1
Aerial views of GO73 (front) and GP77 (back) in 1980 (a) and GO73 and GO77 in 1993 (b).

The 4th-generation genetic base population (GP77) established nearby in 1977 with a worldwide representation of E. grandis of over 31,000 trees from 529 accessions was again completely randomized in single-tree plots across more than 12 ha (Figure 1) . At 1.5 years, nearly half of the trees were felled to evaluate wood properties and coppicing. From the resulting data, area selects (the best tree in 4 rows of 5 trees) were made to constitute the 4th-generation SSO (GO77) (Figure 1). The final GO77 composition created in 1985 also utilized individual tree responses to severe freezes from 1983 to 1985. These 1,500 orchard trees have produced seed for many commercial plantings in Florida and elsewhere.

The effectiveness of this tree improvement strategy was evident in comparisons across generations in GP77 for tree volume (Figure 2). The comparison of 1st-generation E. grandis with E. saligna supported dropping E. saligna from the research program. A near doubling of tree size in 2nd-generation E. grandis demonstrated the payoff in selecting for adaptability to the infertile soils and seasonal rainfall of southern Florida. The 16% gains in tree volume in successive generations illustrate the benefit of continued selection and orchard establishment.

Figure 2

Including the genetic base populations that served as large open-pollinated progeny tests, some 25 smaller progeny tests of E. grandis in GO73 and GO77 were planted in southern Florida since the 1970s . GP77 and eight of these smaller tests with appropriate tree size and freeze responses, in combination with the multigeneration pedigrees that have been maintained, have recently contributed to the calculation of breeding values for 2,174 trees for stand basal area and/or freeze resilience (the ability to reestablish vigorous vertical growth after freeze damage).

The severe freezes of the 1980s afforded exceptional opportunities to develop fast growing, freeze resilient clones (Table 2), and several clone banks were established. Most of the early emphasis was on E. grandis, with genetic tests distributed widely across sites and climates in Florida. Based on the resulting performance (Table 3), UF has patented and released five cultivars: E.nergy series E. grandis cultivars G1, G2, G3, G4, G5 , which grow well under many circumstances (Figure 3).

Species Selected Tested Commercialized
E. grandis 390 350 5
E. robusta 52 52 0
E. camaldulensis/tereticornis 28 4 4
E. amplifolia 115 35 0
C. torelliana 4 0 0

Table 2 Numbers of clones selected, tested, and commercialized by species.

Characteristic Cultivar
G1 G2 G3 G4 G5
Growth Fast Fast Fast Fast Fast
Freeze resilience Average Good Excellent Excellent Average
Wind firmness Suscept. Average Average Resistant
Coppice Good Good Good Good Good
Tissue culture propagation Readily Readily Readily Good Good
Pedigree (gen.) 4th 4th 2nd 2nd 3rd
Wood density (kg/m3) 522 470 640
Wood moisture content (%, dry wt) 119 104–123 128-129 89
Chalcid resistant No Yes Yes Yes Yes
Plant in south FL Yes Yes Yes Yes Yes
Plant in central FL No Yes Yes Yes Yes
Plant in north FL No Yes Yes Yes No

Table 3 Characteristics of E. nergy series E. grandis cultivars G1, G2, G3, G4, and G5.
(b) Figure 3
13.3-year-old G4 on dredge spoils (a) and 2-year-old G1, G2, G3 on phosphate mined land (b) in central Florida.

Progeny test results, breeding values, convenience, and/or security of multiple orchard locations led to the establishment of additional E. grandis orchards (Table 1). Small clonal seed orchards were established in 1996 and 2007 to be closer to facilities and to protect against tree loss due to storms, respectively. For similar reasons, 5th-generation seedling seed orchards have also been developed using multiple-tree row plots in randomized complete block designs.

In the early species comparisons in southern Florida, E. robusta appeared to be comparable to E. grandis, and hybrids between the two species were promising . Therefore, similar emphasis was given to E. robusta seedling seed orchards (Table 1). In 1975, the 3rd-generation orchard RO75 was established using comparable techniques to GO77 , but after RO75 was rogued, the top E. grandis progenies were interplanted to encourage production of spontaneous hybrids. Following this unproductive effort, RO75 was harvested and is no longer viable.

Some E. robusta candidates were selected and clonally tested in the early 1980s (Table 2). However, the E. robusta clones failed to perform well, and none were ever commercialized.

Early species comparisons also showed promise for E. camaldulensis and E. tereticornis, resulting in a 1st-generation seedling seed orchard (Table 1). A considerable effort in 1974 expanded the genetic base population for these species, and seedling seed orchard CT74 was eventually developed.

Because seed production was problematic, some E. camaldulensis and E. tereticornis clones were selected (Table 2). A few of these were commercially propagated for use in California in the 1990s but are no longer available.

Reevaluation of a number of species resulted in expanded tree improvement efforts with two species that had been considered of limited potential. For both E. amplifolia and C. torelliana (formerly E. torelliana), the starting germplasm was derived from seed or trees resulting from earlier screening efforts. The Florida Division of Forestry had retained and grown small quantities of E. amplifolia and C. torelliana because of their ornamental properties.

Two generations of E. amplifolia orchards have been established (Table 1) for producing seed for planting in more freeze-frequent northern Florida and similar areas. The 1st-generation genetic base population included many new accessions, particularly individual tree accessions from frost-frequent portions of the species’ natural distribution. Most of those accessions were retained in the SSO AO92. The two 2nd-generation orchards (Figure 4) included seedlings from AO92 but were mostly composed of additional new accessions. Commercial seed is available from two of the SSOs, and breeding values will be calculated from all 15 progeny tests that have been established since 1998.

(b) Figure 4
E. amplifolia seedling seed orchards at 8 years (a) and five years (b).

Collectively, over 100 E. amplifolia cloning candidates have been identified, with some 35 entered in tests. Since rooting percent in E. amplifolia is highly variable but typically half that of E. grandis (40% versus 80% ), many more candidates may be needed before commercialization.

The C. torelliana genetic base population planted in 2008 (Table 1) included seedlots from 29 trees in windbreaks established from Division of Forestry and retained seed of unknown source. Surprisingly, this tropical species has demonstrated tolerance to temperatures as low −5°C, and all 69 orchard trees combine freeze tolerance with good growth and tree form (Figure 5). New Australian accessions have been acquired for inclusion in the 2nd-generation base population.

(b) Figure 5
3.4-year-old C. torelliana orchard (a) and a tree in the orchard (b).

A few C. torelliana cloning candidates have been identified (Table 2). Capture has been by tissue culture, with no trees yet ready for field testing.

Other eucalypts are currently being tested for Florida conditions. One company is testing E. benthamii, E. macarthurii, and a genetically engineered hybrid of E. grandis × E. urophylla with genes for cold tolerance, lignin biosynthesis, and/or fertility . Using more recent and broader germplasm than what was represented in earlier tests, NCSU and several collaborators started in 2010 assessing 149 species at 11 locations in the Southeast, including two in Florida, with about 30 species per location .

4. Uses

Matching Eucalyptus species to Florida’s diverse weather and soils is challenging. Historically defined climatic regions based on average low temperatures or numbers of freezes provide some broad guidelines, but annual aberrations such as the three 100-year freezes in the 1980s , extended cold periods of the 2010-11 winter, and the abrupt freezes of the “warm” winter of 2011-12 profoundly influence freeze susceptibility of all young eucalypts. Rainfall patterns with unpredictable, extended dry spells make Florida’s summer rainfall climate highly variable and difficult for successful planting and early growth. Within climatic regions, soils available for planting eucalypts can range from sandy, infertile to heavy clay to limestone to organic.

Still, broad climatic regions provide initial guidelines for using the species (Figure 6). From southern into central Florida, C. torelliana will tolerate typical winter conditions and grow well across a range of sites, especially when irrigated on deep sands. In peninsular Florida, E. grandis, especially hardier cultivars (Table 3), will tolerate most winters and sites even into northeast Florida. While typically tolerant of the colder winters common to northern Florida and similar regions, E. amplifolia requires good fertility with unless appropriate amendments are added to the infertile, poorly drained soils common to much of the region.

(c) Figure 6
Planting regions in Florida for C. torelliana (a), E. grandis (b), and E. amplifolia (c).

Eucalyptus planting is still largely done in southern Florida. One large landowner maintains a plantation estate of ~8,000 ha of primarily E. grandis in southern Florida. Two commercial plantations of ~32 ha of E. amplifolia have been established in northern Florida. No traditional plantations of C. torelliana have yet been established, but it is widely used for windbreaks in central and southern Florida.

Market opportunities for Florida eucalypts are currently limited but have huge potential. The hardwood pulpwood market forecast for southern Florida grown eucalypts in the 1970s that was made uneconomical by high transportation costs instead became a more local mulch wood market (Figure 7) that supplies Eucalyptus mulch widely across the US. As cypress availability decreases, more eucalypt wood may replace it. In areas close to existing pulp mills in northern Florida, specialty pulps may utilize eucalypts.

(d) Figure 7
Uses of E. grandis in Florida—mulch wood (a), energy wood (b), dendroremediation (c), and windbreaks (d).

Other traditional wood markets for eucalypts elsewhere are undeveloped or untapped in Florida. For solid wood products such as lumber and flooring, E. grandis grown in longer rotations would be suitable. As medium density fiberboard, E. grandis and/or E. amplifolia are suitable, as well as for wood-cement boards, plywood, and oriented strand board .

Eucalyptus energy wood uses in Florida have been demonstrated and are planned . For cofiring in compatible coal-fired power plants, E. grandis is a suitable feedstock. Eucalyptus is being considered as the feedstock for energy generation at pulp mills in Florida. It has potential for use in biorefineries even in association with pulp mills . For several stand-alone biomass power plants in the state, Eucalyptus is proposed as the primary feedstock .

Short Rotation Woody Crop (SRWC) systems can maximize eucalypt productivity for such uses . Due to their easy propagation, rapid growth, tolerance to high stand density, response to intensive culture, and coppicing, E. grandis (Figure 7) and E. amplifolia in SRWCs can produce up to 67 green mt ha−1 yr−1 in multiple rotations as short as three years in Florida. These species are very responsive to intensive culture options such as soil amendments, vegetation control, and irrigation.

Eucalyptus grandis, E. amplifolia, and C. torelliana also have other uses in Florida. While each can be used in windbreaks , E. grandis (Figure 7) and especially C. torelliana have been widely planted around citrus groves and vegetable fields in central and southern Florida. For dendroremediation (tree uptake of nutrients, reclaimed water, contaminants, etc.), E. grandis (Figure 7) and E. amplifolia can be very effective . Eucalypts can serve as “bridge crops” to convert lands infested with invasive species such as cogon grass (Imperata cylindrica) to agricultural uses .

5. Research Needs

While genetic and silvicultural improvements to date primarily with E. grandis, E. amplifolia, and C. torelliana have dramatically improved Eucalyptus productivity in Florida, considerable progress remains to be made through research in several areas. Within the genus, more recently tested species, such as E. benthamii, may demonstrate suitability for Florida’s demanding climatic and site conditions.

Within the species suitable for Florida, progress is needed in freeze resilience, growth rate, coppicing, pest resistance (e.g., the blue gum chalcid ), and propagation. Advanced generation breeding in combination with seedling and clonal seed orchards can continue making gains in these traits, but dramatic improvements are possible with clonal selection and testing. For example, interspecific hybridization and genetic modification, using gene mapping and genomic selection, could produce cloning candidates .

With the advent of proven clones, economical and rapid propagation becomes a need. Current vegetative propagules are ~33% more expensive than seedlings. Florida’s seasonal planting schedule further necessitates the need for periodic rapid buildups of propagules.

Silvicultural enhancements are needed. Because of the infertility, low pH, and low organic matter of many sites available for planting eucalypts in Florida, appropriate organic fertilizers and water absorbing gels need study. Environmentally friendly applications of inorganic fertilizers need documentation. Weed control treatments are not well developed for eucalypts in Florida. Application of available wastewaters to plantations needs to be commercialized. Growth and yield models reflecting genetic and silvicultural improvements will be needed.

Market expansion for eucalypts in Florida depends on energy project development and technology improvement. The current market for eucalypt mulch wood is met by existing plantations, but the mulch wood market could expand if cypress availability decreases. The number of wood pellet plants and biomass-fueled utility plants currently under construction and proposed for Florida could significantly increase the demand for eucalypts. Improvements in biomass conversion at pulp mills and stand-alone biorefineries would also increase demand.

6. Conclusions

Fifty years of concerted effort by many players have developed eucalypts of typically satisfactory growth, freeze resilience, and site tolerance in most of peninsular Florida. In southern and into central Florida, E. grandis seedlings from advanced generation orchards may be successfully deployed in most years. Five E. grandis cultivars (E. nergy G1, G2, G3, G4, G5), resulting from freeze resilience screening afforded by extreme winters, may extend the E. grandis planting zone into northeast Florida. For southern and central Florida, C. torelliana seed is now available from a 1st-generation seedling seed orchard. For northern and into central Florida, improved E. amplifolia seed is available.

These species may be used for multiple products. Mulch wood is the current market for E. grandis and E. amplifolia, while E. grandis and particularly C. torelliana are used for windbreaks. Using SRWC systems, the productivities of these species are high and will be required to meet feedstock demands when energy wood markets develop.

Genetic improvement is ongoing to increase growth and particularly to address freeze resilience and pest resistance needs. Collaboration will be beneficial for continued progress in realizing the attributes of Eucalyptus under Florida conditions.


Thanks are due to the National Council for Air and Stream Improvement, Inc. and the USDA Forest Service Southern Research Station for their invitation and support in attending and presenting at the Symposium on the Assessment and Management of Environmental Issues Related to Eucalyptus Culture in the Southern United States in Charleston, SC, from February 22–24, 2012. This paper is based on that presentation.

Not just a border tree — possibilities with eucalyptus crops

IF THERE’S ONE THING local citrus growers are paying close attention to of late, it’s the concept of alternative crops. As citrus greening continues to threaten citrus crops and cause hardships for growers, researchers, business leaders, and farmers have devoted sharp attention to what other products they can grow besides citrus.

One product that’s causing a stir and attracting attention is the eucalyptus tree. Many may hear “eucalyptus” and think of Australia and koala bears. But here in Florida, the term is beginning to bring much to mind: the product can be used as an energy source, as mulch, and more. It’s been used as windbreaks to protect crops from wind damage, chemical drive, and airborne disease, but the current line of thinking is toward other advantages than protection of citrus trees.

Leading eucalyptus expert Dr. Don Rockwood says the fast-growing trees that have been developed for this state’s climate are tolerant to cold weather and do not need much maintenance — a big plus for growers of citrus, peach, and other crops that need a lot of attention.

Dr. Rockwood has spent decades studying the trees and has patented several varieties. They are ideal for Florida’s former citrus beds, he points out. “There’s just a kind of residue there that makes those lands more attractive than palmetto prairie kinds of soils, for example.”

“And eucalyptus has an established market for mulchwood throughout the eastern United States,” he adds. “Yet, there is the very real prospect of using fast-growing trees as an alternative energy.” Local grower Phillip Rucks says he is in agreement that eucalyptus has potential. Rucks planted 13,000 of the trees in Georgia several years ago, and a serious freeze killed all but 1,000 of them. While that might seem like bad news to many, Rucks was encouraged by the fact that 1,000 lived through a Georgia freeze — they are likely to survive Florida’s cold snaps. Dr. Rockwood confirms that varieties developed for Florida will indeed survive the chilliest temperatures. He has many patents on varieties of eucalyptus. “The cultivars were selected and bred to withstand our freezes,” he states.

And there are more pluses for the eucalyptus option. The trees take three to six years to reach harvest size, giving growers a much faster return on their investment. “When everything goes right, these trees can grow 15 to 20 feet a year,” he explains. “That is three to five times the rate of pine trees. And fast-growing trees can be harvested three times before they need replanting.”

It takes time to change the agricultural landscape, however. “In terms of using trees for variation crops, one issue is that there are changes necessary — and landowners are slow to change from whatever they have been doing to something else,” Dr. Rockwood says. “Another factor is that ag land prices are high now, and in order to make it a profitable venture, there needs to be several hundred acres.”

Grower Rucks supports the changes; they are needed to keep growers afloat. “We just have to work through it,” Rucks says. “Continue trying to keep an open mind, and look at something that’s going to fit in our climate.”

To attract businesses interested in turning the trees into an energy source, thousands of acres need to be in the ground, according to Dr. Rockwood. “With wood resources, there needs to be hundreds of thousands of tons of wood,” he says. “To attract a power plant, there needs to be quantity.” And local growers can’t produce the crops to do business with power plants located further away. “They need to be 50 to 60 miles from the plant,” he observes. Transportation costs would otherwise be too much.

Besides being a source of multiple uses, eucalyptus trees equal jobs. “For a community,” he concludes, “it would provide quite an economic boon.”


article by MARY TOOTHMAN

Tags: agriculture, alternative crops, citrus, citrus greening, citrus growers, cultivar, Dr. Don Rockwood, Eucalyptus, mulch, mulchwood, peach, power plant, renewable energy, windbreaks

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