Red Gum (not native)

                          “…no tree is more beautiful in the wind or against the sky, and none provides better nesting
for the soft-voiced mourning dove…”
Lawrence Clark Powell (speaking at Mills College, 1956)

                          “I can’t be expected to produce deathless prose in an atmosphere of gloom and eucalyptus.”
Gerald Durrell, (My Family and Other Animals, 1956)

Few plants are as controversial as a Eucalyptus. It has been called “miracle tree” and “noxious weed.” Red gum (Eucalyptus camaldulensis) is one of many species of eucalyptus, or eucalypts, that were introduced into California for wood, shelter, landscaping and for their presumed curative powers. It is one of a few species have escaped into natural areas where they displace native species and create a fire hazard. In San Elijo they are in conflict with our goals as an an ecological reserve and are unwelcome.

Over the years, red gums in the Reserve have grown and fallen and reseeded. They are invading our elfin forest on the southwest and our marsh on the north. Last month (October 2017) a program was initiated to remove these red gums and replace them with oaks, and riparian trees such as cottonwoods, sycamores and willows. The immediate effect is not pretty, but restoration plans are well underway and in a few years we will have a healthy and diverse association of native riparian plants blending natural marsh and upland oaks.

Description ^4,41,199

Red gums are large evergreen trees, with deep roots and a full crown of leaves; it may grow to 100-150 feet (30-45 m) in height. Trunks are usually straight. The wood is dark red, giving this species its name. The bark sheds in long strips leaving a smooth, mottled trunk of white, tan and gray. Long, slender twigs are reddish and droop downward with blue/olive, leathery leaves that are lanceolate or sickle-shaped, two to eight inches (5-20 cm) long and less than two inches (5.5 cm) wide with smooth margins.  Numerous tiny glands are embedded between the veins of each leaf; these produce the volatile oils that give the red gum its distinctive aroma. Unlike the young leaves of many eucalypts, juvenile leaves are not markedly different from adult leaves.

Red gum flowers occur in small umbels of creamy white flowers from leaf axils of young shoots. The structures of eucalypt flowers and fruit are unique; Johnston gives an excellent photographic description of one species.¹⁹⁷ In red gum, the base of the flower, the hypanthium, is a bowl-like structure, which encloses the developing pistil and stamens. Traditional petals and sepals are absent. Instead, these have united into a bud cap that covers the end of the hypanthium, protecting the immature pistil and stamens. In red gum, the bud cap is conical with a long, projection. Just prior to flowering, the stamens expand and push off the bud cap. The “flower” of a red gum is a spray of numerous white stamens, nestled within which is a stout, green pistil; the pistil becomes receptive after the stamens have shed their pollen, minimizing self-fertilization. The main flowering time of red gum is in spring,⁷ but we have found flowers in mid-summer.

The fruit of a eucalypt is often called a gumnut. Each gumnut is a compound structure of hypanthium and ovary, which becomes woody when mature. In red gum, the fruit is generally less than 1/2 inch in diameter. The rounded top of the ovary projects from the center, and tiny angular seeds are released through four triangular valves in the top.

Classification ^2,44

Red gum is a dicot angiosperm in the myrtle family (Myrtaceae). The myrtle family contains as many as 3000 species in 130-150 genera, mainly in the Southern Hemisphere. All species are woody and have floral parts in fours or fives. They range throughout the world’s tropical and subtropical regions and make up a large part of the tree and shrub population of Australia. The evergreen leaves are simple and mostly opposite with entire margins. Juvenile leaves are often distinct from mature leaves. Most species have numerous brightly colored stamens, leaves with strongly-scented oils, and fruits that are either capsules or fleshy berries. Some of the more well-known members of the family are the species of Eucalyptus and of bottle-brush (Callistemon), as well as guava (Psidium guajava), allspice (Pimenta dioica), and cloves (Syzygium aromaticum).

There are more than 700 species within the Eucalyptus genus and most, if not all of them evolved in Australia;¹⁹⁶  The taxonomy is complex and not completely agreed upon. Red gum is distinguished from the other ten species of Eucalyptus in California wildlands by the nature of the bark, the structure of the flower cluster and the size and structure of the gumnut.²

At present (2017) there are several subspecies and varieties of red gum accepted in Australia.^41,202 These are not recognized in California.^2,7

Ecology  

For many people, a shady grove of eucalypts on a warm afternoon has a quiet, dreamy appeal. A soft haze perfumes the air with clean, sharp smells. These aromatic air-born compounds are thought to be part of the survival strategy of eucalypts – and they are a large part of the controversy surrounding them. Eucalyptus oils may have adaptive values for eucalypts but negative effects on our native species.

Eucalyptus oils are reported to be “allelopathic”, leaching into the soil and suppressing the germination and growth of nearby plants that might compete for water, nutrients or light.³⁶² This, however, is a very complicated subject and not all agree that allelopathy exists as often as claimed.^363,364 The same oils also retard the breakdown of Eucalyptus litter, possibly because the growth of decay organisms is inhibited, and the accumulated mass of bark, sticks, and leaves also restricts the growth of their understory. Thus, whether the action is direct or indirect, eucalyptus oils act to impede the growth of the understory and reduce the diversity of plants in a eucalyptus grove.^202,362

Eucalypt oils are also highly flammable, exploding during a fire which is further fueled by the accumulation of litter beneath the trees.^41,367 Many eucalypts have developed a unique method of fire survival. Whereas most fire-adapted trees send up new growth from the tree roots, eucalypts have specialized buds deep within their bark which have high fire survivability and allow rapid post-fire recovery from the trunk and branches.³⁶⁴ Eucalypt gumnuts are opened by fire, releasing the tiny seeds that thrive in a post-fire soil.³⁶⁷ There is even a theory (not always accepted) that the high oil content of eucalypts, up to 20% of the dry weight, is not merely an adaptation to suppress the growth of competitors around a tree, but an adaptation to promote fire, effectively removing competing species from the forest.³⁶⁴

Human Uses ^41,365,366

In Australia, the aborigines used species of Eucalyptus for a variety of medicinal and construction purposes; red gum bark was especially important for their canoes. They also developed a method for obtaining fresh water from the red gum roots.

In modern times, red gum is reported to be the most popular plantation-grown tree and is often grown for firewood, charcoal, and biofuel as well as for pulpwood. The attractive red colors of the wood make red gum a desirable wood for many craftsmen, but, because of the tendency of young red gum wood to twist and crack, it must be carefully selected, seasoned and worked for more visual products such as sculptures and furniture.

Australia has always produced high-quality lumber from Eucalyptus species. The best whalers in the Southern Ocean were reputed to be those made from Eucalyptus wood. This high-quality lumber, however, comes from old-growth forests, from trees hundreds of years old, and the quality of this wood is much different than that of the young, plantation-grown trees most commonly used in other countries.³⁶⁶

Interesting Facts ^41,231,366

“San Diegans planted olives by the hundreds, citrus by the thousands and eucalyptus by the multi-millions.” ²³¹

At the start of the 20th Century, the railroads were rapidly expanding, and their need for wood grew dramatically. In 1906, the Atchison Topeka and Santa Fe railroad purchased the 8600 acres Rancho San Dieguito, north of San Diego and five miles from the coast. They planted three million eucalypts, mostly red gum, with the intent of harvesting them as soon as the trees matured – after about 15 years. It did not take long to learn that their gum trees were more like “bubblegum trees”;²³¹ that they twisted and cracked when drying and would not hold a railroad spike. The project was abandoned, and the red gums flourished!

Following World War II, the Santa Fe railroad sold Rancho San Dieguito to developers who nestled homes in the red gum groves, gave the area a Spanish feel and changed the name to Rancho Santa Fe.  It is now one of the most sought-after addresses in the world and the red gum is its icon.

A few red gums, however, were planted within what is now San Elijo Ecological Reserve. They too have flourished, occupying land that would naturally be claimed by native riparian trees such as sycamores, cottonwoods, and willows.  These red gums are in direct conflict with Reserve goals of restoring and maintaining native vegetation.

In October 2017,  red gums were removed from half an acre at the western edge of the grove. The first replanting is expected to occur in December with the planting of more than 1400 native species. Eventually, the Reserve will once again have a shady, green and diverse canopy over the La Orilla trail.