The University of Tennessee - Forest Resources Research and Education Center

Two large, impressive trees in the Arboretum’s Conifer Collection are the Japanese Cedars on the hill above the Program Shelter. These are not true cedars, but belong to the Cupressaceae family, which also includes junipers, bald cypress, arborvitae, and redwoods. A dwarf form of this tree can be found in the Dwarf Conifer Collection. This ancient tree is the National tree of Japan and is also called "Temple Tree" for its use in building the centuries-old Shinto temples. It has a pyramidal, conical shape with somewhat pendulous branches. It is evergreen, grows 50-60 ft high (though old trees as high as 230 ft have been reported).

Japanese Cedar has blue-green, needle-like leaves and a red-brown bark that peels off in vertical strips. The seed cones are globular. It is a forest tree native to Japan (16% of Japanese managed forests are of Japanese Cedar). It has a wide variety of uses in construction and the manufacture of furniture, utensils, and paper. It is cultivated as an ornamental, landscape tree, and is frequently used for Bonsai.

Sweetgum (Liquidambar styraciflua)

Sweetgum is a deciduous tree that holds onto its leaves late into the fall. In December one can still find occasional trees with a few yellow to purple leaves along with conspicuous stalked, spiny fruits hanging from the branches. At the Arboretum, Sweetgum is most commonly found along the Old Kerr Hollow Road in a relatively moist habitat.

Sweetgum is found in much of the Eastern U.S. south of New England. The fruits consist of seed pods united into dense spiny balls. The bark is deeply furrowed into narrow ridges, and the twigs often develop corky ridges along their length. The lobed leaves, which resemble maple, have a pungent odor when crushed. The gum from which Sweetgum derives its common name has been used since before the 16th century for incense, perfumery and medicinal purposes. Sweetgum lumber has a variety of uses such as furniture, crates, cabinets, and barrels, and its distinctive heartwood is often referred to as "red gum" lumber. It is also an important shade tree.

Japanese Umbrella Pine (Sciadoitys verticella)

Mid to Late December

One of the more interesting trees in the Arboretum’s Dwarf Conifer Collection is the Japanese Umbrella Pine. The common name of this tree comes from the long green, needle-like "leaves" that occur in whorls resembling the spokes of an umbrella. These photosynthetic "leaves" have been interpreted as actually being stem tissue rather than leaf tissue and are referred to as cladodes. They persist for 3 years. The true leaves are small brown, scale-like structures that are found along the shoot between the whorls of green cladodes and are also tightly clustered around the bases of the cladodes.

The slow-growing Japanese Umbrella Pine can reach a height of 20-30 feet. Its reddish-brown bark peels off in strips. In its native Japan, this species grows in cool, moist, mountainous environments. The wood is used in Japan for building boats. Several cultivars have been developed as unusual landscape trees. As the sole member of the plant family Sciadopityaceae, the Japanese Umbrella Pine is known from the fossil record as far back as 230 million years.

Northern Red Oak (Quercus rubra)

Northern Red Oak, a fairly common tree in our deciduous forests, is found along many of the Arboretum trails. As the common name implies, it is most prevalent in northern hardwood forests, but is found throughout Tennessee. Its range extends from the Maritime Provinces and eastern Canada south to Alabama and Georgia, and west to Minnesota, Nebraska and Oklahoma. The lobes of the alternate, dark green leaves are bristle-tipped, a characteristic of other members of the red oak group, and turn brick red in the fall. In poor years, however, the leaves are likely to be red-brown to yellow. The acorns are up to 1 in. long and have a cap covering up to 1/4 of the nut. The bark is lightly to deeply furrowed, frequently with light-colored plates running up and down the trunks between the fissures. The acorns are prime food for squirrels, turkeys, deer, black bears, and other wildlife. Although Northern Red Oak frequently produces large crops of acorns, squirrels and other wildlife may consume 80 to 100% of the acorns in any given year. Northern Red Oak is an important lumber tree, with a wide variety of uses in construction and furniture making.

Christmas Fern
(Polystichum acrosticoides)

A walk along the Arboretum trails during winter months finds very few green plants on the forest floor. The evergreen leaves (fronds) of Christmas Fern, however, persist throughout the winter months. New growth is initiated in early April when young leaves, known as fiddleheads, emerge. Although the fiddleheads of other ferns are considered delicacies, the scaly nature of the leaf rachises of Christmas Fern detract from their culinary appeal.

In late May and early June, clusters of brown sori (spore-bearing structures) are found on the underside of the upper 1/3 of the fertile fronds (leaves). Christmas fern gets its common name from its stocking-shaped leaflets along the pinnately compound leaves and from the historical use of the leaves as Christmas decorations. The species is widely distributed in forests of the Central and Eastern U.S. It is frequently planted for groundcover, especially in shady areas and on slopes. Because it is evergreen and has a well-developed underground rhizome system, it is used in landscaping to help control erosion.

Mistletoe (Phoradendron leucarpum)

Clumps of Mistletoe resembling large green squirrel nests become conspicuous in the upper branches of deciduous trees after the leaves have fallen. Sprigs of its green leathery leaves and stems and its white berries are a familiar component of the Christmas time tradition of kissing under the Mistletoe. In ancient times it was used by Druid and pre-Christian traditions to decorate houses at the mid-winter and mid-summer solstices. In our area, Mistletoe is found on such trees as oaks, hickories, red maples, and sweetgums.

Although not commonly found at the Arboretum, Mistletoe is frequently seen in Oak Ridge, Clinton, and along the Pellissippi Parkway. It is considered to be semi-parasitic because its modified roots penetrate the bark and vascular tissues of the host tree and access water and minerals for the developing plant, but it does not appear to harm the host. In the winter, Mistletoe clumps consist of a heavily branched system of greenish stems bearing opposite, leathery, leaves containing chlorophyll. While these clumps are heavily shaded by the host tree’s canopy during the summer, they are well adapted to photosynthesize after leaf fall - it has even been suggested that they may contribute food to the host tree during the winter months.

Mistletoe bears inconspicuous yellow flowers and white, translucent berries. Birds disperse the seeds in their droppings and by wiping sticky residues of the fruits adhering to their beaks onto other trees. Phoradendron leucarpum occurs throughout much of the eastern US from New Jersey to Florida and as far west as Texas and Illinois. Species of Mistletoe in the western US are parasitic on conifers and can be a significant problem.

Ground Pine (Lycopodium obscurum)

Ground Pine (also known as Rare Clubmoss or to locals as “Piney”) is a non-flowering vascular plant. Although present on Arboretum property, it is not commonly seen along our public-access trails. Its resemblance to a small pine tree is the basis for its common name. It has simple leaves (microphylls) with a single, unbranched vein running their length. A cone-like structure (a strobilus) is borne at the tip of a vertical branch. The strobilus consists of modified leaves which bear sporangia in their axils. The spores produced develop into small, separately growing haploid plants (gametophytes) that eventually produce eggs and sperm. Once fertilization occurs, a new diploid sporophyte develops. Ground Pine spreads vegetatively by producing horizontal runners that grow below the ground surface. Over time, an extensive colony of interconnected plants can develop. Ground Pine is one of several genera of vascular plants related to ancient tree-sized plants (e.g., Sigillaria and Lepidodendron) that were major components in the formation of coal beds.

Oriental Bittersweet (Celastrus orbiculatus)

A walk along Cemetery Ridge Trail during our first snowstorm of the year (December 5, 2009) highlighted the bright red fruits of the Oriental Bittersweet vines that climb and, in some cases, cover some of the trees and shrubs along the trail. The fruits are initially green, but become bright yellow at maturity. When the yellow capsule breaks open in the fall, it reveals a fleshy red aril which contains two brown seeds.

The small greenish flowers develop in the spring (at the end of April this year). Each flower is typically unisexual — either male or female, but some perfect flowers occasionally develop. The leaves are rounded to acute/elliptic, the latter shape being more common at the end of young developing shoots.

This invasive woody vine was introduced to the US in the mid- to late 1800s and is especially troublesome in New England, the Atlantic coastal states, and the southern Appalachians. The vine aggressively twines around tree and shrub stems and can strangle (by girdling) or completely covers and shades out its hosts. The fruits are eaten and spread by birds. People also inadvertently help spread the attractive fruits which they gather for holiday decorations. Such decorations should be destroyed completely after the holidays to limit the spread of this invasive plant. At the Arboretum, Oriental Bittersweet is most common in relatively open areas along forest edges and is one of several invasive plants the Arboretum staff is attempting to eradicate.

Shortleaf Pine (Pinus echinata)

The area currently occupied by the Arboretum was mainly farmland when the government took it over in the early 1940s. Shortleaf Pine and Virginia Pine (P. virginiana) were two of the trees that first invaded the abandoned farmlands. These pines grow in the open, where competition from other trees for light, moisture, and nutrients is limited. As the forest developed, deciduous species such as oaks, hickories, and tulip poplar, gradually became established and have become the dominant trees. Recent research at the UT Forest Resources Center in Oak Ridge and the Chuck Swan State Forest near Norris evaluated the historical development, current conditions, and future potential of the Shortleaf Pine resource and found that this species flourished in the past as a result of repeated disturbance from fire, logging, and clearing for farmland and other developments. However, these types of disturbances and associated reforestation patterns have been virtually eliminated in much of our region, so that little Shortleaf Pine regeneration occurs today. Although some older individual Shortleaf and Virginia pines are still present at the Arboretum, these trees are gradually dying out. Southern pine beetle infestations in recent years have hastened the demise of these pines, and remnants of their trunks are scattered through-out the forest floor. Virginia Pine is described in the February Featured Plants.

Shortleaf pine can be recognized by it’s platy bark, straight needles (3-5 in. long) borne in fascicles (bundles) of 2-3 and a flat-topped crown. The seed cones, which mature in 2 years, are ovoid to conic in shape with stout, sharp prickles on the umbo (a knobbed protuberance on the cone scales). Shortleaf Pine is an important timber tree in the South-east, with its wood used for lumber, plywood, boxes and crates, and pulpwood.

Winter Fruits

Late December - Early January

As one walks the Arboretum trails at this time of year, the fruits of a variety of woody plants and vines can be seen. Our native Dogwood, American Holly and Greenbriar are found along with several non-native, invasive plants, such as Oriental Bittersweet, Chinese privet, and Amur Honeysuckle. Some of these fruits, such as those of the Dogwood provide food for a variety of birds (e.g., robins, cedar waxwings) and small mammals. Six of the more common winter fruits found at the Arboretum are described below.