Birch trees are admired for their graceful, delicate foliage and outstanding bark characteristics. The European white birch (Betula pendula) has been widely planted but it usually is short-lived (15 to 20 years) because of bronze birch borers to which it is particularly susceptible when not in very good health.
The paper or canoe birch, Betula papyrifera, also is popular because of its pure white bark. It is not so susceptible to bronze borer attack and may live to 150 years in native northern stands, but is not resistant to heat or drought.
The river birch (Betula nigra) is recommended by Ohio State University specialists because of its resistance to borer and other insect attacks and its cinnamon-colored exfoliating (flaky) bark.
River birch foliage is a deep green and boasts a medium shade because the leaves are small and the branch texture moderately coarse. Grass can grow very well even under a mature tree. Yellow autumn color can be relatively good in some areas, in others it may go from green to brown without passing through yellow. The tree seldom suffers storm damage because of small branches attached at angles.
Initials carved in the bark when young are obscured with age. This is in contrast to the white-barked birches where initials carved in the trunk remain for 30 to 40 years.
Young river birch trees were planted in the Shade Tree Evaluation Plot at Ohio Agricultural Research and Depvelopment Center as 5-foot whips in 1975. In autumn 1978 the trees averaged 16.9 feet tall and 12 feet in diameter with 3.6 inch trunks. This is more than twice as fast as some of the more rapidly growing Norway and red maples.
River birch has been relatively insect and disease resistent in the OARDC evaluation plot. It appears to have extreme tolerance to the bronze birch borer, according to Dr. T. D. Sydnor, head of the shade tree testing project.
The birch leaf miner is a serious problem on some of the white birches. No such problem exists for the river birch, Sydnor says. No protective spray program is necessary for this tree.
River birch reaches 90 feet in warm, rich bottomlands. It tolerates standing water for short periods of time.
The Japanese white birch (Betula platyphylla) is being tested at the National Arboretum in Washington and in northern Wisconsin by the Forest Service. It grows rapidly and produces attractive white bark at an early age. It will tolerate poor soil conditions and even grows well in sod. It has resistance to the bronze birch borer and is cold hardy throughout most of the U.S.
The goal of the project at the National Arboretum has been to develop superior white-barked birches that have good growth rate and tree form, white bark at an early age, resistance to bronze birch borer and birch leaf miner, and amenable to cultivation in urban areas at the mid-latitudes of the U.S. where European and American species are seldom successful longterm landscape trees, according to Dr. Frank S. Santamour, supervisory research geneticist at the Arboretum.
On the other hand, the main objectives of the Forest Service research have been to test various exotic birches for hardiness in the rigorous climate of Northern Wisconsin, to search for species with faster growth and better form than the native species, and to assemble a pool of germ plasm for use in species hybridization work.
In forestry, where propagation is largely by seed, these tests are carried out routinely and are considered to be of great economic importance. In arborculture, where major emphasis has been on the selection and vegetative propagation of cultivars, such testing has been largely neglected, and some useful studies are long overdue, the reason report said.
In March 1973, seed of various kinds of birch were supplied to the National Arboretum. They were sown in greenhouse flats in March, and the seedlings were planted on a plowed and disced area in Beltsville, Md., where the soil was so poor that nettles and volunteer Virginia pine were the major vegetation before plowing. Some were also planted randomly in sod at Glen Dale, Md.
By the end of the 1976 growing season, when the trees were 4 years old, gray birch surpassed all others in growth performance.
The gray birch is noted for its ability to pioneer on disturbed land and thrive under adverse condition. However, it is fairly short-lived and not a choice landscape tree.
The next best were the five Japanese white birch collections from the main island of Honshu. These tree were variable in growth rate, and the tallest tree in planting (16.3 feet) was a Japanese white birch. Furthermore, the trees showed excellent form characteristics, and, on the larger trees, the darker outer bark had peeled to reveal white bark. All in all, the Japanese species were far superior to all others in this test and in the unreplicated sod planting. The bark whitening of Japanese white birch is early, a distinct landscape (and marketing) asset in comparison to species that only show white bark after many years of growth, according to the research report.