SHADE TREES FOR THE NORTH PACIFIC AREA

T. W. CHILDS.

The northern part western Washington and Oregon of the Pacific coast region resembles the southern part in several respects, but three differences greatly influence the kinds of shade trees that can be used in the two areas. In western Washington and Oregon, precipitation is greater and more frequent than farther south, average temperatures are lower, and the summer dry season is much shorter. The Pacific coast itself, a long, narrow strip to the west of the barrier ranges, is divided naturally into the northern and southern (that is, California) subdivisions by the main summit of the Siskiyou Mountains.

The unusually favorable climate in western Washington and Oregon permits the use of a wide range of tree species, both native and introduced.

East of the Cascade Range, environmental conditions are ordinarily much less favorable, and the species listed are not generally suitable for that area.

COMMON HACKBERRY develops here into a round-topped tree with a mature height of 40 to 60 feet. Its growth is moderately rapid and it is moderately long-lived. Its shade is of medium density; leaves appear in late April or early May. It resists drought, cold, and wind ; twig brooming (witches'-broom) is not serious. Although inferior to American elm in some respects, common hackberry should be a good yard and street tree in many localities east of the Cascade Range. Its smaller size and relative resistance to pests make it a desirable substitute for elm along narrow streets and in places where the elm leaf beetle is destructive.

THE AMERICAN YELLOWWOOD is a widespreading tree, 50 to 60 feet high when mature. Growth is moderately rapid and it is moderately long-lived. Its small white flowers in long clusters appear in early June. The leaves turn bright yellow in late fall. It is resistant to cold. It is fairly resistant to drought, and relatively free from insect and fungus pests. American yellow-wood has not been planted extensively, but it deserves to become more popular as a street tree and as a yard tree. It is well adapted to the territory west of the Cascade Range and should also do well in the Columbia River Valley and on the Snake River Plain if it is watered occasionally.

SWEETGUM, a rounded, pyramidal tree, has a mature height of 80 to 120 feet. It is moderately rapid in growth, long-lived, fairly resistant to cold and relatively free from pests, but it is susceptible to injury by drought and by wind. Its star-shaped leaves, about 6 inches across, turn crimson or wine purple in the fall. The bark is deeply furrowed. It casts a moderately dense shade and makes rather heavy demands on soil fertility and moisture, so that water and fertilizer must be generously applied if a good lawn is to be maintained. Sweetgum is an excellent street and yard tree. It has attractive form and brilliant fall color.

THE YELLOW-POPLAR, or tuliptree, is narrowly pyramidal to broadly spreading and grows rapidly to 100 to 160 feet. It is long-lived and fairly resistant to cold, but it is intolerant of drought and city smoke. It is relatively free from-pests. The yellow flowers, about 2 inches in diameter, beautiful but not showy, appear in early June. The leaves are keystone-shaped and turn yellow in the fall. The tree requires moist, fertile soil and has a tendency to rob lawns of moisture and nutrients. This handsome tree unfortunately is not well suited to most city locations and is generally undesirable as a street tree. It is recommended for use on larger suburban and country properties for shade and ornament.

THE NORTHERN RED OAK is broadly round-topped. Its growth is moderately rapid, and it may attain a height of 60 to 90 feet. It is moderately long-lived. The shade is of medium density. It resists cold but not drought and is susceptible to root rot. The leaves turn dark red or orange to brown in early fall. It requires considerable space and fertile soil for good development. This oak has proved to be an excellent street tree in the Eastern States and should be equally satisfactory in the Pacific Northwest. If given enough water, the northern red oak may prove to be a valuable shade tree in many localities east of the Cascade Range.

THE OREGON WHITE OAK grows slowly but is very long-lived. Its mature height is 60 to 80 feet. This tree is broadly round-topped and its shade is rather sparse to moderately dense. Old trees frequently are infected with mistletoe and sometimes with wood rots. It requires moderate moisture and soil fertility for good growth, but does not compete seriously with lawns. It adds neither grace nor brilliant color to the landscape, but those lacks are far outweighed by its restful form and air of tranquil permanence. Notwithstanding its slow growth, this fine native should be more extensively used as a yard tree on lots of medium and large size and as a street tree where space is available for its development.

THE PIN OAK may be pyramidal to rounded and irregular, and 50 to 80 feet high at maturity. Its growth is moderately rapid and it is moderately long-lived. Its shade is of medium density. It is fairly resistant to cold but is not resistant to drought. The leaves appear in late spring, turn deep scarlet in late fall, and often remain on the twigs during most of the winter, particularly on young trees. It prefers rich and moderately moist soil, and is more easily transplanted than either northern red oak or the Oregon white oak. It does well in city environments and can be used to advantage along streets.

THE BIGLEAF MAPLE is broadly and compactly round-topped. Its mature height is 60 to 80 feet. Growth is rapid. It is moderately long-lived. Shade is dense. It is susceptible to a wilt disease and often is attacked by insects, which cause "honey-dew" to drip from the leaves. It makes heavy demands on soil fertility and moisture, so that maintenance of a lawn under it is difficult. A disease of unknown cause that affects the leaves and kills the twigs has been observed recently in parts of California. This handsome native has been widely used, and even more widely misused, west of the Cascade Range. It is not a desirable street tree because its roots heave sidewalks badly and its dense growth necessitates frequent and drastic pruning by line-clearing crews. It has also proved unsatisfactory in most city yards because of its space requirements, litter, and its injurious effect on lawns. These failures have more or less obscured the suitability of bigleaf maple for planting along rural roads and around the country homes.

Norway maple is slightly smaller and grows a little less rapidly than bigleaf maple, but is not otherwise preferable.

THE AMERICAN ELM cannot be recommended unqualifiedly for use in the Pacific Northwest. Elm leaf beetle is often serious, and spraying is necessary to control this pest.

PACIFIC MADRONE, a narrowly oblong to broadly round-topped, broadleaf evergreen, has a mature height of 60 to 80 feet. Its growth is moderately rapid and it is long-lived. It gives sparse to medium shade and is resistant to drought but not to severe cold or wind. The small white flowers appear in showy clusters from March to May; the fruits are orange red in late fall. The leaves are oval, 3 to 5 inches long, glossy dark green above and pale below. The bark is thin and pea green or orange to reddish brown. This unusually colorful native is well suited for use as a yard tree west of the Cascade Range, in the Columbia River Valley of central Washington, and perhaps also in favorable localities elsewhere in this region. It is less satisfactory as a street tree, because it scars easily and its smooth bark is a constant temptation to small boys with jackknives. Its appearance is occasionally impaired for a short time by leaf-spotting fungi, but pests seldom cause any permanent harm.

A FEW ADDITIONAL SPECIES are valuable for special situations.

For windy sites in western Washington and northwestern Oregon, the California sycamore is useful.

Rock elm, European linden, and eastern black walnut can be used in the mountains and valleys of eastern Oregon and Washington where conditions are not too severe.

Green ash is satisfactory for the and plateaus east of the Cascade Range.

CONIFERS RECOMMENDED for western Washington and Oregon include several species of cedar, cypress, and pines.

ATLAS CEDAR is pyramidal and 90 to 100 feet high when mature. Its growth is moderately rapid and it is long-lived. Its shade is sparse to medium. It is fairly resistant to cold and pests. Foliage is bluish green or silvery blue in one popular variety blue Atlas cedar. It requires fairly rich soil and moderate moisture.

Atlas cedar and its close relatives, the Deodar cedar and cedar-of-Lebanon, must be given considerable space for good development and for proper display of their attractive forms. They have been successfully used sometimes for street trees. If given an adequate water supply, they should do well in many localities east of the Cascades.

LAWSON CYPRESS has been widely planted because of its rapid growth, the blue-green color of its foliage, and its slender form. It is hardy throughout the region and is long-lived under favorable conditions. Unfortunately, in the Northwest a root disease has killed many fine specimens.

THE CALIFORNIA INCENSE-CEDAR is broadly pyramidal when young, but later it tends to become narrowly columnar to broadly and irregularly pyramidal. Its mature height is 80 to 100 feet. Growth is moderately rapid and it is long-lived. The deep-green, frondlike foliage casts shade of medium to heavy density. The fibrous bark is deeply ridged and reddish to cinnamon brown. The trunk is broad at the base and tapers rapidly. It is fairly resistant to drought, cold, and pests. The ability of California incense-cedar to thrive in city environments is questionable, but it will undoubtedly prove to be valuable for both shade and ornament in large suburban and country yards. It is native to the eastern slope of the Cascade Range as far north as Mount Hood, and should do well in the Columbia River Valley and on the Snake River Plain.

HIMALAYAN PINE is a broadly pyramidal tree that reaches a height of 120 to 150 feet. It grows rapidly and is moderately long-lived. It is fairly resistant to cold and drought. It is susceptible to a fungus twig canker but highly resistant to white pine blister rust. The rather sparse foliage is grayish green. A handsome tree for large yards, the Himalayan pine is not suitable for street planting.

COMMON DOUGLAS-FIR grows moderately fast to a height of 160 to 180 feet, and is long-lived. Its shade is of medium density. It is fairly resistant to cold and drought but not to wind. In some localities, exposure to city conditions has resulted in the slow decline and eventual death of many trees of this species. Douglas-fir is more tolerant of such unfavorable environments when exposed to them from the seedling stage; however, this species seems generally to be more suitable for country than for city use. Seed of local origin should be used east of the Cascade Range, where climatic extremes are much greater than 'in the coastal region and are likely to result in injury to planting stock of nonlocal origin.

Shore pine is valuable for windy situations in western Washington and northwestern Oregon.

T. W. CHILDS conducts research on problems of forest and shade trees. He is a member of the Bureau of Plant Industry, Soils, and Agricultural Engineering, and is stationed in Portland.