Forest and Shade Trees of Iowa

Flowering Trees

280 n a t u r a l h i s t o r y a n d u s e s o f i o wa’s t r e e s Needle-blight diseases can cause dieback and decline in longneedle pines, especially Austrian pine (shown here) and ponderosa pine. c o n i f e r s 281 Douglas-fir is one of the most important timber trees in the United States, especially the large trees of the Pacific Northwest. Its wood is used for lumber, plywood, mine timbers, poles, fencing, laminated beams, and millwork. Another important use of this valuable tree is for Christmas trees, especially in the West. Baldcypress, Taxodium distichum (L.) Rich. A conifer from the southern swamps might seem ill-suited to planting in Iowa, but the baldcypress grows very well in the warmer parts of the state, and not only in wet sites. There are anecdotal reports of trees in Minnesota, and the species should be tried in northern Iowa. Seed sources from the northwest part of the range in Illinois and Indiana are especially worthy of trial. Baldcypress is among the few conifers that are deciduous. Its soft, ferny leaves are light green in summer, then turn orange-brown in autumn. Cultivated trees are narrowly to broadly pyramidal in habit and grow to 60 feet or more. They may or may not produce the distinctive “knees” of wild trees, peculiar outgrowths of the roots whose function is not understood. Baldcypress is native to swamps in the southern United States but grows well when planted in Iowa. 282 n a t u r a l h i s t o r y a n d u s e s o f i o wa’s t r e e s Yews, Taxus L. Yews are among the most beautiful of conifers, and because of their bushy habit and tolerance of pruning, they are prized for landscaping. Though adapted to varied sites, they are intolerant of soils that are poorly drained or very dry, and winter injury can be a problem where exposed to wind and sun. Shrubby but not dwarf, they can become small trees and overgrow the space where they’re planted. Cultivated yews are Eurasian in origin, but Iowa does have a native species, the Canada yew (T. canadensis Marsh.). A prostrate shrub only 2 to 3 feet high, it grows on rocky bluffs and moist wooded slopes in eastern Iowa. Deer love both native and cultivated species and have killed or severely damaged our native plants in more accessible locations. Arborvitae or Northern White Cedar, Thuja occidentalis L. No one is certain why this handsome tree was named arborvitae, a Latinized form of the French l’arbre de vie or “tree of life.” Some credit the tree’s longevity , which may exceed 400 years. Others cite a sixteenth-century story in which a tea brewed from the tree’s bark and leaves cured scurvy in early explorers. A third possibility is the tree’s evergreen foliage—evergreens have long symbolized eternal life and are frequently planted in cemeteries. Arborvitae is valued for landscaping in Iowa and sometimes planted in farm windbreaks, especially in the northeastern part of the state. With its dense foliage, relatively slow growth, and tolerance of pruning, it is a good choice for hedges and screens. Cultivars of varied sizes and shapes are available, including some that are dwarf and rounded, useful for small gardens and foundation plantings. Arborvitae is an adaptable tree and one of the few conifers that tolerates wet sites. Though hardy and relatively free of diseases, it is susceptible to winter injury when planted in dry locations. Deer favor its foliage and can do severe damage during the winter months. The natural range of the arborvitae includes the Great Lakes states, New England, and southeastern Canada. It has escaped from cultivation in a few sites in northeastern Iowa, where it can be seen on seepy limestone road cuts. c o n i f e r s 283 Where native, it grows in a variety of sites but is most commonly found in swamps, along lakeshores, and in similar moist habitats, often forming thickets . Wild trees grow 40 to 50 feet tall with an oval to oblong crown and are often multiple-stemmed. Foresters know the arborvitae as the northern white cedar. The word “cedar,” like “fir” and “pine,” is used...