Superior Shade Tree Selections for the Southeastern United States

The maples

Fall color and canopy form of the red maple cultivars in the shade tree project have been reported by Fare et al.(1). The most consistent fall color has been expressed in the cultivars ‘Autumn Flame’, ‘Bowhal’, ‘Gerling’ and ‘Tilford’. Attrition was high in many of the cultivars during the first three years of the test due to bud union incompatibility. The only cultivar that had no trees die from bud union incompatibility was ‘Red Sunset’.

Among the fastest growing red maples in the study have been the cultivars ‘Armstrong’, ‘Scarlet Sentinel’, ‘Karpick’ and ‘Schlesingeri’ (Table 1). Cultivars having broader canopy forms to this point in the evaluation include ‘Autumn Flame’ (4.3 m x 4.1 m), ‘Red Sunset’ (5.0 m x 4.8 m), ‘Schlesingeri’ (5.4 m x 5.6 m) and Acer rubrum species (5.0 m x 5.3 m). ‘Karpick’ and ‘Armstrong’ are more upright in growth habit, having canopy dimensions of 3.2 m x 3.6 m and 3.7 m x 3.6 m, respectively. The upright forms have not been susceptible to breakage in spite of the acute branch angles and closely spaced branching pattern.

The oaks

Sawtooth oak (Quercus acutissima) has been one of the fastest-growing trees in the project at a rate of 112.8 cm per year (Table 1). The canopy form is a broad oval and somewhat open in character. It was described by one visitor to the project as, “…a good climbing tree”, because of the uniform branch spacing on the trunk. The leaves are 10 to 15 cm long with bristle-toothed margins. Fall color is not an ornamental feature. It has shown some inconsistent yellow fall color with the norm being light brown leaves that are retained into late fall and even as late as immediately prior to leafing out in the spring. Some of the more juvenile foliage is typically held until late winter. All of the trees in the study have produced copious amounts of acorns. No significant pest problems have been observed.

Chestnut oak (Quercus prinus) has proven to be a fast-growing native oak, having a mean annual growth rate of 82.3 cm. The canopy form is oval. Branch distribution is uniform and has been structurally sturdy so far in the study. Fall color has been variable from red to yellow, not really a notable ornamental feature. Leaf drop is fairly uniform, routinely shedding by Late November. No significant pest problems have been observed.

Overcup oak (Quercus lyrata) is another one of the faster-growing oaks. It is native to the Southeastern United States and the 100% survival rate of the tree in this study testifies to its being well-adapted in the region. No pests of any significance have been observed in the study. The canopy is broadly rounded and very uniform. Trees have produced large quantities of acorns. Fall color is not a significant ornamental feature of this tree, however, leaf drop has tended to be uniform and condensed into a short time span, usually from mid-through late November.

Shumard oak (Quercus shumardii) is native from southern Michigan to northern Florida and from eastern Texas to North Carolina. Survival rate is 100% and although it has not been in the project since the beginning, this tree has been one of the best-performing red oaks in the study to date. Canopy form is oval and consistent from tree to tree. It has shown a fast rate of growth. Foliage color is dark green in the summer and fall color is consistently red. Leaf spot seems to be a regular feature of Shumard oak in the test, however, it has not seemed to impair tree growth or overall appearance. No other significant pests have been noted.

Other superior trees

‘Heritage’ river birch (Betula nigra ‘Heritage’) was planted winter 1982. All of the trees in the study have a single trunk. Canopy form is an irregular oval to slightly pyramidal shape. Growth rate has been rapid, especially early in the study. Mean height more than doubled from year one to year three (Table 1). Bark characteristics of Betula nigra ‘Heritage’ differ from the native Betula nigra in that the bark of the cultivar exfoliates from the trunk and sizeable branches in larger sheets than the native. Also, the bark color is lighter in appearance in the former than the species.

After an initial attrition rate of 56% Ogeechee tupelo (Nyssa ogeche) has performed well in the evaluation. The tree is native to low wet areas along the lower Costal Plain which may account for the initial loss of trees since the study site is unlike the native habitat. Trees are uniform in size with a broadly rounded canopy, broader than tall with a height of 6.1 m and spread of 6.5 x 6.5 m. The 10- to 15-cm long obovate to elliptical leaves have a medium green summer coloration, consistently turning a deep red to burgundy in the fall. While the flowers are not ornamentally significant, they are highly attractive to pollinating insects. The fruit produced are fairly attractive and abundant four-cm long red to maroon drupes. The fruit are not persistent and under some trees create a carpet of fruit on the ground in the early fall.

Chinese pistache (Pistacia chinensis) has been one of the fastest growing trees in the test with a mean height increase of 88.4 cm per year. The canopy is less broad than tall giving the tree an oval form. Branch structure has been durable with absence of breakage or litter. Summer leaf color has been medium green and fall coloration has shown some variation within the species, ranging from red to reddish-orange, but usually vivid. Leaf drop has been uniform and generally occurs from early through mid-November. No significant disease or insect problems have been observed.

Pondcypress (Taxodium distichum nutans) has a striking pyramidal form. It has been reported as difficult to transplant, however in this study a survival rate of about 78% was realized. Trees have been uniform in growth rate and form. Growth rate has been rapid at 88.4 cm per year which is faster than the other two cypresses in the test, Taxodium mucronatum (70.1 cm per year) and Taxodium distichum (51.8 cm per year). While usually associated with less dry site, tree performance to date suggests a greater tolerance of soil conditions than previously expected. No knees have formed among any of the trees in the study. Fine textured light to medium green summer foliage color, rust to burnt orange fall foliage color, fastigiate form and reddish-gray bark have been aesthetically appealing attributes in this species.

While the trees presented have numerous superior attributes, some characteristics may make them undesirable for some landscape situations. All four of the oak species produce acorns which could be a disadvantage. Fruit produced by Nyssa ogeche could create litter problems as well, particularly in areas with significant pedestrian traffic. In addition, several of the trees develop a large canopy fairly quickly so in sites with restricted overhead space their use may be limited.

These and other trees will continue to be evaluated in this ongoing project.