The Tree Board has developed a recommended list of trees for public spaces, and in an advisory way, for private spaces. The list includes an array of native species and is presented in relation to typical spaces where trees can be planted along streets and highways (see the matrices on the next few pages). The following points are outlined for a better understanding of planting opportunities.

Interchanges/Grade Separations: The interchange and crossover areas between thoroughfares and freeways can often be more fully landscaped using a variety of species.

Medians: The emphasis on median tree planting using a range of species has and should continue to be a major planting program.

Parking Lots and similar “Hardscape”: Some species have to be avoided, especially fruit-bearing trees and heat-sensitive varieties.

Planting Strips (or Verges): These are the spaces between sidewalks and road pavement. The size of the mature tree in relation to the planting space is a major consideration.

Sidewalk Areas: Certain trees are better on sidewalks than others. Some trees, like sweet gums, should be avoided in that their hard fruit can be like ball bearings under foot.

Utility Lines: The height of utility lines varies, but generally small trees should be used to avoid conflicts where massive pruning would be needed or where limbs could fall onto electrical lines.

Visibility Concern Areas: These are spaces where drivers should be able to see oncoming traffic. Intersections are not the only example; parking lot islands are another. Evergreens and species that cannot be easily trimmed should be avoided.

Yards Adjoining Rights-of-way: The yards next to many streets are the most prominent spaces for tree planting. While not within the “public realm,” yard spaces often define the streetscape of our neighborhoods and can be a major solution in providing consistency in the streetscape of major thoroughfares.

Planting Wells within Sidewalks: There are various situations where wide sidewalks and planting wells will be needed, including downtown, the coliseum area and various shopping districts. Species that are tolerant of harsh conditions are identified.

Large Tree Group: Mature height generally more than 50 feet
Almost all the trees in this group are native species. The use of native plants is important for a number of reasons. Native trees are significant in sustaining the ecosystem. Other plants and organisms are adapted to such trees. Birds, insects and mammals use native trees to fulfill their biological needs. These large trees create canopy and make a major impact in creating an urban forest or park-like setting. Cities with significant street tree programs judiciously use large tree species in creating their streetscapes. Care should be used in planting large trees because they do not always tolerate harsh, urban conditions.

The presence of these large trees is most lacking along major thoroughfares. Large Group Species should be the most often selected in tree planting programs.

Unacceptable trees: some large trees have been purposely left off the list because they have various limitations, including messy fruit, thorny branches, hard nuts that make walking difficult, root systems that tear up sidewalks and drains, or intolerance to urban conditions. These include: buckeyes, chestnuts, hickories, walnuts, silver maples, beeches, honey locusts and black locusts.

There are other large trees that are good for wildlife, including such nut-bearing trees as hickories and walnuts, that could be planted in yards but are not on the recommended list because of the problems they can create when planted near sidewalks or other urban situations. •

Medium Tree Group: Mature height generally 30 to 50 feet
While this group contains many native species, a variety of ornamental species is also included in the matrix. Trees on this list can be used in many situations, including such places as medians, smaller planting strips, and sidewalk planting wells. Some trees in this group, such as sassafras, should be considered understory trees and planted with the large shade trees previously listed.

Small Tree Group: Mature height generally less than 30 feet
This list includes many of the native trees that seasonally brighten Knoxville’s landscape, including flowering dogwood, redbud and sourwood. Also included in the list are a variety of ornamental trees that are known to survive well in the region. The smaller trees should be typically planted along with larger, deciduous trees. This is recommended for two reasons: they serve to complement the taller trees on the landscape and they sometimes need the shade of other trees so they are not roasted in hot, dry conditions. Dogwoods are particularly sensitive to harsh conditions.

There has been a considerable loss of dogwoods in recent years, which the Tree Board sees as a significant problem in that the enjoyment of the dogwood trails could be undermined. The various disease-resistant varieties of dogwoods should be emphasized in future planting programs.