Ornamental Plants

Annual Reports and Research Reviews

Urban Foresters Will Need 20,000 Trees for the Year 2000

Summary

There continues to be a real need for increased diversity in urban tree populations to counter the threat of massive losses of over-planted species, such as occurred when Dutch elm disease struck the American elm. Insect and disease sprays are rarely an option for most urban foresters in today's political climate. Reasons for the limited numbers of species are identified.

A survey of 27 urban foresters in Ohio was conducted to identify potential demand for nursery stock for planting in the year 2000 and beyond. Survey results were shared with the nursery industry by publishing the results in the August 1996 Educational Update in The Buckeye. Results of the survey are being shared with urban foresters so that they might know which plants are being requested and might be available for inclusion on a bid list.

We hope to assist nursery production planning by identifying which of the 127 species and cultivars on the survey form are likely to be requested by urban foresters. Plants likely to be in less demand have been identified as well. Some trees that have been requested are ones that producers might not be growing. The needs identified in the survey might encourage producers to grow some new plants and enable urban foresters to increase biological diversity in the urbanscape.

Introduction

A survey was conducted to identify the needs of Ohio's cities and towns for the year 2000 and to enhance the diversity of species being planted along Ohio's streets and highways. Akron's recent street tree inventory identified 58% of the treelawn trees as Acer while University Heights had 45% Acer. Both cities felt the need to diversify but expressed concern over the difficulty in obtaining less commonly grown trees needed to accomplish the task. We feel that these two comments are representative of the feeling of urban foresters in Ohio's cities and towns.

Common guidelines used to foster biological diversity are:

1. No more than 5% of the trees should be in the same species;

Or:

2. No more than 10% of the trees should be in the same species, no more than 20% in the same genus, and no more than 30% in the same family (the 10-20-30 Rule).

We endorse the 10-20-30 rule as a benchmark against which to measure the diversity of the urban forest. Based on Akron and University Heights inventories, it is easy to conclude that there is a real need to diversify.

The difficulty in obtaining "unusual" species is easy to confirm and exists for a variety of reasons. For the nursery manager, a common statement is: "No one ever asked for that before." This statement is often used to rationalize the fact that nursery producers feel that they cannot produce a tree for which they do not have an established market. We can all agree that just growing a tree is a risk. There has to be a market for the product. Hopefully, this paper will help the nursery industry to identify potential markets for uncommon trees which they may not be growing at the present time.

Materials and Methods

Urban foresters were given a paper describing 31 less commonly grown trees. These were trees that had either been raised through the Ohio Production System, or trees that the authors felt had strong potential for use in urban areas. These 31 trees are listed in Table 1 with their common name in bold type. The survey also included more commonly grown trees.

Urban foresters were asked to provide the following information:

• Name and address.
• The size of plants you would normally purchase and an estimate of the total number of trees you expect to plant in the year 2000.
• An estimate of the number of plants of each type you might wish to purchase in the year 2000 for planting in your community.

Forms were then returned to Dr. T. Davis Sydnor, The Ohio State University, 210 Kottman Hall, 2021 Coffey Road, Columbus, OH 43210-1085 for tabulation.

Results and Discussion

The cities of Akron, Bellefontaine, Bexley, Cincinnati, Cleveland, Cleveland Heights, Columbus, Dayton, Dublin, Elyria, Garfield Heights, Grove City, Lakewood, Maple Heights, Medina, Mount Vernon, Sandusky, Springfield, Toledo, University Heights, Upper Arlington, Westlake, and Worthington as well as the villages of Granville, Leetonia, Mount Gilead, and Terrace Park responded to the survey. A total of 19,700 trees were requested and expected to be planted in the year 2000. Table 1 lists all 127 species and cultivars on the survey form and how many plants were requested of each. Trees with few or no requests were also included. Knowing which species had low demand is as important to a producer as knowing which were in high demand.

There were 31 frequently requested species in 23 different genera. Of the species with 200 or more requests, only the Acer, Fraxinus, and Quercus genera included more than one species (Table 1). Of the eight species of Acer that were heavily requested, four (Freemanii, platanoides, rubrum, and saccharum) have been commonly grown in Ohio while four (buergerianum, campestre, ginnala, and griseum) are less commonly grown. Fraxinus contained two commonly and one less commonly grown species in the commonly requested species list. Quercus contained two species, both of which are grown by Ohio growers.

Other heavily requested species included Amelanchier x grandiflora, Carpinus betulus, Celtis reticulata, Corylus colurna, Eucommia ulmoides, Ginkgo biloba, Gleditsia triacanthos, Halesia caroliniana, Koelreuteria paniculata, Malus x cultivars, Ostrya virginiana, Platanus x acerifolia, Pyrus calleryana, Syringa reticulata, Tilia cordata, Ulmus parviflora, and Zelkova serrata. Only Celtis reticulata is not listed in the Ohio Nursery Stock Survey as published by the Ohio Nursery and Landscape Association. The netted hackberry has a particular appeal for urban foresters since it is alkaline soil tolerant and has a mature height of less than 30 feet, which allows it to be grown under power lines for 30 years without pruning for line clearance. Both characteristics are desirable for urban sites.

An interesting result of the survey was the popularity of various genera (summarized in Table 2). There were 3,363 requests for maples of various types which made Acer the most requested genera. This is consistent with maple's current popularity and not unexpected. Fraxinus was requested 1,488 times. Amelanchier and Tilia were requested 1,144 and 979 times, respectively. Gleditsia, Pyrus, and Ulmus were requested more than 700 times each. Syringa has been increasing in popularity in recent years and was requested almost 600 times.

The second most requested genera was Quercus with 1,769 requests. This is surprising since only two oak species appeared in the most requested species list. Eleven oak species were requested moderately (55-256 requests). Oaks have performed well in urban situations since they have been long-lived and relatively free of serious pests. It is interesting to speculate on the impact of gypsy moth feeding on oak performance in urban areas. Gypsy moth is now established in Ohio. Based on the experience of the eastern United States where the gypsy moth has long been established, oaks will not lose their popularity and will remain serviceable, if properly sited.

Nurseries often find that oaks are less desirable from their perspective, since they may require more time to produce salable plants and lack the marketing advantages of clones. Clones have not been as popular with urban foresters as they are with the general public. Urban foresters are more concerned with service life and maintenance costs than they are with aesthetic characteristics such as fall color and flower color, which are often the basis for clonal selection and marketing.

One thing to remember with oaks is that they are seedling grown. Seed source is important when a plant has a large geographic range. Also, in an urban environment, plants may be grown at the environmental equivalent of the northern or western edge of the species' range. Sawtooth, red, and shumard oaks must be from northern seed sources to ensure that the seedlings are cold hardy. Pin oak must be from local seed sources to ensure tolerance to Ohio's neutral to alkaline soils. Seedlings from parent trees, which appear to have been native near McMinnville, Tennessee, have been prone to iron deficiency while seedlings from native Ohio pin oaks have shown high resistance to this problem. Ohio's best producers can use seed sources as a marketing tool if they maintain records.

Ulmus is another surprisingly popular genus with 777 requests. When asked at a recent meeting to predict the most popular genera during the early part of the next century, Davis Sydnor predicted an increase in elm popularity. Perhaps people believe the prediction, but we hope that urban professionals remember that elms were a monoculture in the 1920s. Their extreme tolerance to the stresses associated with urban sites resulted in overplanting early in this century. Elms are no less urban tolerant today than they were 70 years ago. There are many sites where urban tolerance outweighs sensitivity to Dutch elm disease (DED).

The key in proper plant selection is to maximize assets while minimizing liabilities. A disease-sensitive American elm would probably last for five years longer than green ash in a truly urban site. Thus the health of the urban forest would be improved, even if the trees eventually died from DED. Of course, DED-resistant American elms are now available and should receive preference for planting in the 1990s.

A number of trees were not requested by urban foresters. Boxelder, sugar maple seedlings, European bird cherry, Chinese chestnut, and Russian olive received no requests at all. Fewer than 30 requests were received for 11 species where specifying named cultivars was not an option. These included redbud, pagoda dogwood, flowering dogwood, Washington hawthorn, star magnolia, white mulberry, wild black cherry, black locust, European mountain ash, David elm, and Wilson's elm. The reasons for the lack of popularity of these plants were not specifically stated, but likely results from poor service life, overplanting, lack of familiarity with the species, or extreme site specificity.

The seedling versus clone debate has been an interesting one. While the survey was not designed to look at this issue directly, some information emerged and is worth noting. Freeman maple, red maple, silver maple, sugar maple, white ash, and green ash clones were heavily requested while the seedlings had less than 30 requests. This might be expected since the clones of these plants are among the most heavily promoted, and the aesthetic advantages are obviously of interest to urban foresters. Surprisingly, seedlings were requested more than clones for sweetgum, American linden, and littleleaf linden. Aesthetic differences between seedlings and clones are less pronounced for these plants and may account for the result.

One omission in the survey was osage orange. The survey should have noted thornless male selections rather than the seedlings which appeared. Perhaps clones would have been requested more, as fruit and thorns are real problems for the seedlings in urban areas. Thornless male clones such as 'White Sword' and 'Wichita' will allow us to take advantage of the environmental tolerance and moderate size of osage orange while avoiding its liabilities.

Cities are not the only customers for production nurseries. Urban foresters may be more discriminating and more concerned with serviceability than the general public. Still, nurseries may want to consider the popularity or lack of popularity for these plants with cities when deciding on future production planning for these plants.

Another concern of producers is that they prefer plants that are easy to produce profitably. The Ohio State University is concerned about this as are commercial producers. Current research programs focus on alternative production techniques for less commonly grown trees.

American Electric Power's (AEP) Smart Tree program is funding Dr. Struve's investigation on production techniques and performance of uncommon trees for urban use. AEP is particularly interested in trees that could be used under power lines with reduced pruning and thus reduced line-clearing costs. Still, AEP understands that growers must know how to profitably grow a tree in order for that tree to be produced for sale and planted in the urban landscape. Thus, AEP has funded production research.

Trees with scientific names appearing in bold type in Table 1 have been tried in the Ohio Production System (OPS). Results to date have been variable. Most plants respond with vigorous growth, shaving years from traditional production cycles, while other plants perform no better in the OPS system than under standard field production techniques.

This paper has dealt with a variety of issues that have been shared with us over the years. Neither urban foresters nor nursery producers are aware of some of the unusual species that could be grown. Ohio's urban foresters believe that they must increase species diversity. Less common species are difficult to find and purchase. Nurseries need to reduce production risks by growing trees that are in demand. A special need exists for trees that can be grown beneath power lines for 30 or more years without heavy pruning.

Urban foresters, nursery producers, landscape architects, landscape contractors, and utility companies must all understand the need for increased diversity and remain committed to the task. The real truth is that all of us want an improved quality of life; this is especially important for 80% of Ohio's population, as these people live and work in towns and cities of more than 30,000 people.