Status of Street Tree Inventories in the U.S.

The Problem

One of the problems faced by most city foresters is a lack of information about the trees that constitute their urban forest. Where and how many trees are there on city streets? How many specimens of each species are present? How old are they? Are they vigorous or do they need help? How tall are the tallest? What percentage needs pruning or other maintenance? Answers to such questions facilitate planning the maintenance, removal and planting of street trees. As part of a project to design and implement a tree-inventory system for cities, we investigated the status of urban tree-inventory systems in the United States.

Methods

During the summer and fall of 1973 we mailed 510 questionnaires to cities throughout the United States to learn whether they now conduct or plan soon to conduct a periodic or continuous inventory of street trees. Approximately two-thirds of the questionnaires were addressed to individuals on the 1972 mailing lists of the Society of Municipal Arborists and ISTC Yearbook whose titles indicated that they are city or village foresters or arborists, tree wardens, superintendents of a parks and recreation department or a bureau of forestry, or commissioners of forestry. The remaining one-third of the questionnaires were addressed simply to “City Forester” of cities whose population exceeds 50,000 inhabitants. This paper is based on the 172 replies received (we did not mail a follow-up questionnaire to non-respondents). We do not know the total number of cities in this country that have a formal department assigned to tree care but, assuming that the head of such a department is a member of SMA or ISTC, we feel that we have an adequate sample to make valid statements.

The Sample

The 172 replies came from 166 cities in 35 states and 6 cities from three Canadian provinces. We divided the sampling area into five regions (Figure 1); responses received within each region from cities that do or do not inventory were:

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Figure 1.

Number of cities sampled in United States and Canada, by region, state and province.

Unless otherwise noted, we detected no appreciable differences in mean responses between regions or between cities that do or do not inventory. Individual states heavily represented in our sample are California with 22 replies, Illinois with 16 and Michigan with 15.

Of those cities that furnished population information, approximately one-half (84 of 165) contain fewer than 75,000 inhabitants; relatively few large cities now conduct an inventory:

Of those cities that have counted their trees, approximately one-half (68 to 138) contain fewer than 20,000 street trees; cities that do inventory tend to have fewer trees than cities which do not:

Results

Seventy percent of the respondents said that they do not now conduct a periodic or continuous inventory of street trees. The most frequently cited reasons (68%) reflect a lack of funding; approximately one of every six (18%) city foresters and their superiors feel that such a project is not worth the investment:

Two-thirds of these respondents (more than one-half of whom are in Regions 2 and 5) said that their predecessors had never conducted such a survey. Asked whether they plan to begin an inventory by July 1976, one-third do, one-third do not and one-third are uncertain. Asked if they have access to a computer, 39% do, 31% do not and 30% are uncertain.

On the average, cities that do conduct a periodic or continuous inventory have been doing so for nine years:

Fifty-five percent of the cities that do inventory collect data continually throughout the year, 31% gather information periodically throughout the year, and the remainder collect data sporadically. The majority of cities gather information from May through August but many also inventory during fall and winter. Of 53 respondents who conduct inventories, 89% retrieve information by hand and 9% use computers.

All cities were asked how they use their survey data or how they would use it if they were to begin an inventory. Planning maintenance was the most frequently cited use, followed closely by planning tree planting, planning tree removal and evaluating the performance of new trees.

Cities in Region 2 have had considerably less inventory experience than cities in other regions.

We asked all cities how frequently they do inventory or how frequently they would inventory if they were to begin a street-tree census program. Among cities that do inventory, 35% (of 17 replies) do so once every 3-4 years; among those that do not, 40% (of 105 replies) would inventory once every 5-6 years:

We asked cities that do inventory how many workers they use in their survey crews and how many crew members hold college degrees in forestry or related fields. In the 48 cities that furnished this information, the average survey crew consists of 2.2 members, and one of every four members holds a college degree:

Regions 1 and 2 employ a greater percentage of professionals on surveys than do other regions. We asked all cities if they plan to add a professional assistant to their city-forestry staff (not necessarily as part of an inventory program) by July 1976; of the 150 who answered this question, 19% do, 48% do not and 33% are uncertain.

Twenty-seven cities stated how many trees they survey per month per crew member:

We asked all cities either to state the cost of their current survey or to estimate the cost of a survey were they to begin one (81 cities furnished this information but for each region we excluded the maximum and minimum cost reported because a few respondents furnished questionable data). Actual cost per 1,000 street trees ranges from $96 to $311 (averaging $127) among 23 cities that do inventory whereas estimated costs range from $80 to $331 (averaging $156) among 48 cities that do not inventory:

In Regions 2, 4 and 5 wide differences exist between the average cost of surveys in cities that do inventory and the average estimate of what an inventory would cost in cities that do not inventory, but the differences are not consistent.

On the basis of population, the annual cost for 28 cities that do inventory ranges from $18 to $57 (averaging $26) per 1,000 inhabitants whereas the estimated annual cost ranges from $26 to $51 (averaging $35) for 53 cities that do not inventory:

Again, the differences between the actual and estimated costs are not consistent.

We asked for an estimate of the total number of street trees in each city, by species; 93 cities furnished usable information (Table 1). In Region 4, for example, the 13 cities that responded contain a total of 746,000 street trees, 39% of which are Acer and 15% of which are A. Platanoides (Table 1). The genus Acer also constitutes nearly one-quarter of all street trees in Regions 1 and 3. In Region 2, 36% of all street trees are Quercus, one-half of which are Q. virginiana. Ulmus americana represents 52% and 20% of all the street trees in Regions 3 and 4. Region 5 exhibits the most diversity of species used for street trees. Of the 75 genera and 150 species cited, the 10 genera and 10 species listed in Table 1 play an important role in American cities.

Recipients of our questionnaire were asked to list the three most pressing street-tree problems they faced in 1973. To develop a quantitative ranking of the problems, we assigned three points to those cited as most pressing, two points to those ranked second and one point to those ranked third. Diseases, insects and maintenance represented 76% of all the ranking points assigned:

Diseases were assigned 37% of the ranking points by the 156 cities that responded, and they are particularly troublesome in Regions 1 3 and 4 (Table 2). Vascular diseases are the most serious problem, representing 52% of the ranking points from the 38 cities in Region 3 and 28% of the total ranking points from 156 cities. Dutch elm disease was most frequently rated as the most pressing problem, particularly in Region 3 where it represented 39% of all ranking points.

Insects are the second most pressing problem currently faced by city foresters throughout the country. They are especially troublesome in Region 2, where defoliators alone represent 21% of the ranking points (Table 2). Maintenance is an important problem in all regions except Region 1. Construction and replanting appear to be important problems only in Regions 4 and 5.

Asked what single street-tree problem they thought would be most pressing in 1978, 36% of 149 respondents cited maintenance.

Three specific kinds of maintenance problems that are expected to be most pressing in 1978 are pruning-fertilizing-bracing-cabling, removal and replacement of trees and a lack of qualified manpower (Table 3). Diseases are expected to be less of a problem than maintenance in 1978, but Dutch elm disease is expected to remain a serious problem in Region 3. Replanting problems are expected to be more troublesome in 1978 than in 1973 but the reverse is true with respect to insects.

Discussion

Although 30% of the respondents do inventroy street trees, we suspect that some of these inventories are of limited value because of one or more reasons: observations are made when tree crowns are leafless, few data are collected per tree and most data are retrieved by hand rather than by computer. Moreover, only one-third of these respondents stated the frequency between their surveys and only one-half cited how many trees they inventory per month. This suggests that their inventories are not being conducted on a regular or comprehensive basis.

Lack of funding was the fundamental reason cited by two-thirds of the respondents who do not inventory, yet their estimates of what they thought a survey would cost per 1,000 trees exceeded costs of ongoing surveys by an average of 23%.

Many cities that do not inventory are interested in beginning a survey, as evidenced by the fact that one-third of them plan to start one by July 1976. In our judgment these newcomers will be or should be looking for guidance. For example, 61% of the respondents who do not survey stated that they either have no access to a computer or are uncertain as to access. If they are willing to look for guidance, surely they can find computer access and programming help in their own cities or at nearby towns, universities, business establishments or state and federal offices.

Maintenance is expected to be the primary street-tree problem by 1978. We believe that a periodic or continuous comprehensive survey of urban trees will be an invaluable tool to pinpoint maintenance problems and to hlep plan and schedule daily work, particularly in the larger cities, where inventories are not common. Relatively few cities in the United States are now committed to a comprehensive inventory of street trees. In our opinion a familiarity with what computers can do and a realization that computerized surveys are less expensive than expected will convince city foresters that a street-tree inventory is a good investment.