Options in Street Tree Inventories

Many options are available for street tree inventories to meet the unique needs and budgets of most municipalities. Goals and objectives must be clearly defined, type and longevity of inventory decided on, and data collection specifications clearly developed. The purpose and size of the inventory will determine whether to computerize the information. Available options are outlined and discussed. Resum6. Plusieurs options sont disponibles pour un inventaire des arbres de rues afin de satisfaire les besoins et les budgets particuliers de la plupart des municipality. Les buts et les objectifs doivent etre clairement definis, le type et la duree de I'inventaire determines, et les specifications pour la prise de donnees bien developpees. Le but et I'envergure de I'inventaire determiners la pertinence d'informatiser ('information ou non. Les options disponibles sont pr6sent6es et discuses. During the 1970s there was s surge of interest in street tree inventories (9), mainly due to availability of Federal urban forestry funds. Although some of these inventories are still in use, most have been discarded, primarily because of problems accessing, understanding and updating the data. Interest in tree inventories has increased again in the mid-1980s. Most of these inventories are paid for by the cities from their general revenue funds. The common motivations for conducting inventories are the desire to manage trees more efficiently and to reduce potential liability resulting from tree failure. If an urban forest management information system is to be useful now and in the future, the data needed for management decisions must be identified and inventory options reviewed. In this paper, we discuss these options and raise questions which will help cities to obtain an inventory that will be useful in improving their urban forestry program. Why do an Inventory? Before conducting an inventory, the goal or purpose of that inventory must be identified (12). You must clearly define which trees you are interested in and why you want information about them. Not until the 'why' has been clearly defined can you identify the specific information to collect for each tree. There are numerous reasons why a tree inventory should be conducted (11). The first is to determine the need for a tree management program. Are trees growing well with little need for pruning, planting or removal? An inventory can help make this determination. If all trees are growing well and streets are well stocked, then a program may not be needed. Numerous mature trees with dead limbs, standing dead trees and/or areas with no trees, indicate that a program is definitely needed. Secondly, knowledge of tree values or total value of the tree resource can be used to justify the need for, or existence of, a tree management program. Realtors often tout the value of trees since trees often increase the value of residential property. Municipal decision makers can more easily evaluate urban forestry programs, when they know current investment in trees and cost/benefits of proposed programs. Tree values can be determined for each tree or can be projected from a representative sample of trees. An inventory can also identify and prioritize tree work to be done. An inventory can identify trees that need pruning or removal, and sites to be planted. With the total quantity of work determined, plans can be made to accomplish that work. Good inventory data make it possible to project budgets for routine tree maintenance work. Increasing work efficiency is another major benefit of a tree inventory. Inventories that determine maintenance requirements of each tree make it possible to prioritize work. Hazardous trees may be identified so work can be efficiently scheduled and routed. If weather interferes with one type of work (e.g. large tree climbing/pruning) alternative work types (e.g. small tree training) can be located in nearby areas so crews do not have to waste time. This paper is published with the approval of the Director, Utah Agricultural Experiment Station, Utah State University, Logan, UT as a Journal Paper No. 3433 Journal of Arboriculture 14(2): February 1988 37 Inventories can also be useful in public information and education. Information on tree species, value, hazard potential, planting priority, canopy cover and density may all be extracted from an inventory. This information can be used to educate citizens as to the need for, and benefits from, well managed trees. This information can aid in planning for development. Tree species can also be evaluated to prepare planting recommendations for use in-house and for distribution to interested citizens and local nurseries. Inventory Type Defining the objective of the inventory makes it possible to determine the type of inventory, i.e. how much data will be collected and how it will be updated for future use. Specific Problem Inventories collect information about one problem or condition. The information can be used to prepare contracts or schedule work. These inventories collect minimal data, and can be completed quickly and inexpensively. Hazardous tree surveys, Dutch elm disease inspections, stump inventories, and planting site inventories are common examples. Hazardous tree surveys are conducted annually in many cities, and collect the absolute minimum information that all cities should have. Typically, an observer in a vehicle looks for potentially threatening conditions and records the problem and address. Marking hazardous trees during the inventory is no longer recommended since this may increase liability problems. Partial Inventories involve data collection from a sample or small portion of the city. Depending on the percentage of the tree population sampled, partial inventories can be completed rapidly and inexpensively while driving or walking. When using the "windshield" option, the observer records data from the vehicle, thus spends little time with each tree. The address is usually not recorded, as other parameters are of primary interest. Ten percent of the tree population is typically examined in a windshield partial inventory. In "on-ground" partial inventories, more data are collected on each tree, usually including the address. On-ground inventories are most often used to prepare tree work contracts. If representative areas are sampled with either option, results can be statistically extrapolated to the entire population. Inventories that include tree location may be expanded until the inventory is complete. With tree location, partial inventories are useful only for statistical generalizations. Complete Inventories examine the entire tree population and may include all municipally owned trees or all trees in an area. Typically, crews walk to each tree and record the required information. Aerial photographs can be used to determine tree location and condition (5). This type of inventory is extremely labor intensive, and thus, time consuming and expensive. Complete inventories can, however, provide the most accurate and most useful information about the urban forest. Complete inventories are routinely used to project budget needs, to prioritize management activities, and to achieve most other inventory goals. Cover Type Surveys are used extensively to characterize commercial forest lands. Recently, they have been used in urban areas to quantify canopy cover and to monitor changes in urban vegetation (7,8). This type of survey is very useful for examining the entire tree population, not only publicly owned trees. Since data on individual trees are not collected, it is better suited for use in long-term land use planning rather than to plan for work and prepare contracts. Cost is relatively low if existing aerial photographs can be used.