Knowing what trees are growing in the park, greenway, or other forested area is vital. The types and frequencies of trees can provide a significant amount of information. For instance, an area dominated by one species can indicate the potential for insect and disease problems. (Dutch elm disease taught us that a monoculture of American elms along city streets is an invitation to disaster.) Also, knowing the species mix present can be a guide to developing diversity by planting less common species of trees.

Information on species typically is recorded by species name. Either the common or the scientific name can be used. Some inventory systems use a species code. This is useful to speed data recording, but it requires familiarity with the codes. Unless an individual is doing an extensive inventory, memorizing codes is not practical.

Occasionally inventories will record variety or cultivar, if known. Because cultivars and varieties are so similar to the species, collecting this information typically is not recommended unless there is a specific use for this data. An inventory will sometimes record only genus information, such as oak, elm or hickory, but species specific information is preferred.