In particular in large area forest inventories, it is necessary to define what a tree is; it is hardly necessary for example, for a plantation forest inventory with few planted species or in forest management inventories in temperate regions where there are maybe 10 species.
There are always shrubs that can, in some cases, possibly reach larger dimensions and it must be clear how to deal with them when they occur on a forest inventory plot. It also needs to be decided how to deal with bamboo and palms: include them or not? The stipulated definition of what a tree is, might have direct consequences on the forest definition.
It is a good idea to generate before the inventory field work starts a list of all species that are known to grow in the inventory regions. It is clear that in some cases, in particular in species-rich tropical forest environments, it will be difficult or impossible to make that list complete, but it is needed in any case. In this list, all species are then listed with their scientific names and the (known) local names; each species receives a code; in many countries there is an established coding system for tree species.
According to the FAO definition (FAO 1998), a tree is defined “as a woody perennial plant with a single main stem or in the case of coppice, with several stems, and having more or less definite crown. This definition includes bamboos, palms and other woody plants that meet the above criteria.” Sometimes, a minimum height at maturity, e.g. 5m and 7m, is also given as a part of tree definition.